Patent Publication Number: US-4482219-A

Title: High speed catadioptric objective lens system

Description:
This is a continuation, of application Ser. No. 967,973 filed Dec. 8, 1978, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an improved reflecting-refracting high speed objective lens in which all optical elements are assembled in two members. 
     2. Description of the Prior Art 
     The reflecting objective lens, as initially used in astronomy, is distinguished by its ideally achromatic image which is exceptionally useful with large focal lengths. A further advantage over refracting lenses is given by the reduced length which enhanced the use of reflecting telephoto lenses in photography. 
     Recently reflecting lenses have proven very useful for electronic infrared- and night-vision systems featuring high speed--high contrast objectives with reduced image angle. Reflecting-refracting or catadioptric lenses were designed in order to use only spherical mirrors, to extend the field of view and to reduce image errors by introducing ordinary refracting lenses for correction purposes. The thus created Maksutov-lens nevertheless exhibits a large zonal error of spherical aberration. 
     Another similar type, the Mandler-lens, having a two member front part (it likewise presents a large zonal error of spheric aberration) is disclosed e.g. in F. I. Havlicek, L. Canzek &#34;Zum Korrigieren von Spiegelobjektiven&#34;, Deutsche Geodatische Kommission bei der Bayerischen Akademie der Wissenschaften, Reihe A, Heft 42, Munchen 1963. 
     A further improvement was brought about by using a one member front lens, the silvered central part of which constitutes the second mirror, while the first or main mirror has a central bore as disclosed by Swiss Pat. No. 542,454. These known objective lenses nevertheless suffer from at least one of the following short-comings: 
     (a) A central bore is applied to the main mirror involving a high cost, machining of a ring-shaped lens is difficult, and such a lens has a reduced mechanical stability as compared to a solid lens. 
     (b) The front lens, the main mirror and the field lens system are rather sensitive to centering. Without exact centering troublesome comatic and astigmatic defects are unavoidable. 
     (c) Mounting of the field lenses within the objective requires a first precise mount, another mount is necessary for securing the field lens system within the objective housing. This multi-mounting method involves centering errors which in turn cause coma and astigmatism. 
     SUMMARY OF THE PRESENT INVENTION 
     The principal object of this invention is to provide a high speed compact catadioptric objective system of simple construction and high image quality with improved performance with respect to the above mentioned deficiencies. 
     The optical system of this invention comprises, in accordance with the advance of the light rays, a positive lens with a convex surface toward the object, a solid lens with front and back surface concave toward the object and with a main mirror lens constituted by the peripheral portion of said solid lens, a counter-mirror surfaced to the central portion of said positive lens and a field lens cemented to the central portion of said lens with the main mirror surfaced on the peripheral portion thereof. This catadioptric system comprises only two optical members which carry said mirrors and of which at least one member carries an additional lens element. 
     The present invention will be described more in detail with reference to illustrative embodiments shown in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a cross section of a first embodiment of the present invention; 
     FIG. 2 shows a cross sectional view of a further embodiment of this invention; 
     FIG. 3 shows a cross section of a third embodiment of this invention; 
     FIG. 4 illustrates a cross section of another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments shown in FIGS. 1 through 4 have only two optical members. As disclosed in FIG. 1 and FIG. 2 a front lens L 1  is surfaced with a counter-mirror M 2  on the central portion of its back surface facing the image side of the lens system. A main mirror lens M 1  is constituted by the outer portion of a solid lens L 4 , the reflecting back surface of which faces the image side. This lens L 4  has no center bore and a field lens L 2  as shown in FIG. 1 or L 2 , L 3  as shown in FIG. 2 is cemented to the central portion of lens L 4  facing the object side. 
     In FIG. 3 is shown a third embodiment of the invention likewise comprising a front lens L 1 , a solid lens L 4  and a field lens L 2  cemented to the central portion of lens L 4 . The counter-mirror M 2  now is surfaced on the central portion of the front surface of the front lens L 1  facing the object side, and an additional lens element L 5  is cemented on the central portion of the back surface of lens L 1  facing the image side. 
     The objective system illustrated in FIG. 4 also includes a front lens L 1 , a solid lens L 4  and a field lens L 2  cemented to the central portion of lens L 4 . A lens element L 5  with the counter mirror M 2  surfaced on its back-object side is cemented to the central portion of the surface of front lens L 1  facing the image side. 
     According to the above described construction a high speed catadioptric objective system lens is obtained, the image quality of which features a very reduced sensitivity to centering errors. The examples shown are highly corrected with respect to spherical and chromatic aberration, coma and astigmatism. They allow a compact construction and render superfluous a separate mechanical mount for the field lens system. An economical production and a reduced sensitivity to machining and mounting errors are brought about by the invention as it employs only two optical members for the objective. 
     The examples 1, 2, 3 and 4 of embodiments described above with reference to FIGS. 1, 2, 3 and 4 are shown in the following tables, where F is the aperture or speed of the lens system, f is the focal length and s&#39; is the back focal distance. 
     EXAMPLE 1 
     
         ______________________________________                                    
F = 1:1.2      Thicknesses                                                
f = 99.7       and                                                        
s&#39; = 8.7       Separations n.sub.d ν.sub.d                             
______________________________________                                    
L.sub.1                                                                   
       r1 = +747.831                                                      
                   d1 = 7.5    1.76180                                    
                                     27.0                                 
       r2 = -2214.349                                                     
                   a2 = 46.9                                              
M.sub.1                                                                   
       r3 = -137.033                                                      
                   d3 = 8      1.68900                                    
                                     49.4                                 
       r4 = -198.791                                                      
                   d4 = d3                                                
       r5 = r3     a5 = a2                                                
M.sub.2                                                                   
       r6 = r2     a6 = 41.9                                              
L.sub.2                                                                   
       r7 = +37.388                                                       
                   d7 = 5      1.46450                                    
                                     65.8                                 
       r8 = r3     d8 = d3                                                
L4     r8 = r3     d8 = d3     1.68900                                    
                                     49.4                                 
       r9 = r4                                                            
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     EXAMPLE 2 
     
         ______________________________________                                    
F = 1:1.2      Thicknesses                                                
f = 99.5       and                                                        
s&#39; = 9.0       Separations n.sub.d ν.sub.d                             
______________________________________                                    
L.sub.1                                                                   
       r1 = +639.795                                                      
                   d1 = 7.5    1.74000                                    
                                     28.2                                 
       r2 = -2444.988                                                     
                   d2 = 47.1                                              
M.sub.1                                                                   
       r3 = -138.122                                                      
                   d3 = 8      1.68900                                    
                                     49.4                                 
       r4 = -201.857                                                      
                   d4 = 18                                                
       r5 = r3     a5 = 12                                                
M.sub.2                                                                   
       r6 = r2     a6 = 89.7                                              
L.sub.3                                                                   
       r7 = +37.94 d7 = 0.5    1.59551                                    
                                     39.2                                 
       r8 = +29.527                                                       
                   d8 = 4.9                                               
L.sub.2                                                                   
       r8 = +29.527                                                       
                   d8 = 4.9    1.46450                                    
                                     65.8                                 
       r9 = r3     d9 = d3                                                
L.sub.4                                                                   
       r9 = r3     d9 = d3     1.68900                                    
                                     49.4                                 
       r10 = r4                                                           
______________________________________                                    
 
    
     EXAMPLE 3 
     
         ______________________________________                                    
F = 1:1.2      Thicknesses                                                
f = 99.4       and                                                        
s&#39; = 7.6       Separations n.sub.d ν.sub.d                             
______________________________________                                    
L.sub.1                                                                   
       r1 = +343.171                                                      
                   d1 = 7.5    1.51454                                    
                                     54.7                                 
       r2 = -590.667                                                      
                   a2 = 53.7                                              
M.sub.1                                                                   
       r3 = -267.451                                                      
                   d3 = 8      1.51680                                    
                                     64.2                                 
       r4 = -420.875                                                      
                   d4 = d3                                                
       r5 = r3     a5 = 48.9                                              
L.sub.5                                                                   
       r6 = +212.359                                                      
                   d6 = 4.8    1.58215                                    
                                     42.1                                 
       r7 = r2     d7 = d1                                                
M.sub.2                                                                   
       r8 = r1     d8 = d1                                                
L.sub.5                                                                   
       r9 = r2     d9 = d6     1.58215                                    
                                     42.1                                 
       r10 = r6    a10 = 40.9                                             
L.sub.2                                                                   
       r11 = +35.652                                                      
                   d11 = 8     1.56883                                    
                                     56.1                                 
       r12 = r3    d12 = d3                                               
L.sub.4                                                                   
       r12 = r3    d12 = d3    1.51680                                    
                                     64.2                                 
       r13 = r4                                                           
______________________________________                                    
 
    
     EXAMPLE 4 
     
         ______________________________________                                    
F = 1:1.2      Thicknesses                                                
f = 99.3       and                                                        
s&#39; = 10.0      Separations n.sub.d ν.sub.d                             
______________________________________                                    
L.sub.1                                                                   
       r1 = +174.38                                                       
                   d1 = 7.5    1.54041                                    
                                     51.1                                 
       r2 = +1165.501                                                     
                   a2 = 46.7                                              
M.sub.1                                                                   
       r3 = -205.617                                                      
                   d3 = 8      1.62004                                    
                                     36.4                                 
       r4 = -280.458                                                      
                   d4 = d3                                                
       r5 = r3     a5 = 42.5                                              
L.sub.5                                                                   
       r6 = +369.399                                                      
                   d6 = 4.3    1.62237                                    
                                     36.0                                 
       r7 = r2     d7 = d6                                                
M.sub.2                                                                   
       r7 = r2     d7 = d6                                                
L.sub.5                                                                   
       r8 = r6     a8 = 32.4   1.62237                                    
                                     36.0                                 
L.sub.2                                                                   
       r9 = +37.489                                                       
                   d9 = d10    1.4650                                     
                                     65.8                                 
       r10 = r3    d10 = d3                                               
L.sub.4                                                                   
       r10 = r3    d10 = d3    1.62004                                    
                                     36.4                                 
       r11 = r4                                                           
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 It will be appreciated that various modifications and changes of the
 preferred embodiments described above may be made without leaving the
 scope of the invention as defined in the accompanying claims.