CA2192328A1 - High speed optical system - Google Patents
High speed optical systemInfo
- Publication number
- CA2192328A1 CA2192328A1 CA 2192328 CA2192328A CA2192328A1 CA 2192328 A1 CA2192328 A1 CA 2192328A1 CA 2192328 CA2192328 CA 2192328 CA 2192328 A CA2192328 A CA 2192328A CA 2192328 A1 CA2192328 A1 CA 2192328A1
- Authority
- CA
- Canada
- Prior art keywords
- lens system
- spherical
- concentric
- lens
- detector
- 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.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
- G02B17/08—Catadioptric systems
- G02B17/0884—Catadioptric systems having a pupil corrector
- G02B17/0888—Catadioptric systems having a pupil corrector the corrector having at least one aspheric surface, e.g. Schmidt plates
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
- G02B17/08—Catadioptric systems
- G02B17/0804—Catadioptric systems using two curved mirrors
- G02B17/0808—Catadioptric systems using two curved mirrors on-axis systems with at least one of the mirrors having a central aperture
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
- G02B17/08—Catadioptric systems
- G02B17/082—Catadioptric systems using three curved mirrors
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
- G02B17/08—Catadioptric systems
- G02B17/0836—Catadioptric systems using more than three curved mirrors
- G02B17/084—Catadioptric systems using more than three curved mirrors on-axis systems with at least one of the mirrors having a central aperture
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B17/00—Systems with reflecting surfaces, with or without refracting elements
- G02B17/08—Catadioptric systems
- G02B17/0852—Catadioptric systems having a field corrector only
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Lenses (AREA)
- Telescopes (AREA)
Abstract
The present invention provides a lens system and/or a method of imaging onto an imaging detector. The lens system and method are used in focusing substantially parallel incident light onto the said detector. The lens system comprises: (a) a concentric spherical Cassegrain-like system of two mirrors; (b) a concentric spherical focal reducer; (c) a transfer lens system which combines the concentricity of the Cassegrain-like system of two mirrors and of the concentric spherical focal reducer by imaging the first centre of concentricity that is of the system of two mirrors onto the second centre of cencentricity, that is, of the focal reducer to thereby provide a single optically cencentric system which combines their advantages. Also present in the system are: (d) means to correct the sum of the spherical aberation of all the spherical mirros in the entire system and (e) an aperture stop.
Description
WO 95/34013 r~ .7s ~
2i~23~8 "HIGH SPEED OPTICAL SYSTEM"
TECHNICAL FIELD
This invention relates to an optical lens system and, optionally, an 5 associated optical relay.
BACKGROUND ART
Solid state imaging alrays (CCDs, ClDs, etc) have now become the sensors of choice in many ~ Being planar, ~ 11y accurate (to the limit of Illh,lulilllo~, . ' y t~,. ' -' -~) and with a high quantum efficiency in the10 visible and near-infrared spectral domains, such devices have the potential to be vir~ually perfect image detectors.
For the pulpose of low-light-level imaging or aall~h~ with CCD
devices, the ill ,ll .l.ll~,.ll designer's problem is to find an optical system with a matching ~. . r,..,~ not only in ~ IJI;..--~l resolution and distortion 15 cLalP~ c but also in speed so as to achieve the highest possible r _~ rate. However, when aperture diameters exceed 150mm, the J of optical glass becomes an intrusive problem and design solutions usually reduce to catoptric or c ' -~ ; - systems which gcnerally require only one refractive , of the full aperture diameter.
Few such systems exist which combine the ,1 -- P ~ of high speed (eg. faster than f/4) and high - amd uniform - resolution to the ~' 1 limit required by CCD pixel structures. If, to these notional L ~, there are added such pragmatic aspects as ease of r ~ ' " and moderate ~1. the list of suitable designs tends toward zero length.
The top of the list is occupied by the Schmidt camera and its ~ a iaLi~
however, as desigr~ tend towards higher speed and urliform flattened-field resolution, the 1; . ;f~ of the full-aperture aspheric corrector become evident in the form of more difficult and expensive rP~
residual sphero-chromatic aberration and obliquity effects.
Maksutov camera designs also suffer from problems associated with their massive full-aperture thick meniscus corrector r.( 1 ~; to such an extcnt that -2 1 ~ 2 3 2 8 -2- P~
the advantage of smaller obliquity effects is overridden by high-order sphero-.,L~ la.i~ as the design speed is increased.
An additional obstacle which some low-light-level desigms must sunnount is the need to r-- ~ ' ' a clyostat for the CCD. Ideally this requires that the 5 focus be accessible externally, which in turn i~nplies a 1'~ ~ system, or atIeast a folded for~nat.
We ~ g., commonly owned New Zealand Patent Arrli~ ~tin~ No.
2363071236308 and Japanese Patent ~ppli~- No. JAP 4-185640 published as 6-82699. This invention relates to I U..,~ to the system.
This invention is an optical design which is novel in its assembly of mto a format that fits a ~ v;~ - , ' area of the speedldiameter r~ ti( ' ., and which u.~l..U ._s the problems previously OnP~ Fl ' ~;, preferred forms of the present invention provide a high speed optical system of economic _ or which, at least, provides the 15 public with a useful choice.
DISCLOSURE OF T~lE INVENTION
Ac.,uldil.~ the present mvention may broadly be said to consist in a lens system suitable for focusing ' -'ly parallel incident light onto â detector, said system (A) a concentric spherical (' ~, Iike system of two mirrors, (B) a concentric spherical focal reduca, (C) a transfer lens w~ich combines the ~ of the C ~, like system of two rnirrors amd of the concentric spherical focal reducer by i]naging the first centre of _ ~/ (that of the system of two mrrrors) on the second centre of c.,.. .,l"~ ;1y (that of the focal reducer) to thereby provide a sirlgle optically conccntric system which combmes their aJ ~ ~ .
(D) means to correct the sum of the spherical aberratio~ of all of the spherical mr~rors in the entire system, and (E) anape~ure stop.
2i~23~8 "HIGH SPEED OPTICAL SYSTEM"
TECHNICAL FIELD
This invention relates to an optical lens system and, optionally, an 5 associated optical relay.
BACKGROUND ART
Solid state imaging alrays (CCDs, ClDs, etc) have now become the sensors of choice in many ~ Being planar, ~ 11y accurate (to the limit of Illh,lulilllo~, . ' y t~,. ' -' -~) and with a high quantum efficiency in the10 visible and near-infrared spectral domains, such devices have the potential to be vir~ually perfect image detectors.
For the pulpose of low-light-level imaging or aall~h~ with CCD
devices, the ill ,ll .l.ll~,.ll designer's problem is to find an optical system with a matching ~. . r,..,~ not only in ~ IJI;..--~l resolution and distortion 15 cLalP~ c but also in speed so as to achieve the highest possible r _~ rate. However, when aperture diameters exceed 150mm, the J of optical glass becomes an intrusive problem and design solutions usually reduce to catoptric or c ' -~ ; - systems which gcnerally require only one refractive , of the full aperture diameter.
Few such systems exist which combine the ,1 -- P ~ of high speed (eg. faster than f/4) and high - amd uniform - resolution to the ~' 1 limit required by CCD pixel structures. If, to these notional L ~, there are added such pragmatic aspects as ease of r ~ ' " and moderate ~1. the list of suitable designs tends toward zero length.
The top of the list is occupied by the Schmidt camera and its ~ a iaLi~
however, as desigr~ tend towards higher speed and urliform flattened-field resolution, the 1; . ;f~ of the full-aperture aspheric corrector become evident in the form of more difficult and expensive rP~
residual sphero-chromatic aberration and obliquity effects.
Maksutov camera designs also suffer from problems associated with their massive full-aperture thick meniscus corrector r.( 1 ~; to such an extcnt that -2 1 ~ 2 3 2 8 -2- P~
the advantage of smaller obliquity effects is overridden by high-order sphero-.,L~ la.i~ as the design speed is increased.
An additional obstacle which some low-light-level desigms must sunnount is the need to r-- ~ ' ' a clyostat for the CCD. Ideally this requires that the 5 focus be accessible externally, which in turn i~nplies a 1'~ ~ system, or atIeast a folded for~nat.
We ~ g., commonly owned New Zealand Patent Arrli~ ~tin~ No.
2363071236308 and Japanese Patent ~ppli~- No. JAP 4-185640 published as 6-82699. This invention relates to I U..,~ to the system.
This invention is an optical design which is novel in its assembly of mto a format that fits a ~ v;~ - , ' area of the speedldiameter r~ ti( ' ., and which u.~l..U ._s the problems previously OnP~ Fl ' ~;, preferred forms of the present invention provide a high speed optical system of economic _ or which, at least, provides the 15 public with a useful choice.
DISCLOSURE OF T~lE INVENTION
Ac.,uldil.~ the present mvention may broadly be said to consist in a lens system suitable for focusing ' -'ly parallel incident light onto â detector, said system (A) a concentric spherical (' ~, Iike system of two mirrors, (B) a concentric spherical focal reduca, (C) a transfer lens w~ich combines the ~ of the C ~, like system of two rnirrors amd of the concentric spherical focal reducer by i]naging the first centre of _ ~/ (that of the system of two mrrrors) on the second centre of c.,.. .,l"~ ;1y (that of the focal reducer) to thereby provide a sirlgle optically conccntric system which combmes their aJ ~ ~ .
(D) means to correct the sum of the spherical aberratio~ of all of the spherical mr~rors in the entire system, and (E) anape~ure stop.
3 2 1 ~ ~ 3 2 8 P1,1,~
1 _3_ Preferably said lens system further includes:
(F) image detection means (hereafter "detector") at the focus of the focal reducer.
Preferably said concentric spherical r~ like syste}n of two mirrors 5 does not mclude any aperture stop.
Preferably said concentric spherical focal reducer includes at least one spherical mirror element.
Preferably said concentric spherical focal reducer includes at least one refractor element.
Preferably said tramsfer lens system is a refractive simgle lens.
Preferably said concentric spherical focal reducer is selected from the group c~
i. Modified forms of Baker camera;
ii. Modified form of Hawkms and Linfoot camera;
iii. Derivation of Maksutov or Bouwers camera.
Preferably said concentric spherical focal reducer is a modified form of the Hawkins and Linfoot camera system and said means to correct the sum of the spherical aberration of all of the spherical mirrors in the entire system and said aperture stop forms part thereof.
Preferably said means to correct the sum of this spherical aberration of all of the spherical mirrors in the entire system is a concentric meniscus ~
with the c ~ ~ focal reducer.
Preferably the chromatic aberration i~ . ' ,e d by the said c~ .. .- 1, ;-meniscus is , ' by a refractive c ~ located at the aperture stop.
Preferably said refractive c ~ is a zero-power chromatic le~s or lens cclmh;~ ;nn, for example, a doublet lens or lens: ' Alt~ dti~ly said refractive ~---r ' is a weakly positive power simglet lens.
Preferably said zero power refractive - . mcludes an aspheric zonal 30 corrector surface ~ 1l~, weak not to introduce any ~ degree of WO95/34013 21~328 1~1,..~5~ -focal ~ when instant light is angled into the overall lens system other than axially.
Preferably said lens system is ' lly faster than f/l.
Preferably said lens system is about f/0.8.
Preferably said detector is included.
Preferably said detector is a solid state detector.
Preferably said detector has a ' lly planar detection surface.
BRIEF DESCRIPTION OF T~E DRAWINGS:
Figure I shows a speed size ~ for a~ including an 10 P...l~.l;.. ..~ of the invention;
Figure 2 is a drawing of prior art concentric ~ CP~in Schmidt or Maksutov cameras;
Figure 3 is a drawing of one preferred; ' - ' of the present invention;
Figure 4 is a ~ ~c~,live sectional drawing of am optical relay optionally 15 for~ung part of the invention;
Figure 5 is a p~,.~.,~Lv~ sectional drawing of one preferred C~ " of the present mvention;
Figure 6 is a profile of the asphere of a preferred; ' ' of the present invention in a,~ul~.,c with Example l;
Figure 7 is a cross-sectional, side elevation view of the system of Example l;
Figure 8 is a graphical illllclTP*rm of the ~,~ . r....-- -- . of the system of Example 1;
Figure 9 is a cross ..~,Liu..dl, side elevation view of the system of Example 25 2;
Figure 10 is a graphical illllcfrP*~n of the I r e of the system of Example 2;
Figure 11 is a cross-sectional, side elevation view of the system of Example 3;
Figure 12 is a ~l~c~,live sectioned view of an altemative forln of the relay which includes a concentric window for a cryostat;
WO 95134013 ~ ~ ~ 2 ~ ~ ~ r~
Figure 13 is a graphical illllcf~rpfir)n of the ~ r. ~ of the system of Example 3; and Figures 14a, 14b amd 14c are ill--ef.~fior ~ of prior art Maksutov, Baker arld Hawkins ~ Linfoot cameras which cam be modified to provide concentlic 5 spherical focal reducers in a preferred for~n of the mvention.
DETAILED DI~SCRIPTION OF TEIE INVENTION:
Preferred forms of the present invention is a concentric 1~ Iike system with a focal reducing relay, all critical surfaces being spherical. The relay described herein is also a concentric system amd provides the f/l speed 10 ~ l\ L .'' .~' '; ` ;~' at an external focus, but it should be noted that other relays can be used to give different speed/image-scale l Figure I shows the ranges of apertures amd speeds for which the named design types are a~ylul This invention is a~ , for the area named "new zone".
The star ing point for the concept ' ip~ is the concentric ~`~eel~
Schmidt or Maksutûv camera designs shown a3 filt.,.l.aLi~,~,i. in Figure 2. These include am aperture stop 23, a primaly mirror 24, a secondary mirror 25 and a focal surface 26. Apart from obliquity effects in the Schmidt asphelic corrector21 or high-order sl L,.. ' , in the Maksutov corrector 22, fhe irnage 20 quality of these designs is uniform over the whole field. The Schmidt corrector, located at the common centre of curvature of the mirrors and which fills f he aperture stop, has am axis of symmet~y, as does the Maksutov meniscus in its a~,L~Iudtic forms. The 5 ' ~; penalties of these designs are the need for a r~ 3~ : i aspheric or for a full 1, thick meniscus corrector amd the 25 length of the structure or tube required to support the corrector.
Referring now to Figure 3, if the corrector is omitted from these designs but the aperture stop left in position, at the common centre of curvature of the mirrors, the obvious result is the i~lfuuuh.~,livll of severe spherical aberration at all field angles. If, now, a field lens is iulludu~,c~ near the ~c~ grai~l focal position, 30 an image of the aperture stop amd of the common centre of curvature of the mirrors is created further behind the primary mirror 31. If a real aperture stop 32 WO 95134013 2 1 ~ ~ 3 ~ 8 is located coincident with tbis image, tben it is axiomatic that the function of the classical Schmidt aperture stop (flf ~ of the marginal rays at all field ~ngles), is ' l l d, so that the classical stop can be ' ' The cornmon centre of curvature of the mirrors, and the classical aperture stop have been 5 optically t~lu~L.~c~ to the new location. An immediate advantage is the reduction of the camera length to about the same dimension as the y/~e~,u--v~y SPp~tif n The spherical aberration can then be colrected by insertion of a merliscus . 33 concentric with the centfe of the new aperture stop 32, as this is now a new centre of ~ y 34 optically 10 u~ ,d from the classical Schmidt location. This transfer of the centre of c.... .,1. ;.:ly is the prime function of the field lens 35, so is terme~ the transfer lens in the remainder of this ~
Note that the r~P~.n focus is relocated to a position between the two mirrors 31 and 37; the optical train is shortened overall by the small forward shift 15 of the secondary rrurror 37. The corrected image is virtual and is located at 36, between the relocated "cassegrain" focus and the correcting meniscus 33, becauseof the net negative power of the latter. To l~ ~l,L ,L a real image requires a relay lens which should, of course, be placed with its entrance pupil ~.;, .:.1. ., with the aperture stop. Clearly, numerous cr~rifif - could be derived for 20 relay lenses with differing conjugate ratios; the relay to be described here can reduce the relatively large virblal image to the ~' typical of CCD
devices, and shares the c~ Y ~ r~ ,~ of the preceding optics, thus retaining the essential ~ l ' from off-axis ~
Fast focal reducers are well known adducts for "slow" telescopes and small 25 detector devices, but in this invention an unusually cou~.,.~ivc melding is possible between the subsystem described ~ ;vu ,l~ and the type of focal reducing relay shown in Fig. 4. The concentric meniscus 44 provides correction of the spherical aberration of the concave spherical mirror; --l- ~ ly of field angle ir~ the same manner as described previously for the basic inventions 30 ,ul~y wo 95/34013 21 Q 2 3 2 8 ; r~
The doublet 45 is afocal and mtroduces a chromatic error equal and opposite to the chromatic error of the meniscus 44. Bemg located at the aperturestop, doublet 45 acts equally on all ray bundles so does not disturb the overall ~ y of the system.
It should be noted that there are two physical centres of curvature in Fig. 4.
The centre of the aperture stop 45 is the centre of curvature of the meniscus 44, but tbis centre is reflected to the position 40 by the folding flat 46. This r -~ makes it possible to achieve an external focus for greater ~C~ y, Field curvature is inherent in concentric designs, as is well known in Schmidt cameras especially, and can be corrected by the insertion of a field flatterling lens 48 close to the focal surface, but, at least in the usual Schmidt ~. ~ " . ~ , only at the expense of Ulll. ' g c~ off-axis .? ",,, ~ ;"
However, as the numerical aperture (the speed) is increased, tbis problem is at 15 least partially offset by the smaller scale of the focal surface geometry. In the cl.lbc ' described in t~?is ~rçrifj~ the field flatterling lenses are so weak as to add no ~ ;..- to the residua~ sphero-chromatic blur.
By merging the aperture stop of the relay and the ll~.~f~ aperture stop of the new subsystem, the fast imaging system is ' ' ~
Figure 5 shows the layout resulting from the merge with ' ' rays shown at a typical off-axis angle in this example at 1.83 degrees offaxis. The system has a primary mirror 51 and a secondary mirror 52. The system also mcludes a corrector group 54 and 55 (the ~ l v ' of meniscus 44 and doublet 45 in Fig 4) and a folding flat 56.
Also visible m Figure 5 is the small weak field flattener 58 wllich delineates the final f~at focal surface. In this particular design, the field flattener lens 58 is intended to be optically cemented to the otherwise .~,..,d silicon - structure of the CCD detector. This minimises additional ~l~tir~nc c,by the field flattener 58 and serves to protect the CCD surface from 30 c Separation of this lens from the focal surface would cause it to intrude too far into the f/l ray cone with implicit degradation of the image sharpness.
As shown in the system in Figure 5, the ~ r `~ C of this system can be ' as:
(a) the focal power resides in the mirrors~ and so is non-chromatic.
(b) the spherical mirrors are optically c, thus ~ ;..,o. coma amd ~ when the aperture stop is located at the centre of curvature (or at the optical equivalent).
(c) spherical aberration correction is the only remaining necessary 10 adjunct to the reflective optical elements. This is the function of the corrector group.
(d) the residual a~h are 1.,.. ~rlih..iP C~ ti~mc of secondary colour with weak higb-order coma and r-'i,., ' , generated primarily at the non-concentric surfaces of the transfer lens.
(e) vignetting is minimal. The central obsc~ht~r~ is ,l. ~. . .- -~;1 by the pprfr~h~nc in the folding and relay mirrors, provided that the design is adjusted so as to image the seconda~y n~irror mto the space between them. In Example I
below, tbe central ~ ,.,. is about 31.2% on axis, increasing to 33% at the ~ill r ~ e ofthe llmmdiameterimage.
(f) distortion is rninimal, witb an amplitude generally less than that of the blur spot ' To min~mise future r~ costs, the example designs make use of "Smith's List" of workshop tool radii for the radii of curvature of the optical Although non-optimum for residual aberration - - - . the 25 difference in ~.. r.. - .~-e is ~ecligible.
The tbree following examples d--- very different variants of the basic design, a 200mm aperture f/0.9 visible/NlR, a lOOOmm aperture f/0.8 visible/NIR amd a 200mm aperture f/0.93 thermal infrared version.
The cl.~ .; r;- ~ ;.... tables are based on a coordinate system in which the z-30 axis is the optical axis and the x and y-axes are mutually Ul ILOC~ to it. Inthese design examples the origin is tbe centre of curvature of the primary rnirror.
W0 95/34013 ~ l a ~ 3 2 ~ r~
_9_ "Diarn" and "diam" are the outside and inside diameters of annuli. The shape of the aspheric trimmer profile is defined by the polyllvll.ial equation: z = c.x2/2 +
a2.x~ + a6.x6 + a8.x8 where c is the curvature, x is the x-coordinate arld a~ are the coPffi -The bandpass for the first two of the examples given for this class of the system is intended to match the spectral sensitivity of generic silicon CCD
devices, for which the highest response lies between 450 and l lOOnm. The Cull~_r ' V refractive index data for optical glass is published for the spec~allines g, e, d, C, r, s and nl060 0 amongst others, providing a good coverage for10 analytic purposes.
The initial ray-tracing process always shows some coma as the dominant residual P~P~rP~inn for off-axis rays, emanating from the non-concentric c, , This is largely corrected by illL-. ' v equal and opposite coma within the concentric ('~Ccp~ subsystem, the technique chosen here being that 15 of increasing the focal length of the transfer lens so as to make the tr~msfer illll.~,lrt;.,lly cu -. rhe effect of this procedure is to displace the centre of the entrance pupil away from the classical Schmidt location (at the centre of curvature of the primaly mirror), and laterally ,UIU~Ol ' to off-axis angle, thus effecting the required c~ Ray tracing is perfoImed thereafter by 20 ensuring that the aperture stop, located at the aspheric surface, accurately delineates the marginal rays for each spectral line.
The median ray aberration graphs which follow, have as their vertical axis the height of the ray in the entrance pupil and the horizontal axis gives the lateral position of the intercept with the focal plane.
The 2D l,;~ are ~ d in , ' ', any ';v~ fine structure is derived from the line-spectrum ray trace. The most relevant feature is the maximum extent of the "ru~l~lilli" on the 32 Y 32~1m focal patch.
Wo95134013 21g~8 ~ ~5~
Surface Glass Z(verte~) Cur~ature Radius Surface Type diam Diam 0 618 Obstruction 95 5 1 1016 -0.00098425 -1016 ~irror 8S 25S
2 633.5 -0.00157853 -633.5 ~irror 92 3 830 0.0046904 213.2 ens 55 4 SK 11 848 -0.00~2549 -190.3 _ens 55 1009.45 0.01619433 61.75 ens 60 10 6 SK 4 iO29.27 O.OZ384927 41.93 ens 60 7 1065 0 fla~ ens 56.5 8 F 4 1071 -0.0072275 -138.4 .ens 56.5 9 SK4 1075 0 lla~+asph .ens(S~op) 56.5 1143.6 0 fla~ dirror 47 105 15 11 1065 0.00679348 147.2 ~irror 60 150 12 1163.67 0.03298915 30.31 ens 12 13 SF2 1164.67 0 flat ocus IZ
Aspheric CoefficieDts of Surface 9 Entrance Pupil ~iam. = 200m A2 -5.50E-05 Focal Length = 173.Zmm 20 A4 1.281E-07 Geometrical Focal Ratio = 0.87 A6 -5.878E-II CeDtral obscura~ioD = 31.2%
A8 -2.184E-14 BaDdDass = 436Dm ~o 1060Dm The profile of the aspheric zonal corrector surface is illustrated in Fig. 6.
25 Note that the z-axis is expanded by a factor of 2000 relative to the (vertical) x-axis. Fig. 7 provides a side elevation of this example design, Fig. 8 gives a graphical ilillc~r?~inn of the computed F ~ ' The ' ' ray aberration curves in Figure 8, d~ moderate stability, with no tendency to chaotic extremes as the field angle is increased. As 30 the 2D l~ show, all the ene}gy from 436 to 1060nm is focused into only part of ~e 32 X 32,um focal area even at 1.4SS off axis (the angular radius CUII~,a~lld;~g to the side of the 7 X 9mm - or "2~ inch" video-standard image).
WO95/34013 21~232~ P-ll L s~
Surface Glass Zlvertex) Curvature Radius Surface Type diam Diam o 3550 Obstruction 250 6000 -0.0001667 -6000 Mirror 1045 5 2 3575 -0.0002797 -3575 Mirror 250 3 4401 0.0065004 144.9 Lens 62 4 F 4 4407 0.0187758 53.26 Lens 62 5 SK 4 4419 -0.0004764 -2099 Lens 62 6 4580.5 0.01619433 61.75 Lens 58 10 7 SK 4 4602.25 0.025 40 Lens 58 8 4636 0 flat Lens 55 9 F 4 4642.25 -0.0085063 -117.6 Lens 55 10 SK 4 4646 0 flat l asph Lens(Stop) 54.6 11 4793.2 -0.0067935 -147.2 Mirror 155 15 12 4693.241 -0.03365497 -27.36 Lens 14 13 SF 2 4692.241 0 flat focus 14 Aspheric ~ '~ of Surface 10 Entrance Pupil Diam. = 1000rnm A2 = -9.6E-05 Focal Len~th = 814.8mm A4 = 2.206E-07 Geometrical Focal Ratio = 0.82 20 A6 = -9.976E-11 Entral Obscuration = 6.3%
A8 = -3.1 59E-14 Bandpass ~ 436nm to 1 060nm At EPDs i" ~ 'y greater than lm, - on the new design systcm are imposed by the greater scale of spherical aberration at the c-25 (~5~CC~ in focus, which gencrates ~ r errors of mapping of the idealentrance pupil onto the system aperture stop by the transfer lens. The resulting high-order ~ -- tend to exceed 9~C~ ' levels relative to the pixel .1: ,. . i ...~ of the d~l~. CCD detectors.
Example 2 describes a lOOOmm aperture version. There is an extra 30 chromatic correction element used in the transfer lens of the lm variant. This helps to tr.im back the outer parts of the blur spot which are caused by the extremes of the spectral bandpass.
Figure 9 shows the side view of the optical layout and Figure 10 gives a graphic illl-cfra~ion of the computer median ray and blur spot ~, c( WO95/34013 ~1~2~28 ~..~sc~- l T~RMAT. INFRARl~D VARIANT
It is clear that other regions of tbe spect~um can be utilised, given the ~)~JIUI ' detectors and refractive media to which this design principle can beadapted. In recent years, arrays of thermal infrared detectors have been 5 fabricated, tbe most useful in the context of the new imaging system being ~e Pt:Pt-Si CCD arriys that are now ~ lly available. With useful spectral sensitivity in the spectral domain 3.5 - 5.5~m, these detectors have overall andpixel ,~ ".~ similar to those of the normal visible/~lR silicon irnagers.
Moreover, in the 3.5 - 5.5~m spectral domain, ~e is a low-cost, 10 easily worked optical medium suited to the refractive ~ . . of the fast relay, with the benefit that the high refractive index allows large .~ in the spherical curvatures of the field/transfer lens giving a c~ l,lhlg ~ r;~
reduction of the high-order ~ .. ".l ;....~ which limit the off-axis p.. r... ~ ., - e of the visible/NIR version of this design.
wo 9S/34013 21~ 2 3 2 8 F~
Surf ce Gl-~ Z(verte2~) Curv~ture RldiU~ Smf ceType di-m Di-m - o 620 Obstruction 88 1000 -0.002 -1000 ~or 80 260 5 2 62s -0.0016 -625 ~ror 88 3 836.31 0.001523 6s6.6 Lens s4 4 Ge 846.31 o flnt Lens s4 s 1082.11 0.01727414 s7.ss Lens 70 6 Ge 1089.35 0.01974334 5065 Lerls 70 10 7 1135 0.00021 4761.9 Lens 70 8 AL2o, 1140 o flat+asph Lens (stop) 70 9 1232.5 o flat M~r s3 125 o 1125 o.oos 200 Mirror 7s 180 Il 1244.13 0.01236553 80.87 Lens 33 15 12 Ge 1248.41 0.0130s6s4 76.ss Lens 33 .374 0.024s7032 46.36 Lens 12 o~ 1261.374 o ~dat iOCUs 12 ~-pheric coemdent~ o~ Surf~ce g Erltra~ce Pupil Diam. = 1 s6mm A2 -I . ~4E-05 Focal Le~lg h = 181 .2mm A4 5 . 1 9E-08 Geometrical Foc21 F~ho = 0.93 A6 -I .03E-1 I Central obscuration = 29%
A8 -g.OOE- I s sandpass = 3.7 - 5.5L m The table of Example 3 lists the optical desigil of a thermal version of the 25 new system, . . ' I - in most . ~ to those of the example given in Table 1. Figure 11 shows the side view of t~te optical layout.
The ~;~ .. I; ~ Lff~ m detail mclude the use at the aper~ure stop of a syntbetic sapphire spectial dispersion corrector I IS which has only a singlet format, but which has a weak positive power exactly sufficient for the ~
30 positive 1 ~ ' I c~tromatic aberration to correct the negative chromatic aberration of the ~. concentiic meniscus corrector over the spectral band 3.7 - 5.5,um.
WO95134013 2~g2328 r~".,~
An essential c, , of a thermal camera of this type is the cryostat sub-system. The cryostat wirldow is usually made as arl optical flat, but with the fast optics in this design, it is more ~ , to fabricate the window as a concentric meniscus 119 with its centre of curvature coincident with the 5 re~ectiorl of the common centre of culvature created by the folding flat. A
pvlayvvLvr view is shown in Fig. 12. This window then ' to tbe corrective negative spherical aberration of the system and introduces no off-axis 9~
Figure 13 illustrates the computed ~ of the mediarl ray bundles 10 and of the blur spot.
A possible advantage of at least preferred forms of the present invention over prior art designs such as provided by the Hawkins and Linfoot camera as thebasis for the design of the focal reducmg relay, is that the corrector meniscus is truly c : v, and the chromatic doublet has zero power, thus giving more 15 degrees of freedom to the designer. The classical Maksutov corrector is designed a~ ;L~ non-cr~nc~1Tir~ so asto lly . , forits chromatic aberration for small angles off axis; however, it is believed that at least preferred forrns of the present invention exceed allowable off-axis arlgles irl this case.The extra degrees of freedor~ ~ above can be used to 20 a~Oclu~ the system, in that optical glasses can be selected for the meniscus and the chroma~ic doublet which permit a sharp focus for more than the usual two ~a~ implicit in the usual - ', - correction.
~ perifir~lly, by choosing Schott FK 51 for the meniscus, the chrornatic aberration to be corrected by the doublet is !~ to the extent that the 25 glasses KzF N2 and PK 5 la can be utilised to provide a~cLl over the bandpass 400 to 1 lOOnm (the entire sensitive bandpass of typical silicon-based CCD imaging devices), while retaining the zero-power qleri~rs*~ of the doublet. A triplet form allows even further gains in aberration control.
The result of this is that the resolution of the system is improved by a factor 30 of a~ y 3, with blur-spot ~ potentially as low as 5 llf~ lvh~va over the entire image area, at speeds of the order of flO.8 and for the 2~92328 WO 95134013 r~ ,s.C~~~
bandpass ~ n~in-~d above. This, in turn, implies the ability to scale up tbe design so as to q~cn~ ' the newer very large silicon CCD imaging devices now coming into use in .~tl~ ' and other scientific research.
SCALING
All three examples given here are based on the use of a "Z~mch" video standard CCD detector, which effectively ~ the linear ~' of the fast relay sub-system for a specified Numerical Aperture. Other detector may require ",~ ;.... of the relay to provide the a~ U~ ' ' of speed, linear field at the fieldlt~ansfer lens, and residual 10 aberration blur.
From the three examples it can be seen how, once the d~,t~.lul/ll,l~
cnnlh;-qtinn has been initially ~ ~, the Cqecpgr~qin can then be ~ which will match the required object field a~gle to the linear field of the relay. Melding of the two sub-systems is then achieved by detailed 15 q~lq,rtqti~n of the fieldltrnsfer and corrector
1 _3_ Preferably said lens system further includes:
(F) image detection means (hereafter "detector") at the focus of the focal reducer.
Preferably said concentric spherical r~ like syste}n of two mirrors 5 does not mclude any aperture stop.
Preferably said concentric spherical focal reducer includes at least one spherical mirror element.
Preferably said concentric spherical focal reducer includes at least one refractor element.
Preferably said tramsfer lens system is a refractive simgle lens.
Preferably said concentric spherical focal reducer is selected from the group c~
i. Modified forms of Baker camera;
ii. Modified form of Hawkms and Linfoot camera;
iii. Derivation of Maksutov or Bouwers camera.
Preferably said concentric spherical focal reducer is a modified form of the Hawkins and Linfoot camera system and said means to correct the sum of the spherical aberration of all of the spherical mirrors in the entire system and said aperture stop forms part thereof.
Preferably said means to correct the sum of this spherical aberration of all of the spherical mirrors in the entire system is a concentric meniscus ~
with the c ~ ~ focal reducer.
Preferably the chromatic aberration i~ . ' ,e d by the said c~ .. .- 1, ;-meniscus is , ' by a refractive c ~ located at the aperture stop.
Preferably said refractive c ~ is a zero-power chromatic le~s or lens cclmh;~ ;nn, for example, a doublet lens or lens: ' Alt~ dti~ly said refractive ~---r ' is a weakly positive power simglet lens.
Preferably said zero power refractive - . mcludes an aspheric zonal 30 corrector surface ~ 1l~, weak not to introduce any ~ degree of WO95/34013 21~328 1~1,..~5~ -focal ~ when instant light is angled into the overall lens system other than axially.
Preferably said lens system is ' lly faster than f/l.
Preferably said lens system is about f/0.8.
Preferably said detector is included.
Preferably said detector is a solid state detector.
Preferably said detector has a ' lly planar detection surface.
BRIEF DESCRIPTION OF T~E DRAWINGS:
Figure I shows a speed size ~ for a~ including an 10 P...l~.l;.. ..~ of the invention;
Figure 2 is a drawing of prior art concentric ~ CP~in Schmidt or Maksutov cameras;
Figure 3 is a drawing of one preferred; ' - ' of the present invention;
Figure 4 is a ~ ~c~,live sectional drawing of am optical relay optionally 15 for~ung part of the invention;
Figure 5 is a p~,.~.,~Lv~ sectional drawing of one preferred C~ " of the present mvention;
Figure 6 is a profile of the asphere of a preferred; ' ' of the present invention in a,~ul~.,c with Example l;
Figure 7 is a cross-sectional, side elevation view of the system of Example l;
Figure 8 is a graphical illllclTP*rm of the ~,~ . r....-- -- . of the system of Example 1;
Figure 9 is a cross ..~,Liu..dl, side elevation view of the system of Example 25 2;
Figure 10 is a graphical illllcfrP*~n of the I r e of the system of Example 2;
Figure 11 is a cross-sectional, side elevation view of the system of Example 3;
Figure 12 is a ~l~c~,live sectioned view of an altemative forln of the relay which includes a concentric window for a cryostat;
WO 95134013 ~ ~ ~ 2 ~ ~ ~ r~
Figure 13 is a graphical illllcf~rpfir)n of the ~ r. ~ of the system of Example 3; and Figures 14a, 14b amd 14c are ill--ef.~fior ~ of prior art Maksutov, Baker arld Hawkins ~ Linfoot cameras which cam be modified to provide concentlic 5 spherical focal reducers in a preferred for~n of the mvention.
DETAILED DI~SCRIPTION OF TEIE INVENTION:
Preferred forms of the present invention is a concentric 1~ Iike system with a focal reducing relay, all critical surfaces being spherical. The relay described herein is also a concentric system amd provides the f/l speed 10 ~ l\ L .'' .~' '; ` ;~' at an external focus, but it should be noted that other relays can be used to give different speed/image-scale l Figure I shows the ranges of apertures amd speeds for which the named design types are a~ylul This invention is a~ , for the area named "new zone".
The star ing point for the concept ' ip~ is the concentric ~`~eel~
Schmidt or Maksutûv camera designs shown a3 filt.,.l.aLi~,~,i. in Figure 2. These include am aperture stop 23, a primaly mirror 24, a secondary mirror 25 and a focal surface 26. Apart from obliquity effects in the Schmidt asphelic corrector21 or high-order sl L,.. ' , in the Maksutov corrector 22, fhe irnage 20 quality of these designs is uniform over the whole field. The Schmidt corrector, located at the common centre of curvature of the mirrors and which fills f he aperture stop, has am axis of symmet~y, as does the Maksutov meniscus in its a~,L~Iudtic forms. The 5 ' ~; penalties of these designs are the need for a r~ 3~ : i aspheric or for a full 1, thick meniscus corrector amd the 25 length of the structure or tube required to support the corrector.
Referring now to Figure 3, if the corrector is omitted from these designs but the aperture stop left in position, at the common centre of curvature of the mirrors, the obvious result is the i~lfuuuh.~,livll of severe spherical aberration at all field angles. If, now, a field lens is iulludu~,c~ near the ~c~ grai~l focal position, 30 an image of the aperture stop amd of the common centre of curvature of the mirrors is created further behind the primary mirror 31. If a real aperture stop 32 WO 95134013 2 1 ~ ~ 3 ~ 8 is located coincident with tbis image, tben it is axiomatic that the function of the classical Schmidt aperture stop (flf ~ of the marginal rays at all field ~ngles), is ' l l d, so that the classical stop can be ' ' The cornmon centre of curvature of the mirrors, and the classical aperture stop have been 5 optically t~lu~L.~c~ to the new location. An immediate advantage is the reduction of the camera length to about the same dimension as the y/~e~,u--v~y SPp~tif n The spherical aberration can then be colrected by insertion of a merliscus . 33 concentric with the centfe of the new aperture stop 32, as this is now a new centre of ~ y 34 optically 10 u~ ,d from the classical Schmidt location. This transfer of the centre of c.... .,1. ;.:ly is the prime function of the field lens 35, so is terme~ the transfer lens in the remainder of this ~
Note that the r~P~.n focus is relocated to a position between the two mirrors 31 and 37; the optical train is shortened overall by the small forward shift 15 of the secondary rrurror 37. The corrected image is virtual and is located at 36, between the relocated "cassegrain" focus and the correcting meniscus 33, becauseof the net negative power of the latter. To l~ ~l,L ,L a real image requires a relay lens which should, of course, be placed with its entrance pupil ~.;, .:.1. ., with the aperture stop. Clearly, numerous cr~rifif - could be derived for 20 relay lenses with differing conjugate ratios; the relay to be described here can reduce the relatively large virblal image to the ~' typical of CCD
devices, and shares the c~ Y ~ r~ ,~ of the preceding optics, thus retaining the essential ~ l ' from off-axis ~
Fast focal reducers are well known adducts for "slow" telescopes and small 25 detector devices, but in this invention an unusually cou~.,.~ivc melding is possible between the subsystem described ~ ;vu ,l~ and the type of focal reducing relay shown in Fig. 4. The concentric meniscus 44 provides correction of the spherical aberration of the concave spherical mirror; --l- ~ ly of field angle ir~ the same manner as described previously for the basic inventions 30 ,ul~y wo 95/34013 21 Q 2 3 2 8 ; r~
The doublet 45 is afocal and mtroduces a chromatic error equal and opposite to the chromatic error of the meniscus 44. Bemg located at the aperturestop, doublet 45 acts equally on all ray bundles so does not disturb the overall ~ y of the system.
It should be noted that there are two physical centres of curvature in Fig. 4.
The centre of the aperture stop 45 is the centre of curvature of the meniscus 44, but tbis centre is reflected to the position 40 by the folding flat 46. This r -~ makes it possible to achieve an external focus for greater ~C~ y, Field curvature is inherent in concentric designs, as is well known in Schmidt cameras especially, and can be corrected by the insertion of a field flatterling lens 48 close to the focal surface, but, at least in the usual Schmidt ~. ~ " . ~ , only at the expense of Ulll. ' g c~ off-axis .? ",,, ~ ;"
However, as the numerical aperture (the speed) is increased, tbis problem is at 15 least partially offset by the smaller scale of the focal surface geometry. In the cl.lbc ' described in t~?is ~rçrifj~ the field flatterling lenses are so weak as to add no ~ ;..- to the residua~ sphero-chromatic blur.
By merging the aperture stop of the relay and the ll~.~f~ aperture stop of the new subsystem, the fast imaging system is ' ' ~
Figure 5 shows the layout resulting from the merge with ' ' rays shown at a typical off-axis angle in this example at 1.83 degrees offaxis. The system has a primary mirror 51 and a secondary mirror 52. The system also mcludes a corrector group 54 and 55 (the ~ l v ' of meniscus 44 and doublet 45 in Fig 4) and a folding flat 56.
Also visible m Figure 5 is the small weak field flattener 58 wllich delineates the final f~at focal surface. In this particular design, the field flattener lens 58 is intended to be optically cemented to the otherwise .~,..,d silicon - structure of the CCD detector. This minimises additional ~l~tir~nc c,by the field flattener 58 and serves to protect the CCD surface from 30 c Separation of this lens from the focal surface would cause it to intrude too far into the f/l ray cone with implicit degradation of the image sharpness.
As shown in the system in Figure 5, the ~ r `~ C of this system can be ' as:
(a) the focal power resides in the mirrors~ and so is non-chromatic.
(b) the spherical mirrors are optically c, thus ~ ;..,o. coma amd ~ when the aperture stop is located at the centre of curvature (or at the optical equivalent).
(c) spherical aberration correction is the only remaining necessary 10 adjunct to the reflective optical elements. This is the function of the corrector group.
(d) the residual a~h are 1.,.. ~rlih..iP C~ ti~mc of secondary colour with weak higb-order coma and r-'i,., ' , generated primarily at the non-concentric surfaces of the transfer lens.
(e) vignetting is minimal. The central obsc~ht~r~ is ,l. ~. . .- -~;1 by the pprfr~h~nc in the folding and relay mirrors, provided that the design is adjusted so as to image the seconda~y n~irror mto the space between them. In Example I
below, tbe central ~ ,.,. is about 31.2% on axis, increasing to 33% at the ~ill r ~ e ofthe llmmdiameterimage.
(f) distortion is rninimal, witb an amplitude generally less than that of the blur spot ' To min~mise future r~ costs, the example designs make use of "Smith's List" of workshop tool radii for the radii of curvature of the optical Although non-optimum for residual aberration - - - . the 25 difference in ~.. r.. - .~-e is ~ecligible.
The tbree following examples d--- very different variants of the basic design, a 200mm aperture f/0.9 visible/NlR, a lOOOmm aperture f/0.8 visible/NIR amd a 200mm aperture f/0.93 thermal infrared version.
The cl.~ .; r;- ~ ;.... tables are based on a coordinate system in which the z-30 axis is the optical axis and the x and y-axes are mutually Ul ILOC~ to it. Inthese design examples the origin is tbe centre of curvature of the primary rnirror.
W0 95/34013 ~ l a ~ 3 2 ~ r~
_9_ "Diarn" and "diam" are the outside and inside diameters of annuli. The shape of the aspheric trimmer profile is defined by the polyllvll.ial equation: z = c.x2/2 +
a2.x~ + a6.x6 + a8.x8 where c is the curvature, x is the x-coordinate arld a~ are the coPffi -The bandpass for the first two of the examples given for this class of the system is intended to match the spectral sensitivity of generic silicon CCD
devices, for which the highest response lies between 450 and l lOOnm. The Cull~_r ' V refractive index data for optical glass is published for the spec~allines g, e, d, C, r, s and nl060 0 amongst others, providing a good coverage for10 analytic purposes.
The initial ray-tracing process always shows some coma as the dominant residual P~P~rP~inn for off-axis rays, emanating from the non-concentric c, , This is largely corrected by illL-. ' v equal and opposite coma within the concentric ('~Ccp~ subsystem, the technique chosen here being that 15 of increasing the focal length of the transfer lens so as to make the tr~msfer illll.~,lrt;.,lly cu -. rhe effect of this procedure is to displace the centre of the entrance pupil away from the classical Schmidt location (at the centre of curvature of the primaly mirror), and laterally ,UIU~Ol ' to off-axis angle, thus effecting the required c~ Ray tracing is perfoImed thereafter by 20 ensuring that the aperture stop, located at the aspheric surface, accurately delineates the marginal rays for each spectral line.
The median ray aberration graphs which follow, have as their vertical axis the height of the ray in the entrance pupil and the horizontal axis gives the lateral position of the intercept with the focal plane.
The 2D l,;~ are ~ d in , ' ', any ';v~ fine structure is derived from the line-spectrum ray trace. The most relevant feature is the maximum extent of the "ru~l~lilli" on the 32 Y 32~1m focal patch.
Wo95134013 21g~8 ~ ~5~
Surface Glass Z(verte~) Cur~ature Radius Surface Type diam Diam 0 618 Obstruction 95 5 1 1016 -0.00098425 -1016 ~irror 8S 25S
2 633.5 -0.00157853 -633.5 ~irror 92 3 830 0.0046904 213.2 ens 55 4 SK 11 848 -0.00~2549 -190.3 _ens 55 1009.45 0.01619433 61.75 ens 60 10 6 SK 4 iO29.27 O.OZ384927 41.93 ens 60 7 1065 0 fla~ ens 56.5 8 F 4 1071 -0.0072275 -138.4 .ens 56.5 9 SK4 1075 0 lla~+asph .ens(S~op) 56.5 1143.6 0 fla~ dirror 47 105 15 11 1065 0.00679348 147.2 ~irror 60 150 12 1163.67 0.03298915 30.31 ens 12 13 SF2 1164.67 0 flat ocus IZ
Aspheric CoefficieDts of Surface 9 Entrance Pupil ~iam. = 200m A2 -5.50E-05 Focal Length = 173.Zmm 20 A4 1.281E-07 Geometrical Focal Ratio = 0.87 A6 -5.878E-II CeDtral obscura~ioD = 31.2%
A8 -2.184E-14 BaDdDass = 436Dm ~o 1060Dm The profile of the aspheric zonal corrector surface is illustrated in Fig. 6.
25 Note that the z-axis is expanded by a factor of 2000 relative to the (vertical) x-axis. Fig. 7 provides a side elevation of this example design, Fig. 8 gives a graphical ilillc~r?~inn of the computed F ~ ' The ' ' ray aberration curves in Figure 8, d~ moderate stability, with no tendency to chaotic extremes as the field angle is increased. As 30 the 2D l~ show, all the ene}gy from 436 to 1060nm is focused into only part of ~e 32 X 32,um focal area even at 1.4SS off axis (the angular radius CUII~,a~lld;~g to the side of the 7 X 9mm - or "2~ inch" video-standard image).
WO95/34013 21~232~ P-ll L s~
Surface Glass Zlvertex) Curvature Radius Surface Type diam Diam o 3550 Obstruction 250 6000 -0.0001667 -6000 Mirror 1045 5 2 3575 -0.0002797 -3575 Mirror 250 3 4401 0.0065004 144.9 Lens 62 4 F 4 4407 0.0187758 53.26 Lens 62 5 SK 4 4419 -0.0004764 -2099 Lens 62 6 4580.5 0.01619433 61.75 Lens 58 10 7 SK 4 4602.25 0.025 40 Lens 58 8 4636 0 flat Lens 55 9 F 4 4642.25 -0.0085063 -117.6 Lens 55 10 SK 4 4646 0 flat l asph Lens(Stop) 54.6 11 4793.2 -0.0067935 -147.2 Mirror 155 15 12 4693.241 -0.03365497 -27.36 Lens 14 13 SF 2 4692.241 0 flat focus 14 Aspheric ~ '~ of Surface 10 Entrance Pupil Diam. = 1000rnm A2 = -9.6E-05 Focal Len~th = 814.8mm A4 = 2.206E-07 Geometrical Focal Ratio = 0.82 20 A6 = -9.976E-11 Entral Obscuration = 6.3%
A8 = -3.1 59E-14 Bandpass ~ 436nm to 1 060nm At EPDs i" ~ 'y greater than lm, - on the new design systcm are imposed by the greater scale of spherical aberration at the c-25 (~5~CC~ in focus, which gencrates ~ r errors of mapping of the idealentrance pupil onto the system aperture stop by the transfer lens. The resulting high-order ~ -- tend to exceed 9~C~ ' levels relative to the pixel .1: ,. . i ...~ of the d~l~. CCD detectors.
Example 2 describes a lOOOmm aperture version. There is an extra 30 chromatic correction element used in the transfer lens of the lm variant. This helps to tr.im back the outer parts of the blur spot which are caused by the extremes of the spectral bandpass.
Figure 9 shows the side view of the optical layout and Figure 10 gives a graphic illl-cfra~ion of the computer median ray and blur spot ~, c( WO95/34013 ~1~2~28 ~..~sc~- l T~RMAT. INFRARl~D VARIANT
It is clear that other regions of tbe spect~um can be utilised, given the ~)~JIUI ' detectors and refractive media to which this design principle can beadapted. In recent years, arrays of thermal infrared detectors have been 5 fabricated, tbe most useful in the context of the new imaging system being ~e Pt:Pt-Si CCD arriys that are now ~ lly available. With useful spectral sensitivity in the spectral domain 3.5 - 5.5~m, these detectors have overall andpixel ,~ ".~ similar to those of the normal visible/~lR silicon irnagers.
Moreover, in the 3.5 - 5.5~m spectral domain, ~e is a low-cost, 10 easily worked optical medium suited to the refractive ~ . . of the fast relay, with the benefit that the high refractive index allows large .~ in the spherical curvatures of the field/transfer lens giving a c~ l,lhlg ~ r;~
reduction of the high-order ~ .. ".l ;....~ which limit the off-axis p.. r... ~ ., - e of the visible/NIR version of this design.
wo 9S/34013 21~ 2 3 2 8 F~
Surf ce Gl-~ Z(verte2~) Curv~ture RldiU~ Smf ceType di-m Di-m - o 620 Obstruction 88 1000 -0.002 -1000 ~or 80 260 5 2 62s -0.0016 -625 ~ror 88 3 836.31 0.001523 6s6.6 Lens s4 4 Ge 846.31 o flnt Lens s4 s 1082.11 0.01727414 s7.ss Lens 70 6 Ge 1089.35 0.01974334 5065 Lerls 70 10 7 1135 0.00021 4761.9 Lens 70 8 AL2o, 1140 o flat+asph Lens (stop) 70 9 1232.5 o flat M~r s3 125 o 1125 o.oos 200 Mirror 7s 180 Il 1244.13 0.01236553 80.87 Lens 33 15 12 Ge 1248.41 0.0130s6s4 76.ss Lens 33 .374 0.024s7032 46.36 Lens 12 o~ 1261.374 o ~dat iOCUs 12 ~-pheric coemdent~ o~ Surf~ce g Erltra~ce Pupil Diam. = 1 s6mm A2 -I . ~4E-05 Focal Le~lg h = 181 .2mm A4 5 . 1 9E-08 Geometrical Foc21 F~ho = 0.93 A6 -I .03E-1 I Central obscuration = 29%
A8 -g.OOE- I s sandpass = 3.7 - 5.5L m The table of Example 3 lists the optical desigil of a thermal version of the 25 new system, . . ' I - in most . ~ to those of the example given in Table 1. Figure 11 shows the side view of t~te optical layout.
The ~;~ .. I; ~ Lff~ m detail mclude the use at the aper~ure stop of a syntbetic sapphire spectial dispersion corrector I IS which has only a singlet format, but which has a weak positive power exactly sufficient for the ~
30 positive 1 ~ ' I c~tromatic aberration to correct the negative chromatic aberration of the ~. concentiic meniscus corrector over the spectral band 3.7 - 5.5,um.
WO95134013 2~g2328 r~".,~
An essential c, , of a thermal camera of this type is the cryostat sub-system. The cryostat wirldow is usually made as arl optical flat, but with the fast optics in this design, it is more ~ , to fabricate the window as a concentric meniscus 119 with its centre of curvature coincident with the 5 re~ectiorl of the common centre of culvature created by the folding flat. A
pvlayvvLvr view is shown in Fig. 12. This window then ' to tbe corrective negative spherical aberration of the system and introduces no off-axis 9~
Figure 13 illustrates the computed ~ of the mediarl ray bundles 10 and of the blur spot.
A possible advantage of at least preferred forms of the present invention over prior art designs such as provided by the Hawkins and Linfoot camera as thebasis for the design of the focal reducmg relay, is that the corrector meniscus is truly c : v, and the chromatic doublet has zero power, thus giving more 15 degrees of freedom to the designer. The classical Maksutov corrector is designed a~ ;L~ non-cr~nc~1Tir~ so asto lly . , forits chromatic aberration for small angles off axis; however, it is believed that at least preferred forrns of the present invention exceed allowable off-axis arlgles irl this case.The extra degrees of freedor~ ~ above can be used to 20 a~Oclu~ the system, in that optical glasses can be selected for the meniscus and the chroma~ic doublet which permit a sharp focus for more than the usual two ~a~ implicit in the usual - ', - correction.
~ perifir~lly, by choosing Schott FK 51 for the meniscus, the chrornatic aberration to be corrected by the doublet is !~ to the extent that the 25 glasses KzF N2 and PK 5 la can be utilised to provide a~cLl over the bandpass 400 to 1 lOOnm (the entire sensitive bandpass of typical silicon-based CCD imaging devices), while retaining the zero-power qleri~rs*~ of the doublet. A triplet form allows even further gains in aberration control.
The result of this is that the resolution of the system is improved by a factor 30 of a~ y 3, with blur-spot ~ potentially as low as 5 llf~ lvh~va over the entire image area, at speeds of the order of flO.8 and for the 2~92328 WO 95134013 r~ ,s.C~~~
bandpass ~ n~in-~d above. This, in turn, implies the ability to scale up tbe design so as to q~cn~ ' the newer very large silicon CCD imaging devices now coming into use in .~tl~ ' and other scientific research.
SCALING
All three examples given here are based on the use of a "Z~mch" video standard CCD detector, which effectively ~ the linear ~' of the fast relay sub-system for a specified Numerical Aperture. Other detector may require ",~ ;.... of the relay to provide the a~ U~ ' ' of speed, linear field at the fieldlt~ansfer lens, and residual 10 aberration blur.
From the three examples it can be seen how, once the d~,t~.lul/ll,l~
cnnlh;-qtinn has been initially ~ ~, the Cqecpgr~qin can then be ~ which will match the required object field a~gle to the linear field of the relay. Melding of the two sub-systems is then achieved by detailed 15 q~lq,rtqti~n of the fieldltrnsfer and corrector
Claims (21)
1. A lens system suitable for focusmg substantially parallel incident light ontoa detector, said system comprising (A) a concentric spherical Cassegrain-like system of two mirrors, (B) a concentric spherical focal reducer, (C) a transfer lens system which combines the concentricity of the Cassegrain-like system of two mirrors and of the concentric spherical focal reducer by imaging the first centre of concentricity (that of the system of two mirrors) on the second centre of concentricity (that of the focal reducer) to thereby provide a single optically concentric system which combines their advantages, (D) means to correct the sum of the spherical aberration of all of the spherical mirrors m the entire system, and (E) an aperture stop.
2. A lens system as claimed in claim 1 further including:
(F) image detection means (hereafter "detector") at the focus of the focal reducer.
(F) image detection means (hereafter "detector") at the focus of the focal reducer.
3. A lens system of claim 1 or 2 wherein said concentric spherical Cassegrain-like system of two mirrors does not include any aperture stop.
4. A lens system of claim 1, 2 or 3 wherein said concentric spherical focal reducer includes at least one spherical mirror element.
5. A lens system as claimed in claim 1, 2 or 3 wherein said concentric spherical focal reducer includes at least one refractive element.
6. A lens system as claimed in an one of claims 1 to 4 wherein said transfer lens system is a refractive single lens.
7. A lens system as claimed in any one of claims 1 to 5 wherein said concentric spherical focal reducer is selected from the group comprising i. Modified forms of Baker camera;
ii. Modified form of Hawkins and Linfoot camera;
iii. Derivation of Maksutov or Bouwers camera.
ii. Modified form of Hawkins and Linfoot camera;
iii. Derivation of Maksutov or Bouwers camera.
8. A lens system as claimed in any one of claims 1 to 6 wherein said concentric spherical focal reducer is a modified form of the Hawkins and Linfootcamera system and said meams to correct the sum of the spherical aberration of all of the sphericai mirrors in the entire system and said aperture stop forms part thereof.
9. A lens system as claimed in any one of claims 1 to 7 wherein said means to correct the sum of this spherical aberration of all of the spherical mirrors in the entire system is a concentric meniscus concentric with the concentric focal reducer.
10. A lens system as claimed in any one of claims 1 to 7 wherein the chromatic aberration introduced by the said concentric meniscus is compensated by a refractive component located at the aperture stop.
11. A lens system as claimed in claim 9 wherem said refractive component is a zero-power chromatic doublet lens.
12. A lens system as claimed in claim 9 wherein said refractive component is a weakly positive power singlet lens.
13. A lens system as claimed in claim 9 wherein said refractive component includes an aspheric zonal corrector surface sufficiently weak not to introduce any substantial degree of focal difficulties when instant light is angled into the overall lens system other than axially.
14. A lens system as claimed in any one of claims 1 to 12 faster than f/1.
15. A lens system as claimed in any one of claims 1 to 13 wherein said system is about f/0.8.
16. A lens system as claimed in any one of claims 1 to 14 wherein said detector is included.
17. A lens system as claimed in amy one of claims 1 to 15 wherein said detector is a solid state detector.
18. A lens system as claimed in any one of claims 1 to 16 wherein said detector has a substantially planar detection surface.
19. A method of imaging onto am imaging detector substantially parallel incident light said method comprising the steps of (i) creating an intermediate image with a concentric spherical Cassegrain-like system of two mirrors with an entrance pupil located at the centre of curvature of the mirror, and (ii) relaying the intermediate image to the imaging detector by a concentric spherical fast focal reducer the method being chatacterised in that (A) a refractive transfer lens or lens system located at or near the intermediate image serves the following functions (a) as a field lens for the intermediate image, (b) as a meams to link the independent concentricities of the concentric spherical Cassegrain like system and the concentric spherical fast focal reducer, and (c) as a means to define an aperture stop being the image of the entrance pupil, and (B) a concentric meniscus corrector is provided in the fast focal reducer to correct the spherical aberration of the whole system.
20. A method of claim 19 wherein the relative sizes of the entrance pupil amd the aperture stop match the detector characteristics to the task of the system.
21. A method of claim 19 wherein the size of the aperture stop can be chosen to be much smaller than that of the entrance pupil, enabling high values of Numerical Aperture amd an exceptional degree of aberration correction, thus permitting an optimum matching of the detector characteristics to the task of the system.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NZ26069694 | 1994-06-07 | ||
| NZ260696 | 1994-06-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2192328A1 true CA2192328A1 (en) | 1995-12-14 |
Family
ID=19924810
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2192328 Abandoned CA2192328A1 (en) | 1994-06-07 | 1995-06-07 | High speed optical system |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0770224A4 (en) |
| JP (1) | JPH10505432A (en) |
| CA (1) | CA2192328A1 (en) |
| WO (1) | WO1995034013A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2001512853A (en) * | 1997-08-12 | 2001-08-28 | インダストリアル リサーチ リミテッド | Camera with image reduction relay system |
| AU9369398A (en) * | 1997-10-20 | 1999-05-10 | Industrial Research Limited | An improved surveillance system |
| WO2002093231A1 (en) * | 2001-05-15 | 2002-11-21 | Industrial Research Limited | Optical imaging system with aberration correcting means |
| ITNA20090061A1 (en) * | 2009-10-05 | 2011-04-06 | Optimath Srl | NEW OPTICAL COMBINATION FOR TELESCOPES WITHOUT THE LIMITATION OF THE DIAMETER DUE TO THE CORRECTOR SIZE. |
| CZ307952B6 (en) * | 2015-03-25 | 2019-09-11 | Univerzita Palackého v Olomouci | Refractive afocal optical system for correcting colour defects of diffractive imaging elements |
| WO2016201604A1 (en) * | 2015-06-15 | 2016-12-22 | 中国航空工业集团公司洛阳电光设备研究所 | Imaging device |
| CN109324403B (en) * | 2018-09-28 | 2020-05-19 | 中国科学院长春光学精密机械与物理研究所 | A Large Aperture and Long Focal Length Imaging Optical System for Splicing Mirror Experiments |
| CN113766218B (en) * | 2021-09-14 | 2024-05-14 | 北京集创北方科技股份有限公司 | Position detection method of optical lens, electronic device and storage medium |
Family Cites Families (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3711184A (en) * | 1971-04-12 | 1973-01-16 | Kollsman Instr Corp | Large catadioptric objective |
| US4043643A (en) * | 1976-05-14 | 1977-08-23 | Kms Fusion, Inc. | Catadioptic telescope |
| US4101195A (en) * | 1977-07-29 | 1978-07-18 | Nasa | Anastigmatic three-mirror telescope |
| US4240702A (en) * | 1978-09-08 | 1980-12-23 | The Perkin-Elmer Corporation | Field corrector for two mirror objective systems |
| JPS55109959A (en) * | 1979-02-16 | 1980-08-23 | Hitachi Ltd | Sodium ionization detector electrode |
| US4342503A (en) * | 1979-10-09 | 1982-08-03 | The Perkin-Elmer Corporation | Catadioptric telescopes |
| DE3121044A1 (en) * | 1981-03-19 | 1982-09-30 | Erwin Dr Ing Wiedemann | Catadioptric lens of high speed |
| JPS58210234A (en) * | 1982-05-31 | 1983-12-07 | 松下電工株式会社 | Building material |
| GB2136149B (en) * | 1983-03-03 | 1986-02-12 | Barr & Stroud Ltd | High magnification afocal infrared telescopes |
| JPS6160772A (en) * | 1984-08-31 | 1986-03-28 | Sunstar Giken Kk | Method for processing metallic panel |
| US4624538A (en) * | 1985-05-28 | 1986-11-25 | The Perkin-Elmer Corporation | Coma-compensation telescope |
| JPS63242635A (en) * | 1987-03-31 | 1988-10-07 | 日新製鋼株式会社 | Vibration-damping metallic plate |
| SU1689910A1 (en) * | 1989-10-02 | 1991-11-07 | Красноярский государственный университет | Mirror objective |
| US5089910A (en) * | 1990-06-28 | 1992-02-18 | Lookheed Missiles & Space Company, Inc. | Infrared catadioptric zoom relay telescope with an asperic primary mirror |
| JPH0682699A (en) * | 1991-06-03 | 1994-03-25 | Her Majesty The Queen In Right Of New Zealand | Lens system |
| JPH05495A (en) * | 1991-06-24 | 1993-01-08 | Kobe Steel Ltd | Method for processing composite metal sheet |
| DE4301291C2 (en) * | 1993-01-15 | 1999-08-19 | Gallert | Universal double mirror corrector for Cassegrain and Ritchey Chretien mirror systems |
| DE4322536A1 (en) * | 1993-07-02 | 1995-01-12 | Frank Gallert | Aplanatic and anastigmatic mirror system with a plane image field |
-
1995
- 1995-06-07 EP EP95922012A patent/EP0770224A4/en not_active Withdrawn
- 1995-06-07 WO PCT/NZ1995/000051 patent/WO1995034013A1/en not_active Application Discontinuation
- 1995-06-07 CA CA 2192328 patent/CA2192328A1/en not_active Abandoned
- 1995-06-07 JP JP8500709A patent/JPH10505432A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| JPH10505432A (en) | 1998-05-26 |
| EP0770224A4 (en) | 1998-11-25 |
| WO1995034013A1 (en) | 1995-12-14 |
| EP0770224A1 (en) | 1997-05-02 |
| AU686393B2 (en) | 1998-02-05 |
| AU2684795A (en) | 1996-01-04 |
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| EEER | Examination request | ||
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