WO2013028720A1

WO2013028720A1 - Low distortion athermalized imaging lens

Info

Publication number: WO2013028720A1
Application number: PCT/US2012/051795
Authority: WO
Inventors: Mark L. Oskotsky; Michael J. RUSSO Jr.
Original assignee: BAE Systems Information and Electronic Systems Integration Inc
Current assignee: BAE Systems Information and Electronic Systems Integration Inc
Priority date: 2011-08-22
Filing date: 2012-08-22
Publication date: 2013-02-28
Anticipated expiration: 2014-02-22
Also published as: US20130050840A1; US8867140B2

Abstract

A compact, lens suitable for airborne photography and mapping has distortion less than 0.6% and is athermal from -15°C to + 40°C. The lens is near-telecentric to less than 1 1 °, apochromatic over the wavelength range 450nm - 650nm, and has a full field of view of 60° (high quality field over 53°), The lens can be secondary color corrected. In embodiments, the focal length is 101mm and the back working distance is more than 10mm. Embodiments have a focal plane diameter of 104mm and are compatible for use with a CMOS 1.8 gigapixel multiple FPA. In embodiments, the lens comprises three groups of optical elements, with an aperture located within the second optical group. In some embodiments the first group includes two elements, the second group includes six or seven elements, and the third group include three elements, in embodiments the lens (without window) is less than 180 mm long.

Description

LOW DISTORTION ATHfiRMA LiZED IMAGING LENS

FIELD OF THE INVENTION

The invention relates to optical lenses, and more particularly to low distortio lenses.

BACKGROUND OF THE INVENTION

Aerial mapping is a fast growing market for both military and civil applications. Aerial mapping acquires airborne image data using remote sensing and produces highly accurate topographic maps of ground regions of interest. Depending on the application, the topographic data, produced by aerial mapping are used for evaluation of the dimensions and content of an observed target.

The ability of aerial mapping to provide comprehensive and detailed topographic information depends largely on the capabilities and features of the imaging lens that Is used, including the distortion of the lens (whereby the image shape does not precisely reproduce the object shape, depending on the viewing angle), correction of monochromatic and polychromatic aberrations (including secondary spectrum), telecen tricky, and thermal stability of the lens (ability to produce images over a required range of temperatures). Compactness and a wide field of view are also highly desirable.

U.S. Pat. No 4,333,714 (Jun. 8, 1982) discloses a reverse telephoto wide angle lens for use in Interchangeable photographic cameras. The '714 lens has a wide field of view, but it is far from being telecentric, it not corrected for distortion, and its secondary spectrum is quiet large. Also this lens is not athermalized and refocus of the image plane is required to compensate for the temperature change. At least for these reasons, fhe '714 lens is not useable for remote aerial high resolution photography and precise mapping.

Another example of a reverse telephoto lens is disclosed in U.S. Pat. No 4,235,520 (Nov. 25, 1980), However, the '520 lens is not corrected for distortion, and has a significant field curvature and secondary spectrum. The '520 lens is also not athermalized.

A telecentric lens is disclosed in U.S. Pat. No 6.563 ,650 (May 13, 2003). The '650 lens is designed to work with special beam splitters directing light onto three different LCDs. Spherical aberration is compensated in the '650 lens by the spherical aberration introduced by the beam-splitter. Distortion and secondary spectrum are not corrected.

Yet another telecentric lens is disclosed in U.S . Pat. No 6,639,653 (Oct. 28, 2003). The '653 lens has a small numerical aperture (NA) and large overall length. However, distortion and secondary spectrum are not corrected.

Still another projection lens is disclosed in U.S. Pat. No 6,038,078 (Mar. 14, 2000). The Ό78 lens is rather complicated, has a large overall length and a small field of view.

Yet another telecentric lens is disclosed in U.S . pat. No 5,905,596 (May 18, 1999). as with the '650 lens, spherical aberration of the '596 lens is corrected by the spherical aberration introduced by a beam-splitter, while distortion and secondary spectrum are not corrected.

Optical distortion is a function of the viewing angle. The distortion of lenses used in aerial mapping should be less than 0.5%. Such lenses should be able to operate at different altitudes, from sea level and u to 30000feet.

The index of refraction of all optical glasses varies as a function of wavelength - this is called dispersion. When the chromatic aberration is not corrected, each wavelength is focused at a. different point along the optical axis. If the optical system is achromatized over a given bandwith, the outer wavelengths of the bandwidth have a common focus. The primary axial color is the difference between the focus positions of the outer wavelengths, and should be corrected to achieve good image quality by selecting glass types and lens optical powers to compensate, for the axial color. When this state of achromatizatlon is achieved, the primary color is corrected. The remaining chromatic aberration is referred to as secondary color. Secondary color is the difference between the focus points for the outer wavelengths of the achromatized bandwidth and the central wavelength. Secondary color is the limiting axial aberration in a lens design, and may be a dominating aberration for high resolution lenses used in aerial photography and mapping.

Monochromatic and chromatic aberrations depend on the heights and angles of rays at the optical element surface and the refraction index of the material. These aberrations also depend on the shape of the optical element, and on its locatio with respect to the aperture stop.

The contribution of the optical element to the total axial color is proportional to the square of axial marginal ray height at the lens, its optical power, and the reciprocal of the Abbe number of the lens material.

The Abbe number V_d is given by d = (nd - l) / (nF - nc) 0)

where i j is the index of refraction of the glass at the wavelength of the helium line d (587,6 am), np is the index of refraction at the blue cadmium line F' (479.99 am), and nc* s the index of refraction at the red cadmium line C

(643.85 ran).

Accordingly, the smaller the value of V_d, the greater the chromatic dispersion of the glass.

For the achromatic (axial colo corrected) doublet, the powers and the dispersions of the elements are chosen to produce zero total dispersion by combining two elements to satisfy the following equation:

where

ί - the optical power of the first element,

VJ - the Abbe number of the first element,

Φ? - the optical power of the second element, and

V? = the Abbe number of the second element.

The secondary spectrum SS doublet for a cemented doublet of optical elements having an optical power is given by:

SSdoublet - [(- 1 /Φ)(Ρ. - Ρ₂)]/( V. - V₂) (3) where

P I - partial dispersion of the first element, and

P2 ~ partial dispersion of the second element.

Partial dispersion describes dispersion for any two wavelengths with respect to the base wavelengths F' and C\ For example, the partial dispersion Par- for wavelengths d and F is defined by:

Pdf - (n_d - n_F)/( (iiF' - nc - (4)

Achromatic correction of a triplet is determined by the equation:

Φ)ίν_χ + ₂ί V 2 + Φ -· V 3 = 0 (5) where

Φ ι - the optical power of the first element,

V f = the Abbe number of the first element,

Φ2— the optical power of the second element,

V-2 = the Abbe number of the second element,

Φ;Ϊ ~ the optical power of the third element, and

V:¾ - the Abbe number of the third element.

The condition for the triplet apochromatic correction is:

Ρ ι (Φ _{/ V j ) + Ρ₂(Φ₂/ V₂) + Ρ₃( .3 V,} - 0, (6) Where

Pj = partial dispersion of the third element.

As ambient temperature conditions change, the shapes and positions of optical elements in a lens will change, and the focal length and position of an image formed by the lens will change as well. This is caused by glass expansion and changes in the glass refractive index with temperature. This dependence on temperature can have a significant impact on lens performance. So as to compensate for these changes, either the focal plane array has to be adjusted along the optical axis, or some elements inside the lens have to be moved. However, this approach is highly undesirable, because additional electronics and software are needed to perform and monitor the necessary adjustments.

On the other hand, a lens does not need thermal adjustment when the change of the focus position within the required temperature range stays inside the depth of focus of the lens. The diffraction depth of focus DOF is defined by:

DOF - λ/ΝΑ² (7) where λ is the wavelength and NA is numerical aperture at the image space

For λ = 550nm and F# 4.5 (NA = 0. 1 11): DOF ~ 0.045mm.

Therefore, in this example, if the lens design meets a requirement that all changes of the focus position over a specified range of temperature changes are inside 0.045mm, no refocusing is required.

The Opto-thermal expansion coefficient β of an optical element is a property of the glass material, and it does not depend on the focal length or shape factor of the individual optics. For a single optical element: = ÷ (dn/dTy(n-l) (8) where

a - the thermal expansion coefficient of the glass

n ~ the refractive index of the glass at the current wavelength

T^™ temperature the change of the single element optical power Φ with temperature T is given by: άΦ/άΎ = ( )(-β). (9)

For an optical system comprising more than one optical element, the total change of the optical power <&_syst<:m with temperature T is:

<I _syStem/dT

( 1 } where

Φ; = optical power of a single element, and

ΐ - single element Opto-thermal expansion coefficient.

Combining equations 2 and 10 allows design of an achromatic and athermalized doublet. Combining equations 2, 3 and 10 allows design of an athermalized doublet with a corrected secondary color (apocbromatic correction).

Combining equations 5 and 10 allows design of an achromatic and athermalized triplet. Combining equations 5, 6 and 10 allows design of an athermalized apocbromatic triplet.

Usually the partial dispersion of glasses has a linear dependence on a refractive index and Abbe number. The slope of a line connecting any two glasses determines the amount of a secondary spectrum in a doublet. The secondary spectrum can be reduced by using special glasses or materials with "abnormal¹' dispersion that varies non-!lnearly with the Abbe number, for example FK type glass (Schott) or SFPL (OHARA) or CaF₂.

What is needed, therefore, is a compact, very low distortion, near-telecentric, athermalized lens that is suitable for airborne photography and mapping. SUMMARY OF THE INVENTION

A compact, very low distortion lens that is suitable for airborne photography and mapping has a full field of view of 60° with a high quality performance field of view of over 53°. The lens is near-ielecentric to less than 1 1 ° lack of telecentricity, apochromatie over a light wavelength range of at least 450nm - 650nm, and is athcrmal over a temperature range from - 15°C to ^■<^'- 40°C, Distortion of the lens i less than 0.6%. In various embodiments the focal length is 101mm and the back working distance is more than iOmm.

Embodiments have a focal plane diameter of 104mm and are compatible for use with a CMOS 1 .8 gigapixel multiple FPA (focal plane array) having a 2 x 2 Bayer filter geometry and a pixel size of 2.2μηι x 2.2μηι, wherein each CMOS image sensor pixel includes a series of dielectric layers above the photo detector, with a micro lens on top of each pixel to focus light onto the active area of the pixel floor, thereby minimizing both the amount of light lost and the amount of light incident on adjacent photodiodes, in various embodiments, secondary color is corrected so as to take full advantage of a high resolution FPA. in various embodiments, the lens comprises three groups of optical elements, and the aperture is located within the second optical group, in some of these embodiments, the lens has a total length of less than 180 mm (not including the optical window). In certain of these embodiments the first group includes exactly two optical elements, the second group includes at least six optical elements, and the third group includes exactly three optical elements. in some of these embodiments, the first group of optical elements corrects the lens for pupil spherical aberration, coma, and astigmatism, the second group of optical elements corrects the lens for first order chromatic aberrations, spherical abberaiions, coma, and astigmatism, while also athermalizing the lens, and the third group of optical elements corrects the lens for field curvature and astigmatism. The present invention is a low distortion lens suitable for airborne photography. The lens includes a first optical group including a plurality of optical elements, a second opti cal group, including a plurality of optical elements, a aperture located within the second optical group, and a third optical group, including a plurality of optical elements. The distortion of the lens is not more than 0.6%. The lens has a full field of view of at least 60°, with a quality performance field of 53°, The lens is telecentric to less than 1 1 °. The lens is apochromatic over a range of at least 450 nra to 650 tvm. And the lens is athermal over a temperature range of at least - 15 °C to +40 °C.

In embodiments, the first optical group includes exactly two optical elements, and the third optical group includes exactl three optical elements. In some of these embodiments the second optical group includes exactly six optical elements. And in other of these embodiments the second optical group includes exactly seven optical elements.

In various embodiments, the lens has a focal plane of at least 04 mm. In some of these embodiments the lens is compatible for use with a CMOS 1 .8 gigapixe! multiple FPA (focal plane array) having a 2 x 2 Bayer filter geometry and a pixel size of 2 ,2μηι x 2.2μιη, wherein each CMOS image sensor pixel includes a series of dielectric layers above the photo detector, with a micro lens on top of each pixel to focus light onto the active area of the pixel floor, thereby minimizing both the amount of light lost and the amount of light incident on adjacent photodiodes. in certain embodiments the lens has a length which does not exceed I SOmra, an optical window not being included in the length. In some embodiments at least one surface of one of the optical elements in each of at least two of the optical groups is aspherical. And in other embodiments the first group of optical elements corrects the lens for pupil spherical aberration, coma, and astigmatism, the second group of optical elements corrects the tens for first order chromatic aberrations, spherical abberations, coma, and astigmatism, while also atherm.aliz.ing the lens, and the third group of optical elements corrects the lens for field curvature and astigmatism. In various embodiments: the first optical group has a positive optical power;

the second optical group has a positive optical power;

the third optical group has a positive optical power;

the first optical group includes two optical elements having, in order, a negative optical power and a positive optical power respectively, the first optical group being arranged to converge light received from an object and to direct the converged light onto the second optical group;

the second optical group includes seven optical elements having, in order, a positive optical power, a negative optical power, a positive optical power, a negative optical power, a positive optical power, a positive optical power, and a negative optical power, the second optical group being arranged to converge light received from the first optical group and to direct the converged light onto the third optical group;

the third optical group includes three optical elements having, in order, a negative optical power, a positive optical power, and a positive optical power, the third optica! group being arranged to focus the light from the second optical group onto an imaging surface; and

the optica] groups and optical elements satisfy the relationships given in paragraph [0092] below.

In some of these embodiments both the first optical element and the second optical element of the first optical group are double concave lenses. In some of these embodiments the second surface of the second optical element of the first optical group is aspherical.

In other of these embodiments the first optical element of the second optical group is a double convex lens, the second optical element of the second optical group is a double concave lens, the third optical element of the second optical group is a double convex lens, the fourth optical element of the second optical group is a double concave lens, the fifth optical element of the second optica! group is a double convex lens, the sixth optical element of the second optical group is a double convex lens, and the seventh optical element of the second optical group is a double concave lens, in some of these embodiments the first surface of the seventh optical element of the second optica! group is aspherical. In some of these embodiments the first and second optical elements of the second optical group are cemented to one another. In other of these embodiments the fourth and fifth optical elements of the second optical group are cemented to one another.

In still other of these embodiments the aperture stop is located between the third and fourth optical elements of the second optical group. in yet other of these embodiments the first optical element of the third optical group is shaped as a negative meniscus lens whose concave surface faces toward the object, the second optical element of the third optical group is a positive meniscus lens whose concave surface faces toward the object, and the third optical element of the third optical group is a double conve lens. In some of these embodiments the first optical element of the third optical group is made from CaF2. In other of these embodiments the first surface of the second optical element of the third optical group is aspherical.

In certain embodiments: the first optical group has a negative optical power;

the second optical group has a positive optical power;

the third optical group has a positive optical power;

the first optical group includes two optical elements having, in order, a negative optical power and a positive optical power respectively, the first optical group being arranged to converge light received from, an object and to direct the converged light onto the second optical group;

the second optical group includes seven optical elements having, in order, a positive optical power, a negative optical power, a positive optical power, a negative optical power, a positive optical power, a positive optical power, and a negative optical power, the second optical group being arranged to converge light received from the first optical group and to direct the converged light onto the third optical group: the third optical group includes three optical elements having, in order, a negative optical power, a positive optical power, and a positive optical power, the third optical group being arranged to focus the light from the second optical group onto an imaging surface; and

the optical groups and optical elements satisfy the relationships given in paragraph [003 04] below. in some of these embodiments both the first optical element and the second optical element of the first optical group are double concave lenses, in some of these embodiments the second surface of the second optical element of the first optical group is aspherical.

In other of these embodiments the first optical element of the second optical group is a double convex lens, the second optical element of the second optical group i a double concave lens, the third optical element of the second optical group is a double convex lens, the fourth optical element of the second optical group is a double concave lens, the fifth optical element of the second optical group is a double convex lens, the sixth optical element of the second optical group is a double convex lens, and the seventh optical element of the second optical group is a double concave lens.

In some of these embodiments the first surface of the seventh optical element of the second optical group is aspherical. In other of these embodiments the first and second optical elements of the second optical group are cemented to one another. And in still other of these embodiments the fourth and fifth optical elements of the second optical group are cemented to one another.

In yet other of these embodiment the aperture stop is located between the third and fourth optical elements of the second optical group.

In certain of these embodiment the first optical element of the third optical group is shaped as a negative meniscus lens whose concave surface faces toward the object, the second optical element of the third optical group is a positive meniscus lens whose concave surface faces toward the object, and the third optical element of the third optical group is a double convex lens. In some of these embodiments the first optical element of the third optical group is made from CaF2. And in other of these embodiments the first surface of the second optical element of the third opti cal group is aspherieaL

In various embodiments: all three optical groups have positive optical powers;

the second optical group includes six optical elements having, in order, a negative optical power, a positive optical power, a negative optical power, a positive optical power, a positive optical power, and a negative optical power, the second optical group being arranged to converge light received from the first optical group and to direct the converged light onto the third optical group;

the third optical group includes three optical elements having, in order, a negative optical power, a positive optical power, and a positive optical power, the third optical group being arranged to focus the light from the second optical group onto an imaging surface; and

the optical groups and optical elements satisfy the relations given in paragraph [001 15] below.

In some of these embodiments the first optical element of the first optical group is a double concave lens, and the seeond optical element of the first optical group is a double convex lens. And in some of these embodiments the second surface of the second optical element of the first optical group is aspherieaL

In certain of these embodiments the first optical element of the second optical group is a double concave lens, the second optical element of the second optical group is a double convex lens, the third optical element of the second optical group is a double concave lens, the fourth optical element of the second optical group is a double convex lens, the fifth optical element of the second optical group is a double convex lens, and the sixth optical element of the second optical group is a double concave lens. In some of these embodiments the first surface of the sixth optical element of the second optical group is aspherical. In other of these embodiments the third and fourth optical elements of the second optical group are cemented to one another.

In some of these embodiments the aperture stop is located between the second and third optical elements of the second optical group.

In other of these embodiments the first optical element of the third optical group is shaped as a negative meniscus lens whose concave surface faces toward the object, the second optical element of the third optical group is a positive meniscus lens whose concave surface faces toward the object, and the third optical element of the third optical group is a double convex Sens. And in some of these embodiments the first surface of the second optical element of the third optical group is aspherical.

The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventi ve subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross sectional side view illustrating a first embodiment of the present invention;

Fig. 2 presents a wave front analysis of the embodiment of Fig. i ;

Fig. 3 is a graph presenting MTF data for the embodiment of Fig, 1 ;

Fig. 4 includes a plurality of graphs presenting RIM RAY curves for the embodiment of Fig. 1 ; Fig, 5A presents a graph of field aberration data for the embodiment of Fig. 1 ;

Fig. 5B presents a graph of distortion data for the embodiment of Fig. 1 ;

Fig. 6 is a graph presenting environmental analysis for the embodiment of Fig. 1 :

Fig. 7 is a listing of properties of optical elements for the embodiment of Fig. 1 ;

Fig. 8 is a cross sectional side view illustrating a second embodiment of the present invention;

Fig. 9 presents a wave front analysis of the embodiment of Fig. 8:

Fig. 10 is a graph presenting MTF data for the embodiment of Fig. 8;

Fig. 1 1 includes a plurality of graphs presenting RIM RAY curves for the embodiment of Fig. 8;

Fig, 12 A presents a graph of field aberration data for the embodiment of Fig. 8;

Fig. 12B presents a graph of distortion data for the embodiment of Fig. 8;

Fig. 13 is a graph presenting environmental analysis for the embodiment of Fig. 8;

Fig. 14 is a listing of properties of optical elements for the embodiment of Fig. 8;

Fig. 15 is a cross sectional side view illustrating a third embodiment of the present invention;

Fig. 1 6 presents a wave front analysis of the embodiment of Fig. 15;

Fig, 17 is a graph presenting MTF data for the embodiment of Fig. 15;

Fig. 1 8A includes a plurality of graphs presenting RIM RAY curves for the embodiment of Fig. 1 5; Fig. 18B includes a plurality of graphs presenting additional RIM RAY curves for the embodiment of Fig. 15;

Fig. 19 A presents a graph of field aberration data for the embodiment of Fig. 15;

Fig. 19B presents a grap of distortion data for the embodiment of Fig. 15;

Fig. 20 is a graph presenting environmental analysis for the embodiment of Fig. 1 5; and

Fig. 21 is a listing of properties of optical elements for the embodiment of Fig. 15.

DETAILED DESCRIPTION

The present invention is a compact, very low distortion lens thai is soitable for airborne photography and mapping has a full field of view of 60° with a high quality performance field of view of over 53°. The lens is near-ielecentric to less than 1 1°, apochromatic over a light wavelength range of at least 450nro - 650nm, and is athermal over a temperature range from -1 5°C to + 40°C. Distortion of the lens is less than 0.5%. In various embodiments the focal length is lOl mm and the back working distance is more than 10mm.

Fig.1 is a cross-sectional illustration of a first embodiment of the lens 10 of the present invention. The lens 10 includes a first optical group 20, a second optical grou 30 and a third optical group 40 in order from the object to the image plane. The aperture stop 1 1 is positioned inside the second optical group 30. An image of a distant object is formed on a focal plane array 60. in embodiments, the focal plane array incorporates CMOS with micro lenses, 2 x 2 Bayer filter geometry, and 1.8 Giga pixels. In other applications the image surface 60 may constitute CCD or a direct viewing screen.

In the embodiment of Fig. I the first optical group 20 has an overall positive optical power and is configured to receive light from a remote object and to direct the converged light onto the second optical group 30. The first optical group 20 includes two optical elements 21 and 22, having negative and positive optical powers respectively. As seen in Fig. 1 , the first optical element 21 of the first optica! group 20 has a negative optical power and is a double concave lens. The second optical element 22 has a positive optical power and Is double convex lens. The second surface 22a of the second element 22 of the first optical group may be aspherical so as to reduce the F number of the lens 1 0. The mutual configuration of the two optical elements 21 , 22 of the first optical group 20 corrects the lens for pupil spherical aberration, spherical aberration, coma and astigmatism without introducing a distortion, while satisfying relationships required among the optical elements to achieve high resolution of the lens 10.

The second optical group 30 has a positive overall optical power and is configured to further converge light from the first optical group 20 and to direct diverged light onto the third optical group 40. The second optical group 20 includes seven optical, elements 31 , 32, 33 , 34, 35, 36 and 37, having a positive optical power, a negative optical power, a positive optical power, a negative optical power, a positive optical power, a positive optical power and a negative optical power respectively. The aperture stop 1 1 is located within the second optical group 30 between optical elements 33 and 34. The position of the aperture stop inside the second optical group allows correction of the telecerttricity and improves the compactness of the lens 10. Optical elements 31 and 32 and optical elements 34 and 35 may be cemented to one another as explained in more detail below.

The first optical element 31. of the second optical group 30 is a double convex lens, the second optical element 32 is a double concave lens, the third optical element 33 is a double convex lens, the fourth optical element 34 is a double concave lens, the fifth optical element 35 is a double convex lens, the sixth optical element 36 is a double convex lens, and the seventh optical element. 37 is a double concave lens.

As mentioned supra, the first optical element 31 and the second optical element 32 of the second optical group 30 may be cemented, to one another for the axial and secondary color correction (apoc romatic correction) in the lens 10. Optical elements 34 and 35 may be cemented to one another for the same reason. In various embodiments the first surface 37a of the seventh optical element 37 is spherical so as to compensate for residual monochromatic aberrations across the field of view.

The mutual configuration and choice of glasses of the elements in the second optical group 30 corrects the lens for first order chromatic aberrations, spherical aberration, coma, and astigmatism, while achieving athermalization of the lens 10 through the desired spectrum of 450mn - 650nm.

The third optical group 40 has a positive overall power and is configured to further converge the light from the second optical group 30 and to focus the light onto the focal plane array 60. The third optical group 30 includes optical elements 41 , 42, and 43 having a negative optical power, a positive optical power, and a positive optical power respectively. The first and second optical elements 41 42 of the third optical group 40 are shaped as negative meniscus lenses whose concave surfaces feces toward the object. The third optical element 43 is a double convex lens. The mutual configuration of the third optical group elements corrects the lens 10 for field curvature and astigmatism. In some embodiments the first surface 42a of the second optical element 42 is aspherical so as to correct residual coma, astigmatism and distortion across the field of view while achieving near telecentricity.

The mutual combination of glasses refractive indices and Abbe numbers of the optical elements in the optical groups 20, 30 and 40 provides achromatic correction of the lens 10. The axial color is corrected. Moreover the combination of partial dispersions of the glasses used for the optical elements provides apochromatic correction, i.e. correction of the secondary color in the lens 10. The mutual combination of changes of refractive index with temperature of the optical elements provides athermalization of the lens 10.

In the embodiment of Figure I , the optical groups 20, 30, 40 and their constituent optical elements satisfy the following relations. 0.09<FV F'₂o<0.14

0.8<F',o/ F'30 <l-2

O.KFV F^?4o <0.15

0.75<n₂*/ n₃i ~ mi/ n₃s = n₂i n₃₂™ n₂j/ n₃4<0.95 1.05 n₃₃<1.3

0.95<¾ι/ιι_ίώ<1.35

G.75<n₃₆/ n₃₇<I.l

0.85<R2i/ i i<l.!5

0.65<_ n42<0,9

1.35<V₂,/V₂₂<1.65

0.9<V₂₁/V₃₃<1.1

0.9<V₇.t/V₃₆<l.l

1.55<V₂,/V₃₇<1.75

0.55<V₂₁/V₄₁<0.7S

2.4<V_2!/V₄₂<2.8

1.5<V_2J/V«<1.9

0.0025<P₄,/V_4!<0.0035

0.095<P₄₂/V₂<G.0135

0.2<dn/dT₂1 / dn/dT₂₂<0.35

0.35<dn/dT_2J/ dn/dT₃₁= dn/dTW dn/dT_3S<0.55

0.9<dn/dT_2i/dn/dT₃₃<l.l

0.9<dn/dT₂i/dn/dT₃₆<l.l 0.3 <dn/dT₂ dn/dT₃₇<0.4

-0.1 5<dn T₂₁/ dn/dT_{4 i}<-0.09

0.9<dn/dT_{2 s}/ dn/dT4_?<l .25

0.18<dn/dT₂,/ dn/dT₄₃<0.25 wherein:

F' io is the focal length of the lens 10;

F '20_J F' 30 and F'40 are focal lengths of the first, the second and the third optical groups 20, 30 and 40;

«2 j aad ri22 are refractive indices for the optical elements 21 and 22 of the first optical group;

Π3 1 , 1-32. 1*33₅ n35, rt36 and 11 7 are refractive indices for the optical elements 31 , 32, 33, 34, 35, 36 and 37 of the second optical group 30;

!Ui, ti42 and ii43 are refractive indices for the optical elements 41 , 42 and 43 of the third optical group 40;

V_{2 !} and ^*22 a e Abbe numbers for the optical elements 21 and 22 of the first optical group 20;

Vj j, V32, V33_, V_34i V35_, V36 and V₃₇ are Abbe numbers for the optical elements 31. 32, 33, 34, 35, 36 and 37 of the second optical group 30;

4i _, V42, and ¥43 are Abbe numbers for the optical elements 41 , 42, and 43 of the third optical group 40;

P41 is the partial dispersion for the optical element 41 of the third optical group 40;

P42 is the partial dispersion for the optical element 42 of the third optical group 40;

dn/dT₂i is the refractive index change with temperature for the first optical element 21 of the first optical group 20;

dn/dT22 is the refractive inde change with temperature for t e second optical element 22of the first optical group 20;

dn/dT₃i is the refractive index change with temperature for the first optical element 31 of the second optical group 30; dn/d^'T^'33 is the refractive index change with temperature for the third optical element 33of the second optical group 30;

da dTj4 is the refractive index change with temperature for the fourth optical element 34 of the second optical group 30;

dn/dT35 is the refractive index change with temperature for the fifth optical element 35 of the second optical group 30;

dn/dT?6 s the refractive index change with temperature for the sixth optical element 36 of the second optical group 30;

dn dT₃? is the refractive index change with temperature for the seventh optica! element 37 of the second optical group 30;

dn/dT<n is the refractive index change with temperature for the first optical element 41 of the third optical group 40;

dn/dT₄2 is the refractive index change with temperature for the second optical element 42 of the third optical group 40; and

dn dT 3 is the refractive index change with temperature for the third optical element 43 of the third optical group 40.

The selection of the optical powers of the optical groups and elements, the selection of the refractive indices, the Abbe numbers, and the partial dispersions of the glasses as well as their dn/dT values, provides a high resolution imaging lens with chromatic and apochromatic correction while the defoeusing caused by changes in temperature is less than the depth of focus of the lens.

Wave fron and MTF data for the embodiment of Fig. 1 are presented in Fig. 2 and Fig.3 respectively. The wave front is well corrected over the whole spectrum.. The polychromatic MTF shows good resolution and contract over the entire field.

RIM RAY curves for the embodiment of Fig. 1 are presented in Fig. 4. They show the spherical aberration, coma and chromatic correction over the wavelength range of 450nm ~ 650nm. Astigmatism data is presented in Fig.5 A, and distortion data is presented in Fig.SB. The field is flat and the distortion is corrected to less than 0.2% over the entire field. The change of the focus with temperature is presented in Fig. 6. The amount of defocus over the temperature range of - 15° to 45° is 0.0025mm, which is almost 20 times less than the depth of focus of 0.045mm. The lack of telecentricity is less than 10.7° across the field. A prescription of the lens 10 is presented in Fig. 7. The optical materials include optical glass and CaF2 materials that are common and widely available commercially.

Fig.8 is a cross-sectional illustration of a second embodiment of the lens 100 of the present invention. This embodiment is essentially identical to the embodiment of Fig. 1 , except for the specific relations that the optical elements satisfy. In particular, the lens 100 includes a first optical group 200, a second optical group 300 and a third optical group 400 in order from, the object to the image plane. The aperture stop 1.10 is positioned inside the second optical group 300, An image of a distant object is formed on a focal plane array 600. In embodiments, the focal plane array incorporates CMOS with micro lenses, 2 x 2 Bayer filter geometry, and 1.8 Giga pixels. In other applications the image surface 600 may constitute CCD or a direct viewing screen.

In the embodiment of Fig. 8 the first optical group 200 has an overall negative optical power and is configured to receive light from a remote object and to direct the diverged light onto the second optical group 300. The first optical group 200 includes two optical elements 210 and 220, having negative and positive optical powers respectively. As seen in Fig. 8, the first optical element 210 of the first optical group 200 has a negative optical power and is a double concave lens. The second optical element 220 has a positive optical power and is double convex lens. The second surface 220a of the second element 220 of the first optical group may be aspherical so as to reduce the F number of the lens 100. The mutual configuration of the two optical elements 210, .220 of the first optical group 200 corrects the lens for pupil spherical aberration, spherical aberration, coma and astigmatism without introducing a distortion, while satisfying relationships required among the optical elements to achieve high resolution of the lens 100. The second optical group 300 has a positive overall optical power and is configured to further converge light from the first optical group 200 and to direct diverged light onto the third optical group 40. The second optical group 200 includes seven optical elements 310, 320, 330, 340, 350, 360, and 370, having a positive optical power, a negative optical power, a positive optical power, a negative optica! power, a positive optical power, a positive optical power and a negative optical power respectively. The aperture stop 1 10 is located within the second optical group 300 between optical elements 330 and 340. The position of the aperture stop inside the second optical group allows correction of the telecentricity and improves the compactness of the lens 10. Optical elements 310 and 320 and optical elements 340 and 350 may be cemented to one another as explained in more detail below.

The first optical element 3 1 0 of the second optical group 300 is a double convex lens, the second optical element 320 is a double concave lens, the third optical element 330 is a double convex lens, the fourth optical element 34 is a double concave !ens, the fifth optical element 350 is a double convex lens, the sixth optical element 360 is a double convex lens, and the seventh optical element 370 is a double concave lens.

As mentioned supra, the first optical element 10 and the second optical element 320 of the second optical group 300 may be cemented to one another for the axial and secondary color correction (apochromatic correction) in the lens 100. Optical elements 340 and 3 SO may be cemented to one another for the same reason, in various embodiments the first surface 370a of the seventh optical element 370 is spherical so as to compensate for residual monochromatic aberrations across the field of view.

The mutual configuration and choice of glasses of the elements in the second optical group 300 corrects the lens for first order chromatic aberrations, spherical aberration, coma, and astigmatism, while achieving athermalization of the lens 100 through the desired spectrum of 450nm - 650nm. The third optical group 400 has a positive overall power and is configured to further converge the light from the second optical group 3(50 and to focus the light onto the focal plane array 600. The third optical group 30 inclisdes optical elements 410, 420, and 430 having a negative optical power, a positive optical power, and a positive optical power respectively. The, first and second optical elements 410 420 of the third optical group 400 are shaped as negative meniscus lenses whose concave surfaces faces toward the object. The third optical element 430 is a double convex lens. The mutual configuration of the third optical group elements corrects the lens 100 for field curvature and astigmatism. In some embodiments the first surface 420a of the second optical element 420 is aspherical so as to correct residua! coma, astigmatism and distortion across the field of view while achieving near te!ecentricity.

The mutual combination of glasses refractive indices and Abbe nimibers of the optical elements in the optical groups 200, 300, and 400 provides achromatic correction of the lens 100. The axial color is corrected. Moreover the combination of partial dispersions of the glasses used for the optical elements provides apochromatic correction, i.e. correction of the secondar color in the lens 100. The mutual combination of changes of refractive index with temperature of the optical elements provides athermalization of the lens 100.

In the embodiment of Fig. 8, the optical groups 200, 300, 400 and their constituent optical elements satisfy the following relations.

-O. KF' ioo/ F'2oo <-0.07

1 .35<F F'₃₀₀ < I .55

0.17<F ' J OO/ F ' 4OO <0.19

0.7(Xn₂,o/ n₂2o<0.90

0.80<^η ₂κ)/ η₃ ιο = n₂ t o n₃₅o ^:::: n_{2 i}o ¾20 ~ ¾ u n₃4o<l

Π Ο/ 33o<i .25

0.9<n₃₁₀/ n₃6o^<l -3

0.65<tt36o/ 37o^<i - 5

0,8<^η _4!0 η₄₃ο<0.95

L55<V₂₅₀/V₂₂₀<L85

1.4<V₂u V₃U~V2K)/ 35Q<1.65

0.85 < V 31 ο V₃₂<r^: V350 34ο 1-35

0.95<V₂₁₀OV₃60<1.1

1.45<V₂io/V₄30<1.75

O.G035<P4io/V₄io<0.0055

0.1<P₄₂o/V2o^< .015

0J5<dn/dT_2]0/ dn/dT₂₂₀«).3

0.4<dn/dT₂u) dn/dT_3i0= dn/dT_2l0/ dn/dT₃o₅<0.6

0.85<dn/dT₂ io/dn/dT₃30<l -05

0.8<dn/dT_2!0/ dn/dT₃₆₀<l .1

0.35<dn/dT dti/dT₃₇o<0.5

0.9<dn/dT_2io/ dn/dT₄i₀<1.2

0.85<dn/dT_{2 f} 0/ dn/dT₄₂₀< 1 - 3

0.15<dn/dT₂j₀/ dn/dT₄₃₀<0.3 where:

F'ioo is the focal length, of the lens 100;

F'SOO_J F^*3O0 and F'400 are focal lengths of the first, the second and the third optical groitps 200, 300 and 400; ϊΐ2 ί ο nd «220 are refractive indices for the optical elements 210 and 220 of the first optical group;

11350, ^¾320, ΪΙ330» ⁿ34o_; 11350, »36o and 0370 are refractive indices for the optical elements 310, 320_f 330, 340, 350. 360 and 370 of the second optical group 300; B io, Π420 and n^are refractive indices for the optical elements 41 0, 420 and 430 of the third optical group 400;

V2₁0 and V 20 are Abbe numbers for the optical elements 41 0 and 420 of the first optical group 200;

V₃io, V320, V330. V340, V350, V₃6o and ¥370 are Abbe numbers for the optical elements 3 10, 320, 330, 340, 35, 360 and 370 of the second optical group 300; P410 is the partial dispersion for the optical element 41 Oof the third optical group 400;

P420 is the partial dispersion for the optical element 420of the third optica! group 400;

dn dT2j is the refractive index change with temperature for the first optical element 21 Oof the first optical group 200;

dn dT220 is the refractive index change with temperature for the second optical element 220 of the first optical group 200;

dn dT;i i o is the refractive index change with temperature for the first optical element 31 Oof the second optical group 300;

d d jo is the refractive index change with temperature for the third optical element 330 of the second optical group 300;

dn dT₃5 is the refractive index change with temperature for the fifth optical element 350 of the second optical group 300;

dn/clT₃6o is the refractive index change with temperature for the sixth optical element 360 of the second optical group 300;

dn/dT37o is the refractive index change with temperature for the seventh optical element 370 of the second optical group 300;

dn/d'Lno is the refractive index change with temperature for the first optical element 410 of the third optical group 400;

dn/dT 2o is the refractive index change with temperature for the second optical element 420 of the third optical group 400; and dn dT43o is the retractive index change with temperature for the third optical element 430 of the third optical group 400,

The selection of the optical powers of the optical groups and elements, the selection of the refractive indices, the Abbe numbers, and the partial dispersions, of the glasses as well as their dn/dT values, provides a high resolution imaging lens with chromatic and apo chromatic correction while the defocusing caused by changes in temperature is less than the depth of focus of the lens.

Wave front and MTF data for the embodiment of Fig, 8 is presented in Fig. 9 and Fig, 10 respectively. The wave front is well corrected over the whole spectrum and is polychromatic. The MTF shows good resolution and contract over the entire field. The RIM RAY curves in Fig, 1 1 show the spherical aberration, coma and chromatic correction over the wavelength range of 450nm ^■" 650nm. Astigmatism data is presented in Fig.12 A, and distortion data is presented in Fig, 12B, The field is flat and distortion is corrected to less than 0.3% over the entire field of view.

The change of the focus with temperature is presented in Fig. 13. The defocus over the temperature range of -1 5° to 45° is 0.028mm, which is 1 .6 times less than depth of focus of 0,045mm. Lack of teiecentrieity is less than 9,2° across the field of view. A prescription of the lens 100 is presented in Fig. 14, The optical materials used include optical glasses that are common and widely available commercially.

Fig.15 is a cross-sectional illustration of a third embodiment of the lens 1000 of the present invention. The lens 1000 includes a first optica! group 700, a second optical group 800 and a third optical group 900 in the stated order from the object to the image plane. Aperture stop 80 is positioned inside the second optical group 800, An image of a distant object, is formed on a focal plane array 90, In some embodiments, the focal plane array incorporates CMOS with micro lenses, 2 x 2 Baye filter geometry, and 1.8 Giga pixels. In other embodiments the image surface 60 incorporates CCD or a direct viewing screen.

The first optical group 700 has an overall positive optical power and is configured to receive light from the remote object and to direct the converged light onto the second optical group 800. The first optical group 700 includes two optical elements 701 and 702, having negative and positive optical powers respectively. As shown in Fig. 1 5, the first optical element 701 of the first optical group 700 has a negative optical power and is a double concave lens. The second optical element 702 of the first optical group 700 has a positive optical power and is a double convex lens. In various embodiments, the second surface 702a of the second optical element 702 is asphencal so as to reduce the F number of the lens 1000. The mutual configuration of the two optical elements 701 , 702 of the first optical group 700 provides correction of pupil spherical aberration, coma, and astigmatism, without introducing a distortion, while satisfying relationships required among the optical elements that provide the required performance of the lens 700.

The second optical group 800 has a positive overall optical power and is configured to further converge light from the first optical group 700 and to direct the converged light onto the third optical group 900. The second optica! group 800 includes six optical elements 801 , 802, 803, 804, 805 and 806 having a negative optical power, a positive optical power, a negative optical power, a positive optical power, a positive optical power, and a negative optical power respectively. The aperture sto 80 is located between the optical elements 802 and 803. Elements 803 and 804 can be cemented to one another as described in more detail below. The first optical element 801 of the second optical group 800 is a single concave lens, the second optical element 802. is a double convex lens, the third optical element 803 is a double concave lens, the fourth and fifth optical elements 804 805 are double convex lenses, and the sixth optical element 806 is a double concave lens. The location of the aperture stop 80 inside the second optical grou provides correction of telocentric! ty and compactness of the lens 1000. Further, as mentioned supra, the third optical element 803 and the fourth optical element 804 of the second optical group 800 can be cemented to one another for axial and secondary color correction (apochromatic correction) of the lens 1 000. in embodiments, the first surface 806a of the sixth optical element 806 is sspherical so as to compensate residual monochromatic aberrations across the f eld of view.

The mutual configuration and choices of glasses for the optical elements in the second optical group 8(30 provides correction of chromatic aberrations, spherical aberration and coma, and astigmatism through the desired wavelength range of 450nm - 650nm, while achieving aihermalization of the lens 1000.

The third optical group 900 has a positive overall power and is configured to further converge the light from the second optical group 800 and to focus the light onto the focal plane array 90. The third optical group includes optical elements 901 , 902 and 903 having a negative optical power, a positive optical power, and a positive optical power respectively. The first optical element 901 of the third optical group 400 is shaped as a negative meniscus lens whose concave surface faces toward the object. The second optical element 902 of the third optical group is shaped as a positive meniscus lens whose concave surface faces toward the object. The third optical element 903 is a double convex lens. The mutual configuration of the third optical group elements provides correction of field curvature, distortion, and astigmatism across the field of view. In embodiments, the first surface 902a of the second optical element 902 is aspherical so as to correct residual, coma, astigmatism and distortion while achieving near-telecentricity in the lens 1000.

The mutual combination of refractive indices and Abbe numbers of the optical elements in the optical groups 700, 800 and 900 provides achromatic and apochromatic correction of the lens 1000. The mutual combination of changes of refractive index with temperature provides aihermalization of the lens 1 000.

In the embodiment of Fig. 15, the optical groups 700, 800, 900 and their constituent optical elements satisfy the following relations. 2.6<F F>7oo ^<3·⁴

2<FWF_8Q0<2.6

2.2<F^*iooo/ <2.7

0.75<n_?o',/ ngoi - 11701/ ^η ₇οί Π804- n?o{ n₈0 <l

^{}.95<π₈οί.^/' n₈02~»80i nso5<l-25

1 , 4 < V 701 / V go i - V701 / V $ 03 ~ 7011 Vg 0 s < 1.8

0 -45<V_S0 j /Vgo^^Vso 1 Vso5^;::: <0.75

O,85<V_S03/V_g04 <1.15

2.4<V_70!/V₉o2<2.8

0.004<P₉oi/V₉o]<0.006

0.95<P₉₀2A^902<0.015

0.2<dn/dT₇os dn/dT₇₀2<0.35

0.25<dn/dT _(H/ dn/dTgoi^ dn/dT₇₀?/ d /d7_m^ dn/dT₇₀j/ dndT₈₀6<0.45

0.85<dn/dT₇oi/dn dT802=dn/dT₇oi/dndT805«1.15

0.4<dn/dT₇₀11 dn/dT₈₀4<0.6

0.8<dn/dT₇₀i/ dndT₉₀i<l -2

1 <dn/dT₇₀1/ dn/dT_M2< 1.25

0.1 <dn/dT₇oi/ dn/dT₉₀₃<0.35 where: F' ioeo is the focal length of the lens 1 000;

F'700, F'goo and F'900 are focal lengths of the first, the second and the third optical groups 700, 800 and 900;

n.701 and «702 are refractive indices for the optical elements 701 and 702 of the first optical group 700;

»8oi . ii802> «-803, «80 , «80 and «806 are refractive indices for the optica! elements 801 , 802, 803 , 804, 80S and 806 of the second optical group 800;

« oi , «902 and «903 are refractive indices for the optical elements 901 , 902 and 903 of the third optical group 900;

V₇(H and V702 are Abbe numbers for the optical elements 701 and 702 of the first optical group 700;

Vgoi, V Q2, Vgo3, go4, j¾os and Vgoe are Abbe numbers for the optical elements 801 , 802 , 803 , 804, 805 and 806 of the second optical group 800;

P 0S is the partial dispersion for the optical element 901 of the third optical gr up 900;

Prjo2 is the partial dispersion for the optical element 902 of the third optical group 900;

dn/dT₇oi is the refractive index change with temperature for the first optical element 701 of the first optical group 700;

dn/d^'I^'702 is the refractive index change with temperature for the second optical element 702 of the first optical group 700;

dn dTgoi is the refractive index change with temperature for the first, optical element 801of the second optical group 800;

dn/dT¾02 is the refractive index change with temperature for the second optical element 802 of the second optical group 800:

dn/dTso3 is the refractive index change with temperature for the third optical element 803 of the second optical group 800;

dn d^'Tso4 s the refractive index change with temperature for the fourth optical element 804 of the second optical group 800;

dn/dTgos is the refractive index change with temperature for the fifth optical element 805 of the second optical group 800; dn dTgo_fjvis the refractive index change with temperature for the sixth optical element 806 of the second optical group 800;

dn/dTVsi is the refractive index change with temperature for the first optical element 901 of the third optical group 900;

dn/dT<>02 is the refractive index change with temperature for the second optical element 902 of the third optical group 900; and

dn dT<?03 i is the refractive index change with temperature for the third optical element 903 of the third optical group 900.

The selection of the optical powers of the optical groups and elements, the selection of the refractive indices, the Abbe numbers, and the partial dispersions, of the glasses as well as their dn/dT values, provides a high resolution imaging lens with chromatic and apochromatic correction while the defocusing caused by changes in temperature is less than the depth of focus of the lens.

Wave front and MTF data for the embodiment of Fig. 15 are presented in Fig. 16 and Fig.1 7 respectively. The wave front is well corrected over the whole spectrum and is polychromatic. The MTF shows good resolution and contract over the entire field of view. The RIM RAY curves presented in Fig. 18A and Figure 1 8B show the spherical aberration, coma, and chromatic corrections over the wavelength range of 450nm ~ 650nm. Astigmatism graphs are presented in Fig.l A, and distortion graphs are presented in Fig, 1 B. The field is flat and the distortion is corrected to less than 0.55% over the entire field of view. Data regarding the change of the focus with temperature is presented in Fig. 20. The amount of defocus over the temperature range of - 15° to 45° is 0,02mm, which is 2.25 times less than depth of focus of 0.045mm. The lack of te!ecentrictty is less than 8.5° across the field of view. A prescription of the lens is presented in Fig. 21. The optical materials used in the embodiment of Fig. 15 include optical glasses that are common and widely available commercially.

The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. Jt is not intended to be exhaustive or to limit the invention to the precise form disclosed. Man modifications and variations are possibie in light of this disclosure. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Claims

What is claimed is;

1. A low distortion lens suitable for airborne photography, comprising:

a first optical group including a pluralit of optical elements;

a second optical group, including a plurality of optical elements;

an aperture located within the second optical group; and

a third optical group, including a plurality of optica! elements,

the distortion of the lens being not more than 0,6%,

the lens having full field of view of at least 60°, with a quality performance field of 53°,

the lens being telocentric to less than 1 1°,

the lens being apochromatic over a range of at least 450 nm to 650 nm, and the lens being athermal over a temperature range of at least - 15 °C to +40

°C.

2. The lens of claim 1 , wherein the first optical group includes exactly two optica! elements, and the third optical group includes exactly three optical elements.

3. The lens of claim 2, wherein the second optical group includes exactly six optical elements.

4. The lens of claim 2, wherein the second optica! group includes exactly seven optical elements.

5. The lens of claim 1 , wherein the lens has a focal plane of at least 104 mm.

6. The lens of claim 6_f wherein the lens is compatible for use with a CMOS 1 .8 gigapixel multiple FPA (focal plane array) having a 2 x 2 Bayer filter geometry and a pixel size of 2„2p.m x 2.2pm, wherein each CMOS image sensor pixel includes a series of dielectric layers above the photo detector, with a micro lens on top of each pixel to focus light onto the active area of the pixel floor, thereby .minimizing both the amount of light lost and the amount of light incident on adjacent photodiodes.

7, The lens of claim 1 , wherein the lens has a length which does not exceed 180mm, an optical window not being included in the length.

8, The lens of claim 1. wherein at least one surface of one of the optical elements in each of at least two of the optical groups is aspherical.

9. The lens of claim 1 , wherein the first group of optical elements corrects the lens for pupil spherical aberration, coma, and astigmatism, the second group of optical elements corrects the lens for first order chromatic aberrations, spherical abberations, coma, and astigmatism, while also athermalizing the lens, and the third group of optical elements corrects the lens for field curvature and

astigmatism.

10. The lens of claim 1 , wherein:

the first optical group has a positive optical power:

the second optical group has a positive optical power;

the third optical group has a positive optical power;

the second optical group includes seven optical elements having, in order, a positive optical power, a negative optical power, a positive optical power, a negative optical power, a positive optical power, a positive optical power, and a negative optical power, the second optical group being arranged to converge light received from the first optical group and to direct the converged light onto the third optical group; the third optical group includes three optical elements having, in order, a negative optical power, a positive optical power, and a positive optical power, the third optical group being arranged to focus the light from the second optical group onto an imaging surface;

the focal lengths of the lens and of the optical groups satisfy the

relationships

0.09<F' io/ F*2o <0.14,

Ο. ,ΚΡ',ο Ρ^ο <0.15,

where

F' _to is the focal length of the lens, and

F' ₂0s P' 30 and F^s o are focal lengths of the first, the second and the third optical groups respectively;

the indexes of refraction of the optical eleraents satisfy the relationships

0.75<n_{2 l}/ n_{3 J} = a_{2 i}/ n₃₅ 0. 5, ,

0.85<n₂i ii4 i<L 15,

0.7<n_{4 !}/ n₄₃<0.95,

where

n₂i , and 1122 are the refractive indices of the first and second optical elements of the first optical group, respectively,

n₃i, n₃3, nj5, n₃₆, and n₃? are the refractive indices of the first, third, fifth, sixth, and seventh optical elements of the second optical group, respectively, and

1141 , Π 2 and n are the refractive indices of the first, second, and third optical eleraents of the third optical group, respectively; the Abbe numbers for the optical elements saiisfy the relationships

L35<V₂₁/V₂2<i.65,

1.45<V2i/V3_!-V_2[/V₃₅<L7,

0.95< _.31/V₃2=V₃5 A^₃ < 1.1 ,

Q.9<V_2i/V₃₃<l.L ^■

0.9<V_2i/V₃₆<l.l,

L55<V_ai/V₃7<1.75,

().55<V_2i/V_4!<0.75,

where

V₂i, and V₂₂ are the Abbe numbers for the first, and second optical elements of the first optical group, respectively,

VJI, V32, V33, V34, V_3S, V_36S and V37 are the Abbe numbers for the first, second, third, four, fifth, sixth, and seventh optical elements of the second optical group, respectively, and

V41, 2, and V43 are the Abbe numbers for the first, second, and third optical elements of the third optical group, respectively;

the partial dispersions of the optica! elements saiisfy the relationships

0.0025<P₄|/V_4l<0.0035, and

0.095<P₄2/V 2<0.0135,

where

Ψ41 is the partial, dispersion for the first optical element of the third optical group, and

P42 is the partial dispersion for the second optical element, of the third optical group; and

the changes of refractive index with temperature satisfy the relationships 0.2<dn/dT₃ ! / dn/dT₂₂<0.35,

0.35<dn/dlV dn/dT₃,= dn/dT₂i dn/dT_3S<0.55,

0.9<dn/dT_2I/dn/dT₃₃<l.l_}

0.9<dn/dT₂ i/ dn/dT₃₆< l .1 ,

0,3<dn dT_{2 !}/ dn/dT₃₇<0.4,

-0.1 5 <dn/dT₂₁/ dn/dT₄₁<-0.09.

0.9<dn/dT₂,/ dn/dT₄₂<1 .25, and.

0, 1 8<dn dT_{2 !}/ dn/dT₄₃<0,25,

where

dn/dTii is the refractive index change with temperature for the first, optical element of the first, optical group,

d dT22 is the refractive index change with temperature for the second optical element of the first optical group,

dn d^'T^'3 ! is the refractive index change with temperature for the first optical element of the second optical group,

is the refractive index change with temperature for the third optical element of the second optical group,

dn dT3 is the refractive index change with temperature for the fourth optical element of the second optical group.

da/dTis is the refractive index change with temperature for the fifth optical element of the second optical group,

dn dT₃6 is the refractive index change with temperature for the sixth optical element of the second optical group,

dn/d^'Tj7 is the refractive index change with temperature for the seventh optical element of the second optical group, dn/dT_{4 5} is the refractive index change with temperature for the first optical element of the third optical group,

dn/dT₄2 is the refractive index change with temperature for the second optical element of the third optical group, and dn dT 3 is the refractive index change with temperature for the third optical element of the third optical group.

1 L The lens of claim 10, wherein the both the first optical element and the second optical element of the first optical group are double concave lenses.

12. The lens of claim 1 1, wherein the second surface of the second optical element of the first optical group is aspherical .

13. The lens of claim. 10, wherein:

the first optical element of the second optical group is a double convex lens;

the second optical element of the second optical group is a double concave lens;

the third optical element of the second optical group is a double convex lens;

the fourth optical element of the second optical group is a double concave lens;

the fifth optical element of the second optical group is a double convex lens;

the sixth optical element of the second optical group is a double convex lens; and

the seventh optical element of the second optical group is a double concave lens.

14. The lens of claim 12, wherein the first surface of the seventh optical element of the second optical group is aspherical.

15. The lens of claim 13, wherein the first and second optical elements of the second optical group are cemented to one another,

16. The lens of claim 13, wherein the fourth and fifth optical elements of the second optical group are cemented to one another,

17. The lens of claim 10, wherein the aperture stop is located between the third and fourth optical elements of the second optical group.

18. The lens of claim .10, wherein:

the first optical element of the third, optical group is shaped as a negative meniscus lens whose concave surface faces toward the object;

BAEP-1614-US 38 the second optical, element of the third optical group is a positive meniscus lens whose concave surface faces toward the object: and

the third optical element of the third optical group is a double convex lens.

19. The lens of claim 18, wherein the first optical element of the third optical group is made from CaF2.

20. The lens of claim 1 8, wherein the first surface of the second optical element of the third optical group is asphericah

21. The lens of claim I , wherein:

the first optical group has a negative optical power:

the second optical group has a positive optical power;

the third optical group has a positive optical power;

the third optical grou includes three optical elements having, in order, a negative optical power, a positive optica! power, and a positive optical power, the third optical, group being arranged to focus the light from the second optical group onto an imaging surface;

the focal lengths of the lens and of the optical groups satisfy the

relationships

-0.1 <F F'2oo <-0.07, L35<F'io / F'300 <1.55, and

0.17<F^,ioo/F^,4oo<0.19,

where

F'soo is the focal length, of the lens, and

F^*200_> F'300 and F'400 are focal lengths of the first, the second and the third optica! groups respectively;

the indexes of refraction of the optical elements satisfy the relationships 0.70<n₂io/ n₂20<0.90,

-^/ »35o^<

0,7<ri4jo n42o^<0-85, and

where

1210, and ti22o are the refractive indices of the first and second optical elements of the first optical group, respectively,

»3io, 11330, -Ϊ350, ii360_> and 1137 are the refractive indices of the first, third, fifth, sixth, and seventh optical elements of the second optical group, respectively, and

j _» and n4₃o are the refractive indices of the first, second, and third optical elements of the third optical group, respectively;

the Abbe numbers for the optical elements satisfy the relationships

0.85<V₃ io/ ₃₂o=V_3So/ V₃4o< 1- .15,

2.2<V_{2 l}o/V₄₂o<2.6, and

where

Yim, and V₂₂o are the Abbe numbers for the first, and second optica! elements of the first optical group, respectively,

3 !0_J V320, V330, 340 , ₃5o, Vjw, and V370 are the Abbe numbers for the first, second, third, fourth, fifth, sixth, and seventh optical elements of the second optical group, respectively, and

V410, V420, and V 30 are the Abbe numbers for the first, second, and third optical elements of the third optical gnrap, respectively;

the partial dispersions of the optical elements satisfy the relationships

0,0035<P₄!o V to<0.0055_f and

0.1 <P 2o/V₄2o<0.015,

where

Ρ Ϊ 0 is the partial dispersion for the first optica! element of the third optical group, and

P420 is the partial dispersion for the second optical element of the third optical group; and

the changes of refractive index with temperature satisfy the relationships 0. 15<dn/dT₂ jo/ dn/dT₂₂₍₎«}.3,

0.4<dn/dT₂ io/ dn/dTj to- dn/dT₂io dn/d.T3₀5<0.6,

0.85<dn/dT23o/dn/dT₃3o<1.05,

0.8<dn/d 210/ cte/dT₃₆₀<l · ,

0.35<dn/dT₂io dn dT₃₇o<0.5,

0.9<dn/dT₂i₀/ dn/dT _lo<l

0.8S<dn/dT₂ j₀/ dn/dT₄₂₀< 1 .3 , and

0.1 5<dn/dT_{2 10}/ dn/dT₄₃o<0.3 ,

where dn dTzjo s the refractive index change with temperature for the first optical element of the first optical group,

dn dT22o is the refractive index change with temperature for the second optical element of the first optical group,

dn dT ui is the refractive index change with temperature for the first optical element of the second optical group,

dn/dT₃3o is the refractive index change with temperature for the third optical element of the second optical group,

dn dTj4o is the refractive index change with temperature for the fourth optical element of the second optical group,

dn dTjso s the refractive index change with temperature for the fifth optical element of the second optical group,

n/dTj_fto is the refractive index change with temperature for the sixth optical element of the second optical group,

dn/dT^o is the refractive index change with temperature for the seventh optical element of the second optical group,

dn dT to s the refractive index change with temperature for the first optica] element of the third optical group,

ri dlVio is the refractive index change with temperature for the second optical element of the third optical group, and dn/dT43o is the refractive index change with temperature for the third optical element of the third optical group,

22. The lens of claim 21 , wherein both the first optical element and the second optical element of the first optical group are double concave lenses.

23. The lens of claim 22, wherein the second surface of the second optical element of the first optical group is aspherieai.

24. The lens of claim 21 , wherein: the first optical element of the second optical group is a double convex lens;

the third optical element of the second optical group is a double convex lens;

the fifth optical element of the second optical group is a double convex lens;

the sixth optica! element of the second optical group is a double convex lens; and

25. The lens of claim 24, wherein the first surface of the seventh optical element of the second optical grou is aspherical.

26. The lens of claim 24, wherein the first and second optical elements of the second optical group are cemented to one another.

27. The lens of claim 24, wherein the fourth and fift optical elements of the second optical group are cemented to one another.

28. The lens of claim 21 , wherein the aperture stop is located between the third and fourth optical elements of the second optical group.

29. The lens of claim 21 , wherein:

the first optical element of the third optical group is shaped as a negative meniscus lens whose concave surface faces toward t e object;

the second optical element of the third optical group is a positive meniscus lens whose concave surface faces toward the object; and the third optical element of the third optical group is a double convex lens.

30. The lens of claim 29, wherein the first optical element of the third optical group is made from CaF2.

31. The lens of claim 29, wherein the first surface of the second optica! element of the third optical group is aspherical.

32. The Lens of claim 1. wherein:

all three optical groups have positive optical powers;

the second optica! group includes six optical, elements having, in order, a negative optical power, a positive optical power, a negative optical power, positive optical power, a positive optical power, and a negative optical power, the second optical group being arranged to converge light received from the first optical group and to direct the converged light onto the third optical group;

the third optical group includes three optical elements having, in order, a negative optical power, a positive optical power, and a positive optical power, the third optical group being arranged to focus the light from the second optical group onto an imaging surface;

the focal lengths of the lens and of the optical groups satisfy the

relationships

2<F^, _{ooo F'_g0o <2.6

2.2<FW F'₉oo <2.7

where

F' IOOO is the focal length of the lens, and F^*7oo_» F'goo and FVoo are focal lengths of the first, the second and the third opticai groups respectively;

the indexes of refraction of the optical elements satisfy the relationships

0.75<n7oi/ 11801 ^::" n₇oi/ n₈os- «?οι nso-r^:: n?oj ¾06<1

0. 0<rt_{7Q i}/ Π90 ϊ<ί · ί 5

0.7<n₉oi/ n₉02<O.9

0.75< <soi ni)03<0. 5

where

n?oi_» and n₇₀2 are the refractive indices of the first and second optical elements of the first opticai group, respectively,

ngoi , ngoa. nso.3 » neo , sos, and ngoe are the refractive indices of the first, second, third, fourth, fifth, and sixth optical elements of the second optical group, respectively, and

«901» n<jo2_> and n₉03 are the refractive indices of the first, second, and third opticai elements of the third opticai group, respectively;

the Abbe numbers for the optica! elements satisfy the relationships

l .35<V₇oi/V₇02<1.7

1.4<V₇₀1 /Vgo i= V?o : V8o3~V₇oi V₈o6< 1.8

0.85<V_?oi/V_{90 !}<l . l 5

1.55<V_70i/V_9M<1 .85

where

V₇oi, and V702 are the Abbe numbers for the first, and second optical elements of the first optical group, respectively, gos, so2, ₈o3, _S0 , Vgos, an _S06 are the Abbe numbers for the first, second, third,, fourth, fifth, and sixth opiical elements of the second optical group, respectively, and

oo_h 902, and V_W3 are the Abbe numbers for the first, second, and third optical elements of the third optical group, respectively;

the partial dispersions of the optical elements satisfy the relationships 0.004<P₉₀,/V9oi < .006

where

P90 1 is the partial dispersion for the first optical element of the third optical group, and

P$02 is the partial dispersion for the second optical element of the third optical group; and

the changes of refractive index with temperaiure satisfy the relationships 0.2<dr_!/dT₇₀ i dn/dT₇₍>2<0.35

0.25<dn/dT7o i/ dn/dTgoi- dn/dT₇oi/ dn/dTgo3~ dti/dT₇oj/

0.4 <dn/d T70 _Ϊ / n/dT _{g 0} <0.6

G.8<dn/dlW dn dT90 i<i .2

l <dn/dT₇₀i/ dn dT902<l -25

0. l<dn dT₇₀i/ dn/dT_W3<0.35

where

dn/dT₇oi is the refractive index change with temperature for the first opiical element of the first optical group,

dn/dT₇02 is the refractive index change wit temperature for the second optical element of the first optical group,

dn/dT$<H is the refractive index change with temperature for the first optical element of the second optical group, dn/dT802 is the refractive index change with temperature for the third optical element of the second optical group,

dn/dTs 3 is the refractive index change with temperature for the fourth optica! element of the second optical group,

dn/dTso is the refractive index change with temperature for the fi fth optical element of the second optical group,

dn/dTgos is the refractive index change with temperature for the sixth optical element of the second optical group,

dn/dTgos s the refractive index change with temperature for the seventh optical element of the second optical group,

dn/dTgos is the refractive index change with temperature for the first optical eiement of the third optical group.

dn/dT<jo2 s the refractive index change with temperature for ihe second optical element of the third optical group, and d /dT903 is the refractive index change with temperature for the third optical element of the third optical group.

33. The lens of claim 32, wherein the first optical element of the first optical group Is a double concave lens, and the second optical element of the first optical group is a double convex lens.

34. The lens of claim 33, wherein the second surface of the second optical element of the firs optical group is aspherical.

35. The lens of claim 32, wherein:

the first optical element of the second optical group is a double concave lens;

the second optical element of the second optical group is a double convex lens

the third optical element of the second optical group is a double concave lens; the fourt optical element of the second optical group is a double convex lens;

the fifth optical element of the second optical group is a double convex lens; and

the sixth optical element of the second optical group is a double concave lens.

36. The lens of claim 35, wherein the first surface of the sixth optical element of the second optical group is -a spherical.

37. The lens of claim 35, wherein the third and fourth optical elements of the second optical group are cemented to one another.

38. The lens of claim 32, wherein the aperture stop is located between the second and third optical elements of the second optical group.

39. The lens of claim 32, wherein:

the first optical element of the third optical group is shaped as a negative meniscus lens whose concave surface faces toward the object:

the second optical element of the third optical group is a positive meniscus lens whose concave surface faces toward the object; and

the third optical element of the third optica! group is a double convex lens.

40. The lens of claim 39, wherein the first surface of the second optical element of the third optical group is aspherical,