T3D Re: Distortion et al in zooms! (TECH-3D digest 283)

["Bob Howard" <bobh@xxxxxxxxxxxxxxxxxx>]

RE: worries about distortion (I supposed wondering if stereo images 
will match??) in zooms. I doubt if any zooms are 1% over the range as 
John B. suggests. I doubt if normal 50mm lenses can do this!! As all 
SLR ones are retrofocus. Keppler in a recent column of Pop Photo 
questioned if modern lenses had to be retrofocus because of the 
mirror clearance, citing that he knew of 50mm and less Exakta lenses 
pre-war (WW2). But he forgot that not being prism reflexes they used 
short mirrors. With the prism came the need for brightness and full 
sized mirrors that limited focal length to 52mm or longer untill the 
retrofocus allowed 50mm and wide angles to be made. (Retrofocus is 
Angineaux trademark that became generic to describe long backfocus 
lenses that were farther from the film than the focal length.)
These lenses and most not design for aerial photograph or copying 
sacrifice distortion as usually not noticed except with windows and 
doorways near edge of frame.
A worse revelation was that internal focusing zooms cheat on focal 
length as they focus as marked focal length is only for infinity to 
meet trade standards. Pop photo found this out when comparing zooms 
and noticing image size differences. So I would suggest that zooms 
suck in stereo. BobH


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