Wide-angle: the Achilles' heel of SLRs?

[David Lyga]

Because of the inability to place the rear element closer to the film plane (the mirror gets in the way) RFs are touted as having superior wide-angle results. We know that this is so in theory and that compromises had (and still have?) to be made with optical formulas in order to 'compensate and correct'.

But, I ask, is this still so, with computer technology determining, most efficiently, the lens formulas of today? In other words, is a top flight Nikon wide angle (say 20, 24, of 28) inferior in any way to a Leica RF lens of the same focal length? - David Lyga

[AgX]

As you indicated hat mirror issue made it neccesary to exchange a classic wide-angle design for a retro-focus design, probably introducing additional abberations.

Nonwithstanding any achievements in retro-focus desings on which you inquire, the retro-focus principle lets the imaging rays fall onto the film with steaper angles than with the classic concept, thus the cosines-law will have less effect. Thus no need for a correcting density filter and by that a virtual speed gain of such lenses.

[illumiquest]

If a 4000$ Leica 21mm isn't better than a 650$ Nikon 20mm...

[David Lyga]

AgX: So, (in my mathematical ignorance) does that mean that the 'steeper angles' forgo the need to worry about the edges being less exposed? In terms of resolution, however, is this retro-focus compromise just as good? (Hope that I made at least some sense!) - David Lyga

[Mark Crabtree]

I thought this would be about the difficulty focusing wide angles on slrs. That is the Achilles' heel of slrs to me, and also the place rangefinders really shine.

For the rest, I'm in agreement with AgX that the retrofocus design can offer some advantages. Still, there are trade offs. The best modern slr wide angles are supposedly fabulous, but are generally much larger than I would want. Rangefinder lenses are usually a much smaller package.

BTW, many rangefinder lenses shorter than 35 are retrofocus too, but still shorter than slrs. Leica started doing that in the 70's, I think, to allow clearance for metering.

[Ian Grant]

If a 4000$ Leica 21mm isn't better than a 650$ Nikon 20mm...

It's not so much the price rather the design and there's no way of matching the quality of a pure wide angle lens with a retro focus SLR WA design.

A better example although MF not 35mm would be a comparison of the 38mm Biogon on the Hassleblad SWC with the 40mm Distagon for the regular Hasselblads.

Ian

[David Lyga]

Very interesting how retro-focus can actually be an advantage.

Perhaps there will be others with relevant comments on this topic. All I have ever heard is how 'compromised' the SLR wide-angles are but I see nothing but sensational results from such 'inferiority'.

Mark Crabtree: you are very correct to state that focusing them is a problem with SLRs but some are better than others. - David Lyga

[AgX]

AgX: So, (in my mathematical ignorance) does that mean that the 'steeper angles' forgo the need to worry about the edges being less exposed?

Yes David, that was what I meant.

At the Leica-Camera website you'll find pdf's with MTF's for both classic and retro-focus wide-angle lenses. Perhaps they'll make you wiser concerning resolution.

EDIT:
Refering to the subsequent postings, you'll also find there graphics concerning distorsion.

[Mark Crabtree]

Mark Crabtree: you are very correct to state that focusing them is a problem with SLRs but some are better than others. - David Lyga

That's true. I've used some pretty good finders, but they are still dependent on the lens speed. I'm happy with my 35 f2.8 Distagon, but not with focusing it indoors. With a Leica, or similar, that isn't a factor.

[markbarendt]

David,

As far the WA's I've used on my Nikons, all I can say is that it would be highly doubtful that simply substituting Leica gear would have "improved" anything.

I'm not saying a lab could not find something to measure, just that that difference would not have made a significant change in the success of the photos.

If a 4000$ Leica 21mm isn't better than a 650$ Nikon 20mm...

A $4000 Leica Lens is definitely better at being "jewelry".