What makes SL Lenses so big?

[pgk]

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M lenses are small, compact and mechanical, manual focus lenses, all of which impose restrictions on the lens designer. SL lenses are large, autofocus lenses which have very different requirements on them, although they do not have the same restrctions which are necessitated by the M body.

There are a number of reasons why they are bigger, one of which no doubt is the needs of autofocus. Complexity imposes its own constraints and there is no single, simplistic explanation for the differences. And as for optical performance, well both current M and SL are both excellent lenses and arguing about which are more excellent is pretty pointless since both will produce technically exquisite images.

[LD_50]

25 minutes ago, Einst_Stein said:

You want to learn real lens design from a spontaneous web discussion like this? Be wise!

The goal of the question is to probe how people think or expect if SL lens can be as compact as M. Apparently, the responses think, to be so, the SL lens will have to lower the image quality (in some way?) or to be more expensive then M lenses! Also, it seems none think AF is the main issue, or  an issue at all.

 

I read your original post. The only useful way to discuss lens size is to discuss lens design. Design includes price, IQ, materials, and features. 

This looks more like thread #5335 from non-engineers claiming the SL should be as small as the Q and the L mount lenses as small as M lenses. 

 

[LD_50]

10 minutes ago, pgk said:

. And as for optical performance, well both current M and SL are both excellent lenses and arguing about which are more excellent is pretty pointless since both will produce technically exquisite images.

I agreed with everything you wrote until this. It’s exactly the optical performance, and the diminishing returns at the high end, that drive the size, weight, and price of high end lenses. 

If you ignore the objective differences in lens performance, “technically exquisite” becomes subjective and you can use a lot of modern smalL and cheap options. 

[pgk]

2 hours ago, LD_50 said:

I agreed with everything you wrote until this. It’s exactly the optical performance, and the diminishing returns at the high end, that drive the size, weight, and price of high end lenses. 

If you ignore the objective differences in lens performance, “technically exquisite” becomes subjective and you can use a lot of modern smalL and cheap options. 

Ummmm. There are numerous examples of excellent lenses ("technically exquisite") which are big and bulky and which have no small and cheap alternatives. Modern, small and cheap are fine but few are anything other than competent designs. Its actually Leica M lenses which often show 'diminishing returns at the high end'. 

[LD_50]

9 minutes ago, pgk said:

Ummmm. There are numerous examples of excellent lenses ("technically exquisite") which are big and bulky and which have no small and cheap alternatives. Modern, small and cheap are fine but few are anything other than competent designs. Its actually Leica M lenses which often show 'diminishing returns at the high end'. 

I think you missed my point. 

[FlashGordonPhotography]

M lenses are constrained by the need to work with a rangefinder. That means they need to block the RF as little as possible. That means design constraints and/or exotic materials to make them work. They also need staggeringly tight mechanical tolerances and they are hand finished. All those things contribute to cost. There a re lots of alternate M lenses made by machines or design clones that are just fine but cheaper. But they’re usually larger, like the Voigtlander APO f2’s are bigger than Leica’s.

SLR and mirrorless lenses have no such constraints so it is easier to build them cheaper or better. It’s also makes sense from a handling point of view to have lenses that balance well on the larger body.

Generally L mount lenses are cheaper and better than their nearest M objective. The M 35 and 50 APO Summicrons are not as good as the L mount versions and the M mount versions are multiple times more expensive simply due to their size. If you start looking at the larger M lenses like the 90mm Summicron it’s very close to the SL APO Summicron. But so is the size. Same for the newer ultra fast Noctiluxes (the older 50 keeps its vintage look. It would be possible to build a better one with modern materials). Generally it’s easy to find an L mount lenses that’s cheaper and has *superior* performance to any M mount lens. I will say that rating lenses purely on how low their aberrations and corner performance is isn’t really a judge of whether a lens is good or not. Optically perfect lenses can be frightfully boring.

AFAIK, there are no autofocus 24x36 format lenses as small as the M’s. All af lenses are larger. But to say they are all huge is plainly false. And they don’t always have to be giants like the SL Summilux. Lenses like the stunning Sigma DGDN f2 primes are really really good. Often matching an M in performance for not much extra weight.

Also M lenses are partly more expensive because Leica knows you’ll pay more for an M lens than an L mount one. They sell them for what they think you’ll pay. Business, marketing and all that.

Gordon

[pgk]

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13 hours ago, LD_50 said:

I think you missed my point. 

I'm not sure what your point was. 'Technically exquisite' suggests an extremely high technical ability which some M lenses deliver but few cheap alternative are really in a similar class. Many SL lenses on the other hand have totally different specifications and to fulfil them have to be big. Of the similarly specified SL/M lenses, their designs still have significantly differing requirements.

[Stuart Richardson]

AF alone does not magically make lenses huge. Just look at the Contax G series lenses. They have AF and are basically the same size and quality of the Leica M lenses available at that time. The increasing demands on image quality and focusing speed are the main driver of size. Not only does a current lens have to target 60% contrast across the frame wide open at 100mp (I think that was Karbe's standard for Leica made L mount lenses, if I recall correctly), it also has to do that while being 100% weather sealed and with near silent high speed autofocus and do it at a price that is less than what people will pay for M mount lenses. In some cases, the price is nearly half. At B&H the 35mm APO M is 9050 dollars, with the 35mm APO L at 5560. It is a tall order. 

As for what are better, in my experience, L mount lenses are better than M lenses in almost every case if you compare like with like. This goes for the Sigma lenses too...in most cases they seem better than the Leica M lenses in my direct testing.  

[Jeff S]

The video I linked above is essentially a two hour tutorial by Karbe, half regarding M lenses and half dedicated to SL lenses. Long, but includes details on every technical design and performance variable discussed here, and many others.  Leica Australia produced a similar video discussion with Karbe, along with about 30 min of additional audience questions. 
 

Edited 14 hours ago by Jeff S

[tom0511]

Am 15.11.2025 um 10:39 schrieb jaapv:

No - it is bigger because it is another type of camera. Not being rangefinder it allows bigger lenses which gives the lens designer more freedom to attain better lenses. So it is the other way around. They are better because they are bigger.

plus weather sealed and AF.

[jaapv]

More like weatherproofed  And not all L lenses. The Sigma C series only have a silicon ring on the mount, for instance.