A little bit about the
Pentax LX focusing screens



Type Length f SC-21 SC-26 SA-21 SA-23 SA-26 SB-21 SD-21 SD-11 SE-20 SE-25 SG-20 SI-20
Fisheye 17mmf4 ×   ×     ×            
Normal


To


Telephoto		 15mmf3.5 ×   ×     ×            
18mmf3.5 ×   ×     ×            
20mmf4 ×   ×     ×            
24mmf2.8 ×   × ×   ×            
28mmf2 ×   × *   ×            
28mmf2.8 ×   × ×   ×            
30mmf2.8 ×   × ×   ×            
35mmf1.4 ×   × *   ×       ×    
35mmf2 ×   × *   ×            
35mmf2.8 ×   × ×   ×            
40mmf2.8 ×   × ×   ×            
50mm1.2 ×   × *   ×       ×    
50mmf1.4 ×   × *   ×       ×    
50mmf1.7 ×   × ×   ×       ×    
50mmf2 ×   × ×   ×            
85mmf2 × × × × × ×       ×    
100mmf2.8 × × × × × ×       ×    
120mmf2.8 × × × × × ×       ×    
135mmf2.5 × × × × × ×       ×    
135mmf3.5 × × ×   × ×       ×    
150mmf3.5 × × ×   × ×       ×    
200mmf2.5 × × × × × ×       ×    
200mmf4 × × ×   × ×       ×    
300mmf4 × * ×   * ×       *    
400mmf5.6   *     *       × * × ×
500mmf4.5 × * ×   * ×     × *    
1000mmf8   *     *       × * × ×
Reflex 1000mmf11                 × * × ×
2000mmf13.5                 × * × ×
Zoom


Lenses		 24->35mmf3.5 ×   ×     ×     ×      
24->50mmf4 ×   ×     ×            
28->50mmf3.5->f4.5 ×   ×     ×            
35->70mmf2.8->f3.5 ×   ×     ×            
40->80mmf2.8->f4 ×   ×     ×            
45->125mmf4 × × ×   × ×       ×    
75->150mmf4 × × ×   × ×     × ×    
80->200mmf4.5 × × ×   × ×     × ×    
135->600mmf6.7   ×     ×         ×    
Macro 50mmf4 ×   ×     ×            
100mmf4 × × ×   × ×       ×    
Bellows 100mmf4 × × ×   × ×       ×    
Shift 28mmf3.5 ×   ×     ×     ×   *  
for Photomicrography, Astrophotography,
Medical Photography and Macro Lenses		           × *        
SD-21 Useful for close-ups with other lenses at apertures of f4.5 or smaller ^ ^
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SD-11 Useful for close-ups with other lenses at apertures of f4.5 or smaller
SE-20 Useful for close-ups with other lenses at apertures of f4.5 or smaller
SG-20 Useful with other lenses when seeking to determine the size of a subject
SI-20 Useful with other lenses when seeking to determine the size of a subject in millimeters
Do not use the SA-23, SC-26, SA-26, and SE-25 screens with a rear (tele) converter K-T6-2X mounted on the lens.