[Question] Is there any difference between lens for slr/dslr and rangefinder?

[derekphan]

Hi,
As far as I know the two camera systems are quite different, but how about the lenses in term of built, quality and whatever? I heard that the widest we can get in the DSLR system is about 15 - 16 mm equivalent to full frame 35mm. Is it true?

 

[Kin Lau]

On a RF you can put the rear element as close to the shutter as you wish. This helps with the wide angles and also makes the lens simpler to design and build.

On an SLR/DSLR, the extra clearance required for the mirror makes it harder to design and build an ultra-wide. Sigma even has a 12-24mm full-frame zoom with no distortion.

12mm is the widest you can practically go for 35mm without using a fisheye.

 

[derekphan]

Thank, I think widest in rangefinder also 12mm right? How about the quality, is there any difference?

 

[Kin Lau]

At the affordable end, the Sigma 12-24 & CV 12/5.6 are very highly rated. The CV 15mm & 12mm are absolute bargains, and very good. I have a Sigma 15-30 in an EOS mount which is probably one of my sharpest lenses.

Zeiss also has a 15mm in both SLR & M-mount but the price is scary.

Oh yes, the other major difference is that my 15-30 is almost larger than the camera 🙂

 

[jlw]

In theory, the fewer constraints the lens designer has, the better the optical quality s/he can deliver. In practice, there are always some constraints (such as size, weight and cost) so loosening up other constraints makes it easier for the designer to do a good job.

The amount of rear intrusion (distance lens can protrude into camera body) is definitely a design constraint: with SLRs the rear intrusion has to be limited to avoid interference with the mirror. With an RF this dimension is more flexible, giving the designer more freedom to deal with other constraints.

Since RF optics tend to be premium priced, this greater design flexibility seems to show up not so much in the form of wilder specs as in the form of higher quality. To pick one trivial example, my 21mm f/2.8 Kobalux RF lens has much better full-aperture performance than my 20mm f/2.8 AF Nikkor (and is considerably smaller as well.) I can only speculate as to why, but one good guess is that since the Kobalux designer didn't need to worry about providing clearance for a reflex mirror, s/he was able to make a more favorable compromise on the other constraining factors of the design.

 

[pvdhaar]

I think the main differentiator is AF versus non-AF. There isn't a lot of quality difference between manual focus SLR and RF lenses if you consider similarly priced options.

Although common wisdom holds that RF wide angles are better than those for SLRs, this isn't necessarily the case. The retrofocal design of SLR lenses may not lead to the same image charactereristics as RF lenses, but engineers have possibilities to correct problems such as light fall-off much better..

The big divide is with AF lenses. Their build is decidedly less impressive, they have shorter focus throw and sit looser in the barrel. As a result, focus accuracy is dependent on which way the focus ring turns to achieve focus, and this goes for using AF as well as MF settings. I usually stop down 1-2 stops from wide open to compensate sloppy AF performance with extended DOF, which is something I never do with manual focus lenses..