What make RF lenses smaller than their SLR counterparts

[250swb]

Mirrorless camera lenses can be more compact because optical corrections can be done with in-camera software. Equally they can be bigger and use software to allow for better image quality at each end of a wide zoom range, 24-200 for example, where image performance of traditional SLR lenses often degraded at the limits.

I think the answer regarding SLR lenses being larger lies between form and function (the average balance and weight on the camera body), the aperture stop down mechanism, and price. Common sense says all three elements need to be worked in harmony. When Nikon made the F the last thing they wanted was a camera that was fiddly to use, overly complex, or too expensive. On the other hand when the Leica rangefinders were invented there wasn't much extra technology around to load onto cameras so there was no reason to make them bigger. The general smaller size was set in stone by never needing the stop down mechanism and there wasn't a mirror to avoid. The hidden advantage over the years though was that it allowed rangefinder cameras to be used in different ways to SLR's, and they could be combined in warzones where many photographers had one or more of each around their neck. Form and function came back to bite Leica with the M5 where the majority of users said 'too big, not interested'.

 

[koraks]

Mirrorless camera lenses can be more compact because optical corrections can be done with in-camera software.

The difference is/was also there when SLR's were purely mechanical.

Btw, I stand corrected on my earlier comment re: @halfaman that he would be wrong about the aperture aspect. Having read @Mark J's excellent posts, I realize now that @halfaman was probably referring to the actual physical size of the aperture assembly as such - not the 'virtual' aperture size 'as projected through the front element'.

I think the answer regarding SLR lenses being larger lies between form and function

See @Mark J's posts above; there's more to it. I think we've all noticed it with wide angle lenses, which are surprisingly compact on RF cameras, or surprisingly bulky on an SLR - provided they're optically corrected with the same efficacy. Yes, fairly small 28/2.8 etc. SLR lenses have been available for eons, but their barrel distortion has always been significant, while a 15mm (!) Voigtländer RF lens seems to be virtually free of any distortion. Getting somewhat similar performance from an SLR lens at the same focal length results in a massive chunk of glass.

 

[Mark J]

Mirrorless camera lenses can be more compact because optical corrections can be done with in-camera software.

This was already being done in SLR's before mirrorless cameras hit the market. In Canon's range, for example, the 5D Mk.II has none but from the 5D Mk.III onwards it is used

 

[Mark J]

I realised yesterday that there is another factor which does have an effect and perhaps more for the longer zooms or teles.
The exit pupil distance ( the apparent distance of the stop, when viewed from the rear of the lens ) is more constrained on an SLR. It cannot be too far forward ( eg. with a tele ) , because it has to work with the optical design of the viewfinder, and if not controlled, you lose brightness in the corners of the viewfinder.
Most teles, particularly MF ones, would rather have the stop nearer the front element if they could. I would ease correction of lateral colour, and reduce the amount fo full aperture vignetting.
With mirrorless, I suspect ( though I'll defer to anyone who has hands-on design experience ) that the exit pupil distance is a bit more flexible.

 

[Sirius Glass]

SLRs are larger than range finders because the lens needs to be further from the film plane to avoid the mirror impacting the back of the lens. Furthermore the prism and mirror assembly adds to the weight.

 

[JerseyDoug]

Early 35mm cameras were small rangefinders and the lenses were small to match. Over time larger 35mm SLR cameras became more popular. This gave lens designers freedom to increase the size of lenses to add functions or improve optical performance.

 

[Dan Fromm]

Early 35mm cameras were small rangefinders and the lenses were small to match. Over time larger 35mm SLR cameras became more popular. This gave lens designers freedom to increase the size of lenses to add functions or improve optical performance.

Huh? Please read this thread from the beginning. Earlier posts gave real reasons, such as different optical designs (wide angle lenses, larger maximum apertures, ...) and different mechanical designs (aperture stop down linkages etc.). SLRs didn't add freedom, they removed it because of larger flange-focal distances.

 

[Mark J]

Yes.
However there is a good point there from Doug but it's not the same as the original question.
One area where lens design is easier for Mirrorless compared to RF, is that there is no issue with viewfinder blocking.
Hence you are free to design zooms and high-aperture lenses without restricting the diameter or length.

 

[Luckless]

Yes.
However there is a good point there from Doug but it's not the same as the original question.
One area where lens design is easier for Mirrorless compared to RF, is that there is no issue with viewfinder blocking.
Hence you are free to design zooms and high-aperture lenses without restricting the diameter or length.

This is an important factor in product design. There is no such thing as a singular "perfect", everything is just a long series of compromises to reach a reasonable goal for a given task.

Function and Form are interdependent. One has to at least follow the other, but choices for one feed back to impact the other.

 

[ic-racer]

I have a Lithagon (early retrofocus) on my Edixa. I think the Angenieux was patented in 1953 and the Lithagon patented in 1960.

 

[chuckroast]

Early 35mm cameras were small rangefinders and the lenses were small to match. Over time larger 35mm SLR cameras became more popular. This gave lens designers freedom to increase the size of lenses to add functions or improve optical performance.

View attachment 369590

I don't entirely agree with this. It's certainly true that the larger footprint allowed things like autofocus and better zooms to come into existence. But in a like-for-like comparison those old RF lenses hold their own against modern primes, at least in some cases, and when shooting monochrome. (I've not checked with color.)

For example, I have a LTM Collapsible Summicron 50mm f/2, a Summicron-M 50mm f/2 V3, and a Nikkor 50mm f/1.4 Ai-S. There is not a huge difference among them. There are slight differences in "look", but if anything, the Nikkor performs less well than the Summicron-M.


Similarly, you'd be hard pressed to see a clear and compelling winner between the Nikkor 35mm f/1.4 Ai-S and the Summicron-M 35mm f/2 ASPH.

I realize this isn't exactly a heads up comparison which would require comparing to the 50mm and 35mm Summilux respectively, but I don't have that kind of money ...

 

[Bill Burk]

M42 didn’t always have the pin or the aperture follower so that can’t be the reason.

I agree that making room for the mirror was a big reason. But look at the difference in these: 50mm f/1.5 Sonnar for Contax. Doesn’t even need a helicoid! Next to 50mm SMCT and banana for scale.

 

[Mark J]

Top marks on using a banana for comparison.
I'm not familiar with the Pentax lens, is it f/1.5 and also a rangefinder lens ?

 

[Alan Edward Klein]

Isn't the reason because the film is further back?

 

[Bill Burk]

Top marks on using a banana for comparison.
I'm not familiar with the Pentax lens, is it f/1.5 and also a rangefinder lens ?

It’s the f/1.4 normal lens that came with my dad’s Spotmatic II

 

[Mark J]

OK good, so that's an SLR lens. The contax is unusual in not needing a focus helicoid.
Bear in mind that just going from f/1.5 to f/1.4 will increase a lens's bulk and weight by over 20% .