The size of the ASPHs

[michaelwj]

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Aspherical lenses are supposed to be better at correcting various aberrations, and can in theory replace a group of elements with a single element.

Why is it then that apart from the 2.8/28mm ASPH, Leica's ASPH lenses have not resulted in any real decrease in size, and most likely a significant increase in size?

 

The 2.8/21mm ASPH and pre-ASPH are more or less the same size (slight reduction in the diameter, but the E60 pre-ASPH had an oversized front end)

The 50mm and 90mm's all stayed more or less the same size (which is more or less expected as they're not telephoto lens designs).

But the 1.4/35mm and 2.0/35mm both had significant size increases upon becoming ASPH lenses. This is really where it's at and where my question is reallydirected. 35mm lenses really start to intrude into the VF so there is a real need for them to be small. But the 35mm Summicron went from the smallest to largest of its type with the addition of an aspherical element. Likewise with the 35mm Summilux. The size reduction of the 2.8/28mm was huge, so I would have thought that the 35mm lenses could have at least not grown - ergonomically they probably couldn't get smaller.

 

Is this a result of the ultimate pursuit of perfection?

 

 

 

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[tobey bilek]

Speed is the culprit.  Faster lenses need volume.

[michaelwj]

Speed is the culprit.  Faster lenses need volume.

 

 

Sure, but that doesn't explain the growth from the 2/35 pre-asph to the 2/35 ASPH (30% longer), or from the 1.4/35 pre-asph to the 1.4/35 ASPH (34% longer)

Edited November 16, 2017 by michaelwj

[otto.f]

Isn’t that the floating element itself in the 35FLE as in the Summilux 50 asph? This doesn’t explain the Summicron 35 asph indeed.

[michaelwj]

Isn’t that the floating element itself in the 35FLE as in the Summilux 50 asph? This doesn’t explain the Summicron 35 asph indeed.

 

 

IIRC the change from ASPH to ASPH-FLE for the 1.4/35 didn't really change the size that much if at all (the photo in the link in my previous post is the pre-FLE)

Edited November 16, 2017 by michaelwj

[adan]

The equation is - one ASPH surface can replace two non ASPH surfaces. And since no lens element can have just one surface, that won't result in a smaller lens, per se. You can't have 5-and-a-half elements instead of 6.

 

One ASPH surface may, through knock-on effects on lens complexity, result in the same image quality in a smaller size - or produce better image quality in the same size. You can get an improvement one way or the other, but not miracles.

 

That's a gross simplification from beginning to end, of course. Starting with the "one ASPH surface does the work of two non-ASPH surfaces" oversimplification in the first place. Lens design is a much more complicated set of trade-offs, so it's not that cut and dried.

 

The 28mm f/2.8 ASPH got smaller, but did not improve significantly in quality over the previous f/2.8 non-ASPH. IMHO (Contrast went up, but not necessarily resolution. More CA, less coma).

 

The 28 f/2.0 ASPH had no previous version - but did manage to add a stop of speed within the same size as the (then existing) f/2.8 non-ASPH, with comparable or better (depending on taste) IQ.

 

In some cases, the addition of an ASPH surface may simply barely compensate for the loss of some special glass that had too much lead in it to survive ecological regulations. Or was no longer economical for Schott or Hoya to produce in small batches just for Leica.

 

In the case of the 35mms, remember that they were designed early in Leica's learning curve in designing around molded ASPHs - 9-12 years before the 28 Elmarit ASPH. One might suspect Leica learned something in that decade.

 

The 35 ASPHs (especially the Summilux) use an additional design trick, that contributes to their size increases. Study the x-section of the Summilux ASPH, and you will see that in gross structure, it is a complete 7-element double-gauss lens (like the non-ASPH 35s 'lux and 'cron v.4), with two whole elements added, front and back, as "corrective spectacles". The double-concave )( elements.)(

 

https://leicarumors.com/wp-content/uploads/2011/01/leica-summilux-m-35mm-1.4-lens-diagram.jpg

 

About a cm of extra glass, right there. The Summicron ASPH cuts things down to a 5-element "mini-DG" plus two elements, but the back one is really thick. Thus the weight gain.

 

Now, if we compare resolution of the 'lux ASPH to the 'lux non-ASPH at f/1.4 - the difference in quality is not just night and day, it is night and thermonuclear explosion. It took every trick in Leica's book - an ASPH surface and a massive size increase via the extra elements, to achieve that difference.

 

35mm Summilux non-ASPH @ f/1.4 - has massive aberrations, color bleeds and "glow" even in the center - which takes some doing! Not that they aren't useful in "romantic" situations.

 

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Edited November 16, 2017 by adan

[michaelwj]

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Thanks Andy,

 

As usual an excellent post.

I'm aware of most of those details except the specific "corrective lenses" in the 35 ASPHs (I know there were paired negative index groups, but hadn't really thought about it). I hadn't noticed it either but the first 1.4/35 Aspherical has an almost identical lens diagram to the current ASPH. Can we then presume that the current 35mm ASPH lenses all stem from the 1.4/35 Aspherical designed by Walter Watz? (I'm surprised Peter Karbe didn't change his first name to Walter!).

 

So to summarise, in answer to my question of why the 35mm lenses got bigger instead of staying the same size, your answer is that starting with the 1.4/35 Aspherical, Leica changed the way they designed 35mm lenses, from a standard double Gaiss type lens, to adding a pair of negative index groups on each side, which just happened to coincide with (or was made possible by) the introduction of the aspheric lens elements.

[01af]

Why is it then that apart from the 28 mm 1:2.8 Asph, Leica's Asph lenses have not resulted in any real decrease in size, and most likely a significant increase in size?

 

As a matter of fact, most Leica M Asph lenses are the same size as their immediate predecessors, or became smaller.

 

Lenses that got bigger are only a few. And the reason for the increased size is performance. The easiest (and cheapest) way to make a good lens better is to increase the physical size—that's why the Zeiss Otus line of lenses are so huge. Without aspheric elements, the M Asph lenses would be even bigger.

 

Another reason for increased size, in some cases, is floating elements.

[michaelwj]

But did the floating elements actually result is a non trivial size increase? I don't think the difference between the pre-FLE and the FLE 35mm is significant.

For the other FLE lenses there was no ASPH predecessor.

[01af]

But did the floating elements actually result is a non-trivial size increase?

Yes, sure. Of course, it's not the floating glass but the mechanics to control them.

 

 

I don't think the difference between the pre-FLE and the FLE 35 mm is significant.

I think it is. Length has hardly changed but girth has increased.

 

 

For the other FLE lenses there was no Asph predecessor.

The point is—aspheric elements don't increase the size of a lens. Floating elements do. See Summilux-M 50 mm Asph and Noctilux-M 50 mm Asph. Both had predecessors without aspheric elements and without floating elements. Both are bigger than their predecessors. The reason for the increased size is not the aspheric elements.

 

Just because two things appear together (here: increased size and aspheric elements), it doesn't mean that one caused the other.

[Jeff S]

Peter Karbe discussed the optical challenges of the 50 Summilux ASPH. I've posted this before, but it covers several issues noted here... size, aspheric elements, floating elements, as well as glass type, element positioning, etc. A complex affair....

 

https://www.shutterbug.com/content/leica-lens-saga-interview-peter-karbe

 

(See both pages).

 

Jefff

[Ko.Fe.]

I have aspherical element in 35 2.5 Summarit and it isn't big. I also have Jupiter 50 1.5 which is tiny, but sharp enough at 1.5 and outperforming at 1.5 the Summarit 50 1.5.

35 1.4 Zeiss lenses are large, Viogtlander 30 1.4 are small.

 

To me big sized manual focus lens is nothing but lousy design.  

[michaelwj]

The point is—aspheric elements don't increase the size of a lens. Floating elements do. See Summilux-M 50 mm Asph and Noctilux-M 50 mm Asph. Both had predecessors without aspheric elements and without floating elements. Both are bigger than their predecessors. The reason for the increased size is not the aspheric elements.

 

Just because two things appear together (here: increased size and aspheric elements), it doesn't mean that one caused the other.

Floating groups are an entirely different matter. They have nothing to do with the two 35mm lenses that increased size when they included aspherical elements both initially without floating groups.

 

As for the Noctilux, the increase in size could just as easily be explained by the increase in aperture.

 

As a general note regarding girth, the apparent girth of Leica lenses changed with the modern aesthetic of a constant girth over the whole lens length. Previously the lenses tended to taper and appeared smaller (the 1.4/35 pre-asph is a case in point - it appears smaller than its maximum dimensions)

[henning]

I have aspherical element in 35 2.5 Summarit and it isn't big. I also have Jupiter 50 1.5 which is tiny, but sharp enough at 1.5 and outperforming at 1.5 the Summarit 50 1.5.

35 1.4 Zeiss lenses are large, Viogtlander 30 1.4 are small.

 

To me big sized manual focus lens is nothing but lousy design.  

 

The 35 Summarit is also f/2.5. Yes, depending on which sample on which day the Jupiter 50 can indeed outperform the Summarit. Neither outperforms the Summilux ASPH. The Voigtlaender 35/40? 1.4 designs are based on the old Summilux 35 pre-ASPH, so they should be similar in size to that lens and they are. They also perform similarly, so they're in a completely different class than the Summilux 35 ASPH's. The Zeiss 35/1.4 is an excellent lens, but it is noticeably larger than the Leica ASPH's, so they too have trouble keeping the size down. Lousy design??? Please show us who has done better.

 

Price, size, performance. As lens designers have pointed out, including Karbe, you get to pick one at the expense of the others, and on top of that all three factors are asymptotic to a certain level. Leica have set their goals, and given us what they can. 

[michaelwj]

 

Price, size, performance. As lens designers have pointed out, including Karbe, you get to pick one at the expense of the others, and on top of that all three factors are asymptotic to a certain level. Leica have set their goals, and given us what they can. 

 

 

I think they set performance as high as it can be given that the size must be within limits imposed by the rangefinder, and then price falls where it may.

 

As far as big lenses being lousy design (mechanical and/or optical), I agree with Ko.Fe is so much as a lens that impedes too much into the viewfinder is a lousy design, and more consideration should be taken to the usability of the lens.

[lct]

As a matter of fact, most Leica M Asph lenses are the same size as their immediate predecessors, or became smaller. [...]

 

Not sure to follow you here. Comparing asph to pre-asph lenses of same focal length and aperture, most asph lenses are significantly bulkier than their pre-asph predecessor. Lenses like 21/3.4, 35/1.4, 35/2, 50/1.4 or 50/2 spring to mind here. In fact, the Elmarit 28/2.8 asph is the only exception of a smaller asph lens if i'm not mistaken. 21/2.8 and 90/2 asph and pre-asph lenses have more or less the same size and there are no pre-asph versions to 18/3.8, 24/2.8, 24/3.8, 28/2, 75/2 or 135/3.4, let alone 35/2.4, 35/2.5, 50/2.4 & 50/2.5. Comparing the latters to f/2.8 pre-asph lenses, Summarits are indeed small lenses per se but Summaron 35/2.8 and Elmar 50/2.8 are even smaller. Not 100% sure about the Summaron though. 

[Mark T]

I think they set performance as high as it can be given that the size must be within limits imposed by the rangefinder, and then price falls where it may.

 

As far as big lenses being lousy design (mechanical and/or optical), I agree with Ko.Fe is so much as a lens that impedes too much into the viewfinder is a lousy design, and more consideration should be taken to the usability of the lens.

 

I generally agree with you here... But! Not all Zeiss lenses are big (35/2.8, 50/1.5, 21/4.5 etc), and Leica has started making plenty of lenses that impede the viewfinder lately - 28/1.4 anyone? Hate to see the size of this 75/1.25 that has everyone creaming their shorts. I think I read it weighs 1 kg somewhere? This shocks me before even seeing the price!

 

I'd like top see them concentrate on the easy handling, small, and high quality lenses that made them famous in the first place.

[Letin]

I think Leica's recent pursuit (Karbe) in perfection with ASPH also translates to "reproducing images as close to reality as possible". 

 

I have both version III 35mm summicron and recently updated 2016 asph, they behave very differently and produce incredible images in their own special way. While v3 summicron is significantly smaller and so much easier to carry around, I find the new 35 summicron asph with metal square hood also perfect in terms of handling and image quality.

 

New 16' version almost doubles in length/height (with hood) when compared to legacy non-asph versions. From my experience of owning both I guess one can say and justify owning both for very different purposes and reasons. The increase in size becomes insignificant if you treat non-asph & asph as different lenses, different approaches to the art of photography.

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[michaelwj]

I generally agree with you here... But! Not all Zeiss lenses are big (35/2.8, 50/1.5, 21/4.5 etc), and Leica has started making plenty of lenses that impede the viewfinder lately - 28/1.4 anyone? Hate to see the size of this 75/1.25 that has everyone creaming their shorts. I think I read it weighs 1 kg somewhere? This shocks me before even seeing the price!

 

I'd like top see them concentrate on the easy handling, small, and high quality lenses that made them famous in the first place.

As far as the ZM lenses go. The 1.5/50mm is small, but the 2.8/35 is bigger than the 2.5/35mm CV, and is the same size as the pre-asph 35mm summicrons. The 4.5/21mm is about the same size as the 3.4/21mm SA and gives up close to a stop, and bigger than the 4/21mm CV and gives up 1/3rd of a stop. So while they are small for ZM lenses, they're not really that small.

 

And to prove my original point, the modern aspherical lenses are still bigger.

 

I agree with your final statement whole heartedly.

Edited December 14, 2017 by michaelwj

[otto.f]

I think Leica's recent pursuit (Karbe) in perfection with ASPH also translates to "reproducing images as close to reality as possible". 

 

 

 

If that's Karbe's mission I think it has failed. Many lenses of him depict reality sharper than it normally is with the naked eye, let alone the bo-keh of various lenses. How's the bo-keh of your eyes comparing to mine?