retrofocus lenses and RFs...

[mooge]

I've heard the claim that non-retrofocus lenses are generally superior to retrofocus ones... but aren't alot of the modern RF wides retrofocus designs?

is there an easy way to tell?

just curious...

 

[former member]

Look through the lens from both ends, the magnification as viewed from each end will be different.

 

[mtargz]

Even though there are quite a few retrofocus RF lenses, they are still easier-to-design-as-well, since not all retrofocus designs are equal: The retrofocus designs of a rangefinder 21mm lens are much less extreme than those required by an SLR 21mm lens.

In the Zeiss range, it's very easy to tell: Distagon is the name for retrofocus wides, Biogon (and in an extreme case, Hologon) are the names for "regular" wides. I also believe the entire Voigtlander range is non-retrofocus: At least, the 12mm, 15mm and 21mm aren't (which makes them so compact).

 

[mooge]

huh. but what about how far the lens extends behind the lens mount? does that have anything to do with the lens being retrofocus or not or does it have to do with just the lens design?

thanks guys.

 

[rogerzilla]

Yes, a retrofocus lens doesn't project (much) behind the lens mount and the light rays are more parallel between the lens and film.

Digital sensors really need retrofocus designs since they aren't good with light coming in at really shallow angles; hence if you use a CV 21mm lens on a Leica M9, it will have terrible falloff and colour fringing which will require a lot of post-processing to correct. Film doesn't really care about the angle the light hits it; you can get brightness falloff at large apertures but that is usually due to mechanical vignetting of some sort.

The original reason for a retrofocus design was to clear an SLR mirror. Retrofocus designs have a nasty tendency to "pull" the image at the edges which a simpler non-retrofocus design doesn't do. If I keep the camera back vertical and level, my CV 21/4 produces images that could have come from a 50mm or 90mm - no distortion or wacky "ultra wide" effects.

 

[kram]

The main reason, I believe, why there are some retrofocus ZM lenses, is so that there is room behind the lens for the TTL metering to work.

 

[Roger Hicks]

Avoids vignetting. Most modern ultra-wides have some degree of retrofocus design. Look at a 21/3.4 Angulon or 21/4 Nikkor (highly symmetrical, small rear element very close to film plane) and more modern designs (bigger glasses, further away).

Cheers,

R.

 

[kbb]

The symmetrical wide angle can have near perfect absence of distortion, and high MTF, etc, but always will suffer increased illumination falloff due the various laws of physics and optics.
The retrofocus-- or to use it's correct name: inverted telephoto--design permits much more even illumination across the frame, but geometric distortion becomes more difficult to correct.
Even Leica bailed on the symmetrical design for the 21mm by 1979--of course , they had a little light meter on a stick swinging in front of the film plane to deal with.