CA1162767A - Field curvature control - Google Patents
Field curvature controlInfo
- Publication number
- CA1162767A CA1162767A CA000388929A CA388929A CA1162767A CA 1162767 A CA1162767 A CA 1162767A CA 000388929 A CA000388929 A CA 000388929A CA 388929 A CA388929 A CA 388929A CA 1162767 A CA1162767 A CA 1162767A
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- Prior art keywords
- lens
- mirror
- field curvature
- mangin
- radius
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT
An optical element for providing control of field curvature. The element consists of a lens having a first and second surface. The second surface is coated with reflective material. The radiation received by the lens is refracted at the first surface, reflected back from the second surface, and then refracted once again by the first surface. The first and second surfaces have a shape for providing control of field curvature.
An optical element for providing control of field curvature. The element consists of a lens having a first and second surface. The second surface is coated with reflective material. The radiation received by the lens is refracted at the first surface, reflected back from the second surface, and then refracted once again by the first surface. The first and second surfaces have a shape for providing control of field curvature.
Description
- l 1827~7 FIELD CURVATURE CONTROL
CROSS REFERENCE TO RELATED APPLICATIONS
Reference should be made to our copending Canadian patent applications Serial No. 388,788 entitled "Compact Optical System" and Serial No. 388,788 en-titled 'IOptical System Having A Dual Field of View", which are filed on even date herewith and which are assigned to the same assignee as the present appli-cation.
BACKGROUND OF THE INVENTION
The present invention relates to control of field curvature in optical systems. The invention has application in optical systems generally and is par-ticularly advantageous in compact cassegrainian arrangements.
It is particularly important in gimbal-mounted infrared sensor systems typical of, for example, missile born sensors that the system be extremely com-pact. In addition, it is important in such infrared systems to avoid field flatteners or separate lenses placed near the image for controlling field curva-ture; the infrared detector sees itself in any such lens and causes a cold spot in the system output because the detector area is cold. In addition, it is im-portant that the system have a weight distribution providing a relatively small moment of inertia to minimize power requirements for rotating the system by the gimbals.
These requirements have been found to be particularly well satisfied by a concave primary mirror and a convex secondary ~k ~ 1~27~
mirror comprising a config~ration often referred to as a cassegrainian arrangement. (The precise definition of a Cassegrain system is one where the primary mirror is specifical]y a parabola and the secondary mirror a hyperbola. However r ~ystems comprising a concave primary mirror and a convex secondary mirror are no~ often referred to as cassegrainlar, systems without particular reference to the particular geometry of the mirrors.) Two-mirror arrangements of this kind offer the maximum ratio of focal length to system length.
~ he compactness of Euch a configuration is improved ~s the primary mirror focal length is shortened requiring, as a consequence, a related decrease in the focal length of the secondary mirror. As this design feature is extended, such a system normally shows an increasing amount of field curvature arising from the disparity in the magnitude of radii of the primary and secondary mirrors.
In prior art systems, control ~of field curvature has typically been handled through use of field flatteners or additional lenses located within the system. See, for example, U.S. Patent No. 3,515,461, Casas èt al, June 2, 1970, column 2, lines 44-46. ~s previously mentioned, if such a field flattener or corrector is located near the image in an infrared system, it has a distinct disadvantage since the detector can see itself as a reflection in the correcting lens. In addition, systems having such additional lenses are heavier and more complex.
``\ :
~ 1627~7 In systems where these factors are a problem, 8 particular feature of the present invention is the us~ of a mangin mirror having its surfaces shaped for providing control of field curvature without the use of special additional lenses~
Mangin mirrors have classically been used w-th spherical mirrors to correct spherical aberrations. See, for example, the indicated disclosures within the following U.S
Patents:
CROSS REFERENCE TO RELATED APPLICATIONS
Reference should be made to our copending Canadian patent applications Serial No. 388,788 entitled "Compact Optical System" and Serial No. 388,788 en-titled 'IOptical System Having A Dual Field of View", which are filed on even date herewith and which are assigned to the same assignee as the present appli-cation.
BACKGROUND OF THE INVENTION
The present invention relates to control of field curvature in optical systems. The invention has application in optical systems generally and is par-ticularly advantageous in compact cassegrainian arrangements.
It is particularly important in gimbal-mounted infrared sensor systems typical of, for example, missile born sensors that the system be extremely com-pact. In addition, it is important in such infrared systems to avoid field flatteners or separate lenses placed near the image for controlling field curva-ture; the infrared detector sees itself in any such lens and causes a cold spot in the system output because the detector area is cold. In addition, it is im-portant that the system have a weight distribution providing a relatively small moment of inertia to minimize power requirements for rotating the system by the gimbals.
These requirements have been found to be particularly well satisfied by a concave primary mirror and a convex secondary ~k ~ 1~27~
mirror comprising a config~ration often referred to as a cassegrainian arrangement. (The precise definition of a Cassegrain system is one where the primary mirror is specifical]y a parabola and the secondary mirror a hyperbola. However r ~ystems comprising a concave primary mirror and a convex secondary mirror are no~ often referred to as cassegrainlar, systems without particular reference to the particular geometry of the mirrors.) Two-mirror arrangements of this kind offer the maximum ratio of focal length to system length.
~ he compactness of Euch a configuration is improved ~s the primary mirror focal length is shortened requiring, as a consequence, a related decrease in the focal length of the secondary mirror. As this design feature is extended, such a system normally shows an increasing amount of field curvature arising from the disparity in the magnitude of radii of the primary and secondary mirrors.
In prior art systems, control ~of field curvature has typically been handled through use of field flatteners or additional lenses located within the system. See, for example, U.S. Patent No. 3,515,461, Casas èt al, June 2, 1970, column 2, lines 44-46. ~s previously mentioned, if such a field flattener or corrector is located near the image in an infrared system, it has a distinct disadvantage since the detector can see itself as a reflection in the correcting lens. In addition, systems having such additional lenses are heavier and more complex.
``\ :
~ 1627~7 In systems where these factors are a problem, 8 particular feature of the present invention is the us~ of a mangin mirror having its surfaces shaped for providing control of field curvature without the use of special additional lenses~
Mangin mirrors have classically been used w-th spherical mirrors to correct spherical aberrations. See, for example, the indicated disclosures within the following U.S
Patents:
2,730,013, Mandler, Jan. 10, 1956, Col. 1, lines 19 and 46.
2,817,270, Mandler, Dec. 24, 1957, Col. 1, lines Sl - 56 and 60 - 61.
2,817,270, Mandler, Dec. 24, 1957, Col. 1, lines Sl - 56 and 60 - 61.
3,064,526, Lindsay, Nov. 20, 1962, Col. 5, lines 20 - 23 and 66 - 67.
3,296,443, Argyle, Jan. 3, 1967, Col. 2, lines 33 - 36.
3,632,190, Shimizu, Jan. 4, 1972, Col. 2, lines 34 - 39.
See also Rogers, "A Comparison Between Optimized Spheric and ~spheric Optical Systems for the Thermal Infrared", SPIE Vol. 147, Computer-~ided OPtical Design, 1978, pp. 141-14 (text at bottom of page 145).
tIn addition, see U.S. Patent No. 3,527,526, Silvertooth, Sept. 8, 1970, Col. 4, lines 64-67 which discloses use of a mangin in a cassegrainian arrangement for unspecified reasons).
While some of the above patents indicate use of a mangin mirror for correcting other aberrations, it is believed unique to configure mangin mirror surfaces for providing control .
~ 1627~7 of field curvature. As previously indicated, the field curvature problem be-comes more severe as the optical system is made more compact. However, inasmuch as a mangin mirror may also be defined as a lens having its back surface coated with reflective material, it can be uniquely applied to correct the amount of field curvature by controlling the particular shape or radii of mangin mirror surfaces. Thus, for any given objective system or subsystem, the particular field curvature correction may be established by a unique set of values for the two radii of the mangin mirror surfaces. Further, this can be accomplished as an integral part of one of the two mirrors in a two mirror system and, therefore, does not require supplementing such systems with additional corrector lenses.
SUMMARY_OF THE INVF_TION
The present invention is an optical element for providing control of field curvature. The element consists of a lens having a first and a second surface. The second surface is coated with reflective material. The radiation received by the lens is refracted at the first surface, reflected back from the second surface, and then refracted once again by the first surface. The first and second surfaces have a shape for providing control of field curvature.
In accordance with the present invention there is provided an optical element for providing control of field curvature, the optical element consist-ing of a mangin mirror comprising a lens having a first and a second surface,the second surface being coated with reflective material, the radiation received by the lens being refracted at the first surface, reflected back from the second surface, and then refracted once again by the first surface, the first and second surfaces having a shape for providing control of field curvature.
In accordance with another aspect of the invention~ there is provided an optical element for providing control of field curvature, the optical element consisting of a mangin mirror comprising a lens having a first and a second sur-~ ~2~67 face, the second surface being coated with reflective material, the radiationreceived by the lens being refracted at the first surface, reflected back from the second surface, and then refracted once again by the first surface, the first and second surfaces each having a radius defined by the equation l/R = 2/n[(n+l)/rl * 1/r2] where R is the radius of the field curvature, n is the index of refraction of the lens, rl is the radius of the first surface, and r2 is the radius of the second surface.
In accordance with a further aspect of the invention, there is pro-vided an optical arrangement for providing control of field curvature, the arrangement comprising a lens having a first and a second surface, the second surface being coated with reflective ma*erial, the radiation received by the lens being refracted at the first surface, reflected back from the second sur-face, and then refracted once again by the first surface, the first and second surfaces having a shape for providing control of field curvature.
In accordance with yet another aspect of the invention, there is pro-vided an optical arrangement for providing control of field curvature, the arrangement comprising a lens having a first and a second surface, the second surface being coated with reflective material, the radiation received by the lens being refracted at the first surface, reflected back from the second sur-face, and then refracted once again by the first surface, the first and secondsurfaces each having radii which determine the field curvature by the equation l/R = 2[~n-1)/rl-~ 1/r2]/n where R is the radius of the field curvature, n is the index of refraction of the lens, rl is the radius of the first surface, and r2 is the radius of the second surface.
BRIEF DESCRIPTI~N OF TH_ DRAWING
The single Figure illustrates the present invention embodied in a compact optical system.
- 4a -~ :~6~7~
DESCRIPTION OF THE PREFERRED EMBODIMENT
_ There are described in ~his application various ~eatures and functions of a disclosed system which are not the subject of the present invention, but rather are the subject of an invention claimed in the previously mentioned copenâing application entitled "Compact Optical System." The descriptions of these features and functions are included in the present application in order to demonstrate utility of the present invention within an optical system.
Reference is made to the accompanying Figure in which the present invention is illustrated as mirror or lens 12 within a compact optical system. Collimated radiation from a point in the scene is tr`ansmitted through a concentric dome window 10 with appropriate refractions at each surface. The beam is slightly divergent as it impinges upon a concave primary front s~rface mirror 11. It is then converged to mangin secondary mirror 12 at which the radiation is refracted at a first surface of incidence 13, reflected from a back surface 14, and then refracted once again by the first surface.
As previously indicated, a particular feature of the present invention is providing surfaces 13 and 14 with a shape for controlling field curvature. Mangin secondary mirror 12 also reduces convergence of the beam while reflecting it backward, the radiation being focused at a field stop 17. The radiation may then be transmi~ted through collimator 15 comprising lenses 16 and 20 having appropriate refractions at each surface. Lenses 16 ~ ~62767 and 20 collimate the radiation and direct it through exit pupil 21.
In the optical system disclosed, mangin secondary mirror 12 only par-tially corrects field curvature, the field curvature being completely corrected following collimator 15 (lenses 16 and 20). However, in alternate embodiments, surfaces 13 and 14 of mirror 12 may be shaped to completely correct field curva-ture at field stop 17. Thus, mangin secondary mirror 12 may be employed to con-tribute whatever degree of field curvature is necessary to flatten the field or to control the field curvature to the desired flatness.
The field curvature contribution of mangin secondary mirror 12 is l/R
and may be defined by an equation l/R = 2[(n-1)/rl + 1/r2]/n. In this equation, R is the radius of the field curvature, n is the index of refraction of the man-gin mirror lens, rl is the radius of the first surface (surface 13 in the dis-closed embodiment), and r2 is the radius of the second or back surface (surface 14 in the disclosed embodiment). Thus, once the material for the mangin mirror lens is selected, n is known from available references, and the radii of sur-faces 13 and 14 can be calculated to provide any desired degree of field curva-ture control.
The first and second surfaces of mangin mirror 12 also allow one to select any combination of focusing power and field curvature contribution. For the normal situation in which the mangin mirror is thin, power of the mangin mirror is l/f and may be defined by the equation l/f = 2[n/r2 - (n-l)/rl]. In this equation, f is the focal length of the mangin mirror, n is the index of re-fraction of the mangin mirror lens, rl is the radius of the first surface (sur-face 13 in the disclosed embodiment), and r2 is the radius of the second or rear surface (surface 14 in the disclosed embodiment).
Tables 1 and 2 set forth below give the dimensions and parameters of one preferred embodiment of an optical system comprising the present invention.
- 1 ~627~i7 SPECIFICATION-SYSTEM EXAMPLE
Element Radius Thickness Material Conic Constant (inches) (inches) Dome 10 6.0 .30 Zinc Sulfide 5.7 4.8 Primary Mirror 11 -7.166 -2.555 Aluminum -.75102 Secondary Mirror 12 -6.758 -.10 Germanium -5.475* .10 -4.7 Field Stop 17 2.555 .501 Collimator Lens 16 -.818 .401 Germanium -1.047 .01 Collimator Lens 20 1.544 .20 Germanium -.3565 2.340 Exit Pupil 21 1.04 * Surface is Aspheric:
~ ~ 1627B7 Sag r ~ dy4 ~ ey6 ~ fy _ 1 + V 1 - ~K + 1) wnere d = 2.213 x 10-3 y = ~perture height e = -1.459 x 10-3 r = Radius of the surace f = 4.591 x 10-4 k = Conic constant EXA~PLE SYSTE~ PhR~METERS
Telescope Magnification 11.9 External Field of View 2.38 x 3.22 Entrance Pupil Diameter 4.4 in.
Objective F-Number 2.0 Objective Focal Length 8.85 in.
Collimator Focal Length .744 in.
Table 1 is laid out in a manner common in the art; if more than one dimension is given for an element, the dimensions appear in the order that light travels from the scene through the system. For example, for dome 10, the first radius listed of 6.0 inches corresponds to the first surface of dome 10, and the radius of 5.7 inches corresponds to the second surface of dome 10.
In the thickness column of Table 1, the numbers include on-axis air space thicknesses listed in the order in which light travels through the system. Accordingly, the firs~ number of .30 r incn is the thickness of dome 10. ~ The second number of 4.~
inches corresponds to the~ on-axis distance be~ween the second surface of dome 10 and a point that would intersect the radius of the reflective front surface of primary mirror 11. The minus sign associated with the first dimension of 2.555 inches indicates light traveling in a backward direction. The .10 inch number listed in association with mangin secondary mirror 12 indicates the thickness of the mirror, the first number being negative since light is traveling in the reverse direction in its first transit to the reflective back surface 14 of that mirror.
The positive 2.555 inch dimension is the air space distance between first surface 13 of mirror 12 and field stop 17, which is the first focal p~ane. The dimension of .501 inch is the distance between field stop 17 and the first surface of lens 16 within collimator 15. The .401 inch dimension listed in association with collimator lens 16 is the thickness of that lens, the .01 inch dimension being the air space thickness between the second surface of lens 16 and the first surface of lens 20. The .20 inch dimension listed in association with lens 20 is the thickness of that lens, the 1.04 inch dimension being the distance between the second surface of lens 20 and exit pupil 21.
It should be noted/ of course, that the dimensions and parameters listed in Tables 1 and 2 do not represent the present invention, but rather the dimensions and parameters of a system comprising the present invention.
1 ~2~6~
It should also be noted that, while the mangin mirror has been shown as a secondary mirror in the disclosed embodiment, the secondary mirror could be a front surface mirror, and the primary mirror could be a mangin mirror with first and second surfaces shaped for providing control of field curvature.
Alternately, both mirrors could be mangin mirrors with one or both having surfaces so shaped.
Further, although mirror 12 comprising the present invention is disclosed as aspheric see Table 1), a mangin mirror comprising the present invention may also be spherical.
In addition, while a mangin mirror in accordance with the present invention is shown implemented in a cassegrainian arrangement, such an implementation is illustrative only since a mangin mirror in accordance with the present invention may be applied in any optical system wherein radiation may be suitably received, refracted, and reflected by the mirror in order to control field curvature.
Finally, it should be noted that the present invention provides field curvature control. Such control may be desiyned to include only partial correction of field curvature, either without further correction provided by additional system optics or, as in the disclosed example, with further correction by additional system optics (collimator 15 in the disclosed system).
Alternately, the field curvature control provided by the present invention may be designed to completely correct field curvature introduced by other optics within a system.
J 1627~7 The present invention is to be limited only in accordance with the scope of the appended claims, since persons skilled in the art may devise o~her embodiments still within the limits of ~he claims.
.
3,296,443, Argyle, Jan. 3, 1967, Col. 2, lines 33 - 36.
3,632,190, Shimizu, Jan. 4, 1972, Col. 2, lines 34 - 39.
See also Rogers, "A Comparison Between Optimized Spheric and ~spheric Optical Systems for the Thermal Infrared", SPIE Vol. 147, Computer-~ided OPtical Design, 1978, pp. 141-14 (text at bottom of page 145).
tIn addition, see U.S. Patent No. 3,527,526, Silvertooth, Sept. 8, 1970, Col. 4, lines 64-67 which discloses use of a mangin in a cassegrainian arrangement for unspecified reasons).
While some of the above patents indicate use of a mangin mirror for correcting other aberrations, it is believed unique to configure mangin mirror surfaces for providing control .
~ 1627~7 of field curvature. As previously indicated, the field curvature problem be-comes more severe as the optical system is made more compact. However, inasmuch as a mangin mirror may also be defined as a lens having its back surface coated with reflective material, it can be uniquely applied to correct the amount of field curvature by controlling the particular shape or radii of mangin mirror surfaces. Thus, for any given objective system or subsystem, the particular field curvature correction may be established by a unique set of values for the two radii of the mangin mirror surfaces. Further, this can be accomplished as an integral part of one of the two mirrors in a two mirror system and, therefore, does not require supplementing such systems with additional corrector lenses.
SUMMARY_OF THE INVF_TION
The present invention is an optical element for providing control of field curvature. The element consists of a lens having a first and a second surface. The second surface is coated with reflective material. The radiation received by the lens is refracted at the first surface, reflected back from the second surface, and then refracted once again by the first surface. The first and second surfaces have a shape for providing control of field curvature.
In accordance with the present invention there is provided an optical element for providing control of field curvature, the optical element consist-ing of a mangin mirror comprising a lens having a first and a second surface,the second surface being coated with reflective material, the radiation received by the lens being refracted at the first surface, reflected back from the second surface, and then refracted once again by the first surface, the first and second surfaces having a shape for providing control of field curvature.
In accordance with another aspect of the invention~ there is provided an optical element for providing control of field curvature, the optical element consisting of a mangin mirror comprising a lens having a first and a second sur-~ ~2~67 face, the second surface being coated with reflective material, the radiationreceived by the lens being refracted at the first surface, reflected back from the second surface, and then refracted once again by the first surface, the first and second surfaces each having a radius defined by the equation l/R = 2/n[(n+l)/rl * 1/r2] where R is the radius of the field curvature, n is the index of refraction of the lens, rl is the radius of the first surface, and r2 is the radius of the second surface.
In accordance with a further aspect of the invention, there is pro-vided an optical arrangement for providing control of field curvature, the arrangement comprising a lens having a first and a second surface, the second surface being coated with reflective ma*erial, the radiation received by the lens being refracted at the first surface, reflected back from the second sur-face, and then refracted once again by the first surface, the first and second surfaces having a shape for providing control of field curvature.
In accordance with yet another aspect of the invention, there is pro-vided an optical arrangement for providing control of field curvature, the arrangement comprising a lens having a first and a second surface, the second surface being coated with reflective material, the radiation received by the lens being refracted at the first surface, reflected back from the second sur-face, and then refracted once again by the first surface, the first and secondsurfaces each having radii which determine the field curvature by the equation l/R = 2[~n-1)/rl-~ 1/r2]/n where R is the radius of the field curvature, n is the index of refraction of the lens, rl is the radius of the first surface, and r2 is the radius of the second surface.
BRIEF DESCRIPTI~N OF TH_ DRAWING
The single Figure illustrates the present invention embodied in a compact optical system.
- 4a -~ :~6~7~
DESCRIPTION OF THE PREFERRED EMBODIMENT
_ There are described in ~his application various ~eatures and functions of a disclosed system which are not the subject of the present invention, but rather are the subject of an invention claimed in the previously mentioned copenâing application entitled "Compact Optical System." The descriptions of these features and functions are included in the present application in order to demonstrate utility of the present invention within an optical system.
Reference is made to the accompanying Figure in which the present invention is illustrated as mirror or lens 12 within a compact optical system. Collimated radiation from a point in the scene is tr`ansmitted through a concentric dome window 10 with appropriate refractions at each surface. The beam is slightly divergent as it impinges upon a concave primary front s~rface mirror 11. It is then converged to mangin secondary mirror 12 at which the radiation is refracted at a first surface of incidence 13, reflected from a back surface 14, and then refracted once again by the first surface.
As previously indicated, a particular feature of the present invention is providing surfaces 13 and 14 with a shape for controlling field curvature. Mangin secondary mirror 12 also reduces convergence of the beam while reflecting it backward, the radiation being focused at a field stop 17. The radiation may then be transmi~ted through collimator 15 comprising lenses 16 and 20 having appropriate refractions at each surface. Lenses 16 ~ ~62767 and 20 collimate the radiation and direct it through exit pupil 21.
In the optical system disclosed, mangin secondary mirror 12 only par-tially corrects field curvature, the field curvature being completely corrected following collimator 15 (lenses 16 and 20). However, in alternate embodiments, surfaces 13 and 14 of mirror 12 may be shaped to completely correct field curva-ture at field stop 17. Thus, mangin secondary mirror 12 may be employed to con-tribute whatever degree of field curvature is necessary to flatten the field or to control the field curvature to the desired flatness.
The field curvature contribution of mangin secondary mirror 12 is l/R
and may be defined by an equation l/R = 2[(n-1)/rl + 1/r2]/n. In this equation, R is the radius of the field curvature, n is the index of refraction of the man-gin mirror lens, rl is the radius of the first surface (surface 13 in the dis-closed embodiment), and r2 is the radius of the second or back surface (surface 14 in the disclosed embodiment). Thus, once the material for the mangin mirror lens is selected, n is known from available references, and the radii of sur-faces 13 and 14 can be calculated to provide any desired degree of field curva-ture control.
The first and second surfaces of mangin mirror 12 also allow one to select any combination of focusing power and field curvature contribution. For the normal situation in which the mangin mirror is thin, power of the mangin mirror is l/f and may be defined by the equation l/f = 2[n/r2 - (n-l)/rl]. In this equation, f is the focal length of the mangin mirror, n is the index of re-fraction of the mangin mirror lens, rl is the radius of the first surface (sur-face 13 in the disclosed embodiment), and r2 is the radius of the second or rear surface (surface 14 in the disclosed embodiment).
Tables 1 and 2 set forth below give the dimensions and parameters of one preferred embodiment of an optical system comprising the present invention.
- 1 ~627~i7 SPECIFICATION-SYSTEM EXAMPLE
Element Radius Thickness Material Conic Constant (inches) (inches) Dome 10 6.0 .30 Zinc Sulfide 5.7 4.8 Primary Mirror 11 -7.166 -2.555 Aluminum -.75102 Secondary Mirror 12 -6.758 -.10 Germanium -5.475* .10 -4.7 Field Stop 17 2.555 .501 Collimator Lens 16 -.818 .401 Germanium -1.047 .01 Collimator Lens 20 1.544 .20 Germanium -.3565 2.340 Exit Pupil 21 1.04 * Surface is Aspheric:
~ ~ 1627B7 Sag r ~ dy4 ~ ey6 ~ fy _ 1 + V 1 - ~K + 1) wnere d = 2.213 x 10-3 y = ~perture height e = -1.459 x 10-3 r = Radius of the surace f = 4.591 x 10-4 k = Conic constant EXA~PLE SYSTE~ PhR~METERS
Telescope Magnification 11.9 External Field of View 2.38 x 3.22 Entrance Pupil Diameter 4.4 in.
Objective F-Number 2.0 Objective Focal Length 8.85 in.
Collimator Focal Length .744 in.
Table 1 is laid out in a manner common in the art; if more than one dimension is given for an element, the dimensions appear in the order that light travels from the scene through the system. For example, for dome 10, the first radius listed of 6.0 inches corresponds to the first surface of dome 10, and the radius of 5.7 inches corresponds to the second surface of dome 10.
In the thickness column of Table 1, the numbers include on-axis air space thicknesses listed in the order in which light travels through the system. Accordingly, the firs~ number of .30 r incn is the thickness of dome 10. ~ The second number of 4.~
inches corresponds to the~ on-axis distance be~ween the second surface of dome 10 and a point that would intersect the radius of the reflective front surface of primary mirror 11. The minus sign associated with the first dimension of 2.555 inches indicates light traveling in a backward direction. The .10 inch number listed in association with mangin secondary mirror 12 indicates the thickness of the mirror, the first number being negative since light is traveling in the reverse direction in its first transit to the reflective back surface 14 of that mirror.
The positive 2.555 inch dimension is the air space distance between first surface 13 of mirror 12 and field stop 17, which is the first focal p~ane. The dimension of .501 inch is the distance between field stop 17 and the first surface of lens 16 within collimator 15. The .401 inch dimension listed in association with collimator lens 16 is the thickness of that lens, the .01 inch dimension being the air space thickness between the second surface of lens 16 and the first surface of lens 20. The .20 inch dimension listed in association with lens 20 is the thickness of that lens, the 1.04 inch dimension being the distance between the second surface of lens 20 and exit pupil 21.
It should be noted/ of course, that the dimensions and parameters listed in Tables 1 and 2 do not represent the present invention, but rather the dimensions and parameters of a system comprising the present invention.
1 ~2~6~
It should also be noted that, while the mangin mirror has been shown as a secondary mirror in the disclosed embodiment, the secondary mirror could be a front surface mirror, and the primary mirror could be a mangin mirror with first and second surfaces shaped for providing control of field curvature.
Alternately, both mirrors could be mangin mirrors with one or both having surfaces so shaped.
Further, although mirror 12 comprising the present invention is disclosed as aspheric see Table 1), a mangin mirror comprising the present invention may also be spherical.
In addition, while a mangin mirror in accordance with the present invention is shown implemented in a cassegrainian arrangement, such an implementation is illustrative only since a mangin mirror in accordance with the present invention may be applied in any optical system wherein radiation may be suitably received, refracted, and reflected by the mirror in order to control field curvature.
Finally, it should be noted that the present invention provides field curvature control. Such control may be desiyned to include only partial correction of field curvature, either without further correction provided by additional system optics or, as in the disclosed example, with further correction by additional system optics (collimator 15 in the disclosed system).
Alternately, the field curvature control provided by the present invention may be designed to completely correct field curvature introduced by other optics within a system.
J 1627~7 The present invention is to be limited only in accordance with the scope of the appended claims, since persons skilled in the art may devise o~her embodiments still within the limits of ~he claims.
.
Claims (19)
1. An optical element for providing control of field curvature, the optical element consisting of a mangin mirror comprising a lens having a first and a second surface, the second surface being coated with reflective material, the radiation received by the lens being refracted at the first surface, reflected back from the second surface, and then refracted once again by the first surface, the first and second surfaces having a shape for providing control of field curvature.
2. The apparatus of claim 1 wherein the mangin mirror is a secondary mirror.
3. The apparatus of claim 1 wherein the mangin mirror is a primary mirror.
4. The apparatus of claims 2 or 3 wherein the mangin mirror is aspheric.
5. An optical element for providing control of field curvature, the optical element consisting of a mangin mirror comprising a lens having a first and a second surface, the second surface being coated with reflective material, the radiation received by the lens being refracted at the first surface, reflected back from the second surface, and then refracted once again by the first surface, the first and second surfaces each having a radius defined by the equation 1/R = 2/n[n+1)/ r1 + 1/r2] where R is the radius of the field curva-ture, n is the index of refraction of the lens, rl is the radius of the first surface, and r2 is the radius of the second surface.
6. The apparatus of claim 5 wherein the power of the mangin mirror is 1/f and is defined by the equation 1/f = 2[n/r2 - (n-1)r1] wherein f is the focal length of the mangin mirror, n is the index of refraction of the lens, r1 is the radius of the first surface, and r2 is the radius of the second surface, whereby the radii of the first and second surfaces can be selected to provide any com-bination of focusing power and field curvature.
7. The apparatus of claim 5, wherein the mangin mirror is a secondary mirror.
8. The apparatus of claim 5 wherein the mangin mirror is a primary mir-ror.
9. The apparatus of claim 5, 7, or 8 wherein the mirror is aspheric.
10. An optical arrangement for providing control of field curvature, the arrangement comprising a lens having a first and a second surface, the second surface being coated with reflective material, the radiation received by the lens being refracted at the first surface, reflected back from the second sur-face, and then refracted once again by the first surface, the first and second surfaces having a shape for providing control of field curvature.
11. The apparatus of claim 1 wherein the lens is integral to a mangin secondary mirror.
12. The apparatus of claim 1 wherein the lens is integral to a mangin primary mirror.
13. The apparatus of claims 2 or 3 wherein the mangin mirror is aspheric.
14. An optical arrangement for providing control of field curvature, the arrangement comprising a lens having a first and a second surface, the second surface being coated with reflective material, the radiation received by the lens being refracted at the first surface, reflected back from the second sur-face, and -then refracted once again by the first surface, the first and second surfaces each having radii which determine the field curvature by the equation 1/R = 2[(n-1)/r1 + 1/r2]/n where R is the radius of the field curvature, n is the index of refraction of the lens, r1 is the radius of the first surface, and r2 is the radius of the second surface.
15. The apparatus of claim 14 wherein the power of the lens is l/f and is defined by the equation 1/f = 2[n/r2 - (n-1)/r1] wherein f is the focal length of the lens, n is the index of refraction of the lens, r1 is the radius of the first surface, and r2 is the radius of the second surface, whereby the radii of the first and second surfaces can be selected to provide any combination of focusing power and field curvature.
16. The apparatus of claim 15, wherein the lens is integral to a mangin secondary mirror.
17. The apparatus of claim 15, wherein the lens is integral to a primary mirror.
18. The apparatus of claims 14, 15 or 16, wherein the lens is aspheric.
19. The apparatus of claim 15, wherein the lens is integral to a primary mirror and the lens is aspheric.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US20553180A | 1980-11-10 | 1980-11-10 | |
| US205,531 | 1980-11-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1162767A true CA1162767A (en) | 1984-02-28 |
Family
ID=22762581
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000388929A Expired CA1162767A (en) | 1980-11-10 | 1981-10-28 | Field curvature control |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1162767A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107807441A (en) * | 2017-11-22 | 2018-03-16 | 中国科学院长春光学精密机械与物理研究所 | catadioptric optical imaging system |
-
1981
- 1981-10-28 CA CA000388929A patent/CA1162767A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107807441A (en) * | 2017-11-22 | 2018-03-16 | 中国科学院长春光学精密机械与物理研究所 | catadioptric optical imaging system |
| CN107807441B (en) * | 2017-11-22 | 2018-08-17 | 中国科学院长春光学精密机械与物理研究所 | catadioptric optical imaging system |
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