Re: XA Lenses [photo-3d] Digest Number 149

[robhoward@xxxxxxxxxxx]

RE: Reverse Retrofocus lenses on XA!
     Mike (I think?) was right in saying a telephoto lens had a shorter 
lens to film distance that its marked and effective focal length.
However, a Retrofocus (originally a Angineaux trademark) lens, as 
first made for early prism SLRs in 35mm, e.g. Exakta, was a wide 
angle 35mm! It had a long backfocus since the mirror in SLRs 
swung through an arc that  limited a lens to near 55mm. (Later cutoff 
mirrors shortened this to perhaps 40mm. So no wideangle lenses 
for 35mm SLRS until the Angineaux lens. (Taylor Hobson and 
Cooke had developed similar lens for multifilm Techicolor camera).
The Reverse Retrofocus lens on the XA is a 35mm lens with a 
backfocus LESS than 35mm! This was new and made body and 
lens very compact. The later f/3.5 version was not a cheapie but 
improved on the f/2.8 in some optical respects.
Moxom is confusing the fact that telephoto lenses are common 
(compared to long focus..lens distance = focal length.),With the 
need for all SLR lenses of less than about 55mm to be retrofocus 
to clear SLR mirror.  That's why there were no 50mm lenses at first, 
most being 55mm or 58mm in 35mm SLRs.    Bob Howard
Bob Howard (robhoward@xxxxxxxxxxx)
also: bobh626@xxxxxxxxxxx