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 yesterday at 04:58 PM 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.

[Jon Warwick]

23 hours ago, Stuart Richardson said:

 

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.  

Re: Sigma, my only experience is my DG DN 50mm 1.4 on an SL2-S, but I find it has better (more consistent) edge-to-edge performance than an M 50 APO Summicron on my M11. I’ve also tested an SL3 and SL 50 APO, and again the edges are superior than the M 50 APO on my M11.

I suspect the compactness of M-mount lenses make it an uphill battle for maximum performance, whereas this longer more telecentric Sigma (and SL APO Summicrons) are laying down the data more straightly into the pixel wells?

As an aside, I’m finding it interesting to discover how some resampling software works better with the SL system, perhaps again because the underlying data is so precise? I find that I can’t use Adobe’s Super Resolution with my M11 DNGs (it creates a hyper sharpened and fake look a lot of the time), but it works far better for my taste on both the SL2-S and even SL3 files (ie, not hyper sharpened and digital looking, instead it often creates more apparent resolution and less aliasing). 

Edited 10 hours ago by Jon Warwick

[Stuart Richardson]

I think the SL system demonstrates what the S system did to me when it came out: the importance of synergy in designing a camera system in the current era. The SL was built from the ground up most likely in 2013-2015 and the lenses were matched perfectly to the body, and the body to the lenses. The M system is lovely to use, but it is using 1950s era focusing and mount design to try to work with a 2020's sensor. It's like taking a modern engine and putting it into a 1950s car design. Even if you are making it all new in 2025, there are some constraints that are just inherent in the design. The SL system has the distinct advantage of having all the components designed together. This was also the most successful part of the S system: though it was more or less a closed system, because it was all done at once the lenses and bodies worked so seamlessly together to create impeccable image quality. 

[LocalHero1953]

Manual lenses, M included, have one advantage over AF lenses when it comes to design: they don't require lightweight focusing elements, i.e. one less design constraint. One could guess (but what do I know?) that the best Leica L-mount lenses are slower focusing than Sigma or Panasonic equivalents (original or repackaged) because Leica is less willing to make the compromise to achieve the fastest focusing.

[jaapv]

Maybe, especially for long lenses, but  for short and middle focal lengths there cannot be much of a difference and Leica is not really into longer focal lengths. Except for the 90-280 and that one is not a clone. 

[adan]

On 11/15/2025 at 8:26 AM, Einst_Stein said:

.....people are avoiding to say it explicitly the SL lenses are better in image quality. It’s funny, but it’s OK, I get it!

You want explicit? Here is explicit!

Size (and by extension, roughly weight) vs. MTF performance. Certainly AF plays a role also, but if it were the only factor, the APO-Summicron-SL could be a lot shorter.

(BTW, the Summicron-M v.4 will always be my choice - but facts are facts.)

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