JPS6381414A - Large aperture lens - Google Patents

Abstract

PURPOSE:To satisfy telecentric characteristic by satisfying a specific condition in a simple constitution of five lenses, namely, negative positive, negative, positive, and positive lenses of five groups and setting the back focus to >=1.2f long value. CONSTITUTION:This lens system consists of five lenses, namely, a first negative meniscus lens n1 having the convex on the object side, a second double convex lens n2, a third double concave lens n3, a fourth positive meniscus lens n4 having the convex on the image side, and a fifth double convex lens n4 having the convex on the image side, and a fifth double convex lens n5 of five groups in order from the object side, and a stop is arranged between the second and third lenses, and condition 0.4f<d4<1f is satisfied where (f) is the focal length of the whole of the lens system and d4 is the distance between the second and fourth lenses. Thus, the back focus is long and the telecentric characteristic is good.

Description

[Detailed Description of the Invention] [Field of Application in CL Industry] 2) This invention relates to a large-diameter lens used in cameras, etc., and is particularly applicable to small video cameras or still video cameras.
This is a large-diameter lens consisting of 5 elements in 5 groups, consisting of negative, positive, negative, positive, and positive lenses, suitable for such applications.

(Advanced technology) In recent years, with the spread of small video cameras and the development of still video cameras, there has been a demand for lenses with large apertures and good telecentric characteristics as lenses for these video cameras and still video cameras.

Furthermore, in video cameras and still video cameras,
Since a low-pass filter such as a quartz plate is disposed between the rearmost surface of the lens and the focal plane to cut out particularly high frequency components, a lens having a long back surface "B" is required.

For a lens with such a large aperture and large back 7 orcus, consisting of 5 elements in 5 groups consisting of negative, positive, negative, positive, and positive,
Lens described in Japanese Utility Model Application Publication No. 60/54111, Japanese Patent Application Publication No. 60/1988
0-269194! Lenses and the like described in the publication are known.

However, the lens described in Japanese Utility Model Application Publication No. 60/54111 has a relatively large aperture with an F number of F 1.8, but it is possible to obtain a large aperture lens with an even larger diameter Fl of about 4 to F 1.6. Furthermore, the telecentric characteristics required for video cameras and still video cameras, especially color video cameras and still video cameras, are not satisfactory. Although it has a large diameter, the back 7 Orcus f
8 is short at about 1f (and the telesend link characteristics are not satisfactory.

Other than that, 5 elements in 5 groups (negative, positive, negative, positive, positive) are 413 Jat lenses with a relatively large back 7 orcus f-day.
JP-A-55-147607, JP-A-57-163
2 No. 2, JP-A-58-179808, etc., interchangeable lenses for 35z/z light plate and %77
Kushimiri's lenses are known, but all of them have F numbers between F2.0 and F3.5, and none of them have satisfactory telecentricity characteristics.

(Purpose of the Invention) This invention has a half angle of view of 23゜, despite having a simple t3 configuration with 5 elements in 5 groups consisting of negative, positive, negative, positive, and positive.
Try to obtain a lens with good performance, with an angle of ~25 degrees, a large aperture with an F number of about 1.4 to 1.6, a good back 7 orcus of 1.2 f or more, and satisfying telecentric characteristics. That is.

(Structure of the Invention) This invention comprises, in order from the object side, the first lens of a negative meniscus lens with a convex surface facing the object side, the second lens of a biconvex lens, the third lens of a biconcave lens, and the third lens of a negative meniscus lens with a convex surface facing the image side. A lens with a five-element configuration in five groups consisting of a meniscus 1jS4 lens and a biconvex Pt5S lens, the second
A pattern is placed in the darkness between the lens and the third lens, and 0.4f<d,<if (1) However, f:
This is a large-diameter lens characterized by satisfying the following conditions: focus of the entire system, α distance d4: distance between the second lens and the Pt53 lens.

In this invention, a so-called retro 7 orcus type lens configuration is adopted, in which a lens having a negative focal length that is advantageous for disabling the back 7 orcus rB is arranged in the first group, and a conventional retro 7 orcus type lens configuration is adopted. The air gap between the second lens and the third lens is larger than that of the lens of
Placing a crest there satisfies the telecentric characteristics. Furthermore, by using a positive meniscus lens with a convex surface facing the image side as the fourth lens, it becomes easier to lengthen the back focus and also make it easier to satisfy telecentric characteristics.

Normally, in a camera such as a video camera or a still video camera that records an image using an imaging means (such as a CCD), the distance between the exit pupil position of the entire lens system and the focal plane of the imaging means is 4 of the diagonal length of the focal plane
It is said that a telecentric characteristic that is sufficient for practical use is obtained if the ratio is 5 times or more, and the lens of the present invention has a sufficient telecentric characteristic, as is clear from the examples described below.

Condition (1) described above is a condition for having sufficient telecentricity and maintaining good aberrations.If d becomes larger than the upper limit, the meridional field curvature increases, and the meridional image field at an intermediate angle of view becomes The difference between the meridional image planes at the maximum angle of view becomes too large, and with a lens as large as the one in the present invention, it becomes impossible to balance the meridional image planes from the intermediate to the maximum angle of view. Furthermore, if the upper limit is exceeded, the distance between the aperture and the lens surfaces located before and after the aperture also increases, leading to an increase in the diameter of the front lens and the rear lens, as well as an increase in coma flare.

Conversely, when d is smaller than the lower limit, the second lens and the third lens
It is not possible to place a fringe between the lenses, and it is not possible to satisfy telecentric characteristics.

Furthermore, it is desirable that the present invention satisfy the following conditions.

50<V, (2) 30>Vz (:() 30>V) (4) 50<(V, +V,)/2 (5)1.
65< (n4+ is)/2 (6) However,
ni: refractive index of the 1st lens vi: Atsube number of the 1st lens As in this invention, in a lens with a long pack focus and a front lens, the two lenses in the front group produce negative chromatic aberration, and the two lenses in the rear group produce negative chromatic aberration. By configuring the three lenses to produce positive chromatic aberration, the chromatic aberration of the entire system is corrected.

The conditions (2), (3), (4), and (5) mentioned above are the conditions for keeping this chromatic aberration good.
) and (5), it will be difficult to satisfactorily correct chromatic aberration while keeping the back 7 orcus fB at 1.2 f or more.

The above-mentioned condition (6) is a condition for maintaining good spherical aberration and curvature of field. If this condition is not satisfied, the curvature of the concave surface of the fourth lens becomes loose (and the convex surface of the fourth lens %tA5 lens becomes loose). becomes strong, so negative spherical aberration and field curvature become large, and furthermore, it becomes difficult to maintain the back 7 for a long time.

(Example) Examples are shown below.

Figure ff11 shows a sectional view of an embodiment of the lens of the present invention.

In a type of camera that forms an image on an imaging means, such as a video camera or a still video camera, a crystal plate is placed between the final surface of the lens and the focal plane of the imaging means.
Because infrared cut plates, protective plates, etc. are involved, aberration correction during lens design usually requires a fairly thick cover plus inserted between the final surface of the lens and the focusing surface! ! (i.e.
This is done in the same state as described above with the crystal plate, infrared cut plate, protection plate, etc. Therefore, in all of the embodiments shown below, aberration correction is accomplished with the cover having a lath.

In the example, 2Y is the diagonal #a of the focusing plane of the imaging means, r is the radius of the lens of the own vehicle, d is the distance between lens surfaces, and n
, V is the refractive index of the lens, Atsube Example 1°f=10 FNol, 65 2m=47″″41
' 2Y = 0.844f:d, ':'''' Back focus f 4 with cover glass converted to air
i, 1.29H.

The distance from the focus plane to the exit pupil is -8,45, with the fringe placed at 0.421f in front of the fifth plane (object 1111).
1f, (- means when the exit pupil is closer to the object side than the focal plane) The spherical aberration, astigmatism, and distortion of Example 1 are compared to Example 2.
゜f=10 FNol, 45 2w=4883' 2
Y = 0.844f Back 7 with cover glass converted to air
Orcus re is 1. Z66f.

The distance from the focal plane to the exit pupil is -8,586f with the fringe placed 0.48f in front of the fifth surface.

The spherical aberration, astigmatism, and distortion aberration of Example 2 are expressed as °°゛''
“° 2nd episode; Example 3゜r=10 FNol, 65 2w=48°00′2Y
=0.844f, -7\product y margin) 35. ,' The pack 7 orcus f day when the cover glass is converted to air is
1.328f.

The distance from the focal plane to the exit pupil is -5,1:17f, with the fringe placed 0.35f in front of the fifth surface.

FIG. 4 shows the spherical aberration, astigmatism, and distortion of Example 3.

(Effects of the Invention) As is clear from the embodiments described above, according to the present invention, it is possible to obtain a large-diameter lens that has good back-to-back focal length, good telecentricity, and good aberration correction.

[Brief explanation of the drawing]

The mi diagram is a cross section of a lens according to an embodiment of the present invention, and fB
2, 3, and 4 are aberration curves of Example 1, Example 2, and Example 3 of the present invention, respectively. Applicant Roku Konishi Photo Industry Company-0,200,2 Ball Itl Cane Tip 1IIL Breath

Claims (1)

[Claims] In order from the object side, the first lens is a negative meniscus lens with a convex surface facing the object side, the second lens is a biconvex lens, the third lens is a biconcave lens, and the third lens is a positive meniscus lens with a convex surface facing the image side. 5 groups 5 consisting of a 4th lens and a 5th lens which is a biconvex lens
0.4f<d_4<1f where f: focal length of the entire system d_4: second lens and third lens. A large aperture lens that satisfies the condition of distance between three lenses.