Wide angle for A7/R?

Started Feb 26, 2014 | Discussions thread
Godfrey Forum Pro • Posts: 29,359
Re: Wide angle for A7/R?

Mel Snyder wrote:

Hey, let's not make blanket statements like "most M-mount RF lenses should be used on a camera designed to work with them specifically."

Why not? It's just my opinion.

As long as distance between the lens mount and the sensor are correct, I'm not sure the sensor knows whether the lens is from a rangefinder or an SLR.

The problem is the long-discussed issue which is the most important difference between a sensor and film when it comes to lens compatibility and performance. Film is insensitive to the incident angle of the light hitting it, imager sensors happen to be very sensitive to that. Digital sensors perform best when the light from the lens strikes them dead one, orthogonal to the plane of the sensor. So if a lens design has a ray-trace which deviates more than a certain amount off the orthogonal, quality suffers.

It is far more likely that SLR lenses will be compatible on this criteria due to the fact that all SLR lenses have been designed to be far enough from the image plane to clear the moving mirror.

My 1981 35mm f1.4 Summilux M performs on my A7 with precisely the same strengths and weakness it does on my M4P (charitably termed "dreamy" wide open, sharp as a tack across the frame by f2.8-4); my 1982 50mm f2 Summicron M and 90mm f2.8 Tele-Elmarit perform even better on digital sensors than they did on film.

I'm glad you're getting such good behavior out of your Summilux 35mm, Summicron 50, and Tele-Elmarit 90. Not everyone is having such luck, particularly with the 35mm focal length. Some work well, others do not. There are some surprises too. Seems the Nokton 35mm f/1.2 is another winner.

I have ten M-mount lenses, ranging from 21 to 135mm. After testing them all with the A7, the two 40mm lenses (Nokton 40/1.4 and M-Rokkor 40/2—same lens design as the Summicron-C 40/2), the M-Rokkor 90/4 (same as the Elmar-C 90/4) and Hektor 135/4.5 are the only ones that work satisfactorily for me. The Color Skopar 21, 28, and 35, the Ultron 28/2, and (surprisingly) the Nokton 50/1.5 ASPH (LTM) are simply too compromised to be worth bothering with. I haven't tested the Color Skopar 50/2.5 yet, but it's semi-permanently fitted to my M4-2 so I probably won't bother.

I agree on rangefinder wide angles - I can't imagine why there is such a desire to shoot wide angle rangefinder lenses on A7/r cameras, anyway. At their pinnacle back in the 1980s, they were optically challenged, to put it mildly, useful for journalism, not landscapes or cityscapes. But let's not lump those lenses with longer focal lengths, which perform brilliantly on the A7.

I don't know about that. My '80s Elmarit-M 21 and 24 mm lenses performed pretty darn nicely on film. The reports I've heard from others using them are poor. I do agree that in general the longer lenses work ok, but then they should ... the Nokton 50 is surprisingly that it works so poorly. And then there's also the fact that all RF lenses have relatively limited close-focus capabilities compared to SLR lenses.

Meanwhile, I just did a quick-test of the Nikkor 18mm f/3.5 AI-S. No smearing at corners even wide open, sharp as a tack by f/5.6-f/8, no color shifting at all. 100 degrees FoV across the diagonal. Now that's a decent match.

For me, I put RF lenses on RF cameras. The A7 is much more like working with an SLR anyway with its beautiful TTL focusing and precise framing capabilities.

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