A question re the Summilux 50mm f1.4 ASPH (APO?)

[nickd]

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On Thorsten Overgaard's page about the Leica Summilux 50mm f1.4 ASPH, there is an excerpt from a talk David Farkas (then) of Dale Photography had with Mr. Peter Karbe at Photokina in 2008 - I have extracted a few relevant sections from that talk:

 

"... many know of his many years of work on the 50mm Summilux ASPH.

 

... he came up with the modified special double gauss design and how the back half of the lens is identical to the 35mm Summilux-M ASPH f/1.4, while the front half is identical to the Leica 50 Summicron. 

 

... he decided that he needed to design a 75 based on the 50 ASPH design.

 

... keeping everything the same, except for removing one lens element in the first doublet behind the central ASPH element used to correct for aberrations caused at 1.4, he minted the design for the Leica 75 APO Summicron-M ASPH f/2.0.

 

I asked if the design was the same, why the 75 was an APO lens and the 50 wasn’t. Here is a bit of a shocker … the 50 lux ASPH is an APO lens, containing an APO-correction element. But, he thought the idea of an APO 50 was a bit silly so they never put it on the lens or in any marketing materials."

 

Can someone confirm whether the Leica Summilux 50mm f1.4 ASPH is indeed an APO lens - I must assume that it is if Karbe says so.

 

If so, why would Peter Karbe and Leica consider, at that time, an APO 50 as silly and not use it as part of their marketing?

 

A number of years later, the Leica Summicron 50mm f2.0 APO is now considered to be one of the best 50mm lenses available in the world, so why would Leica now not market the fact the Summilux ASPH also contains an APO-correction element?!

 

I'm a little confused. Perhaps someone could enlighten me.

 

Finally, I'm not an Optical Engineer, so I have to ask ... in layman's terms why is an APO lens considered so good?

 

Nick

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[Vec]

APO is just apochromatic. Different wavelengths/colors of light get affected by the diffractive nature of the glass differently. Without correcting for it you'd have every wavelength coming to a focus at a different distance from the focal plane -- this leads to chromatic aberation.

 

The simplest solution is to make an achromat lens which has two wavelengths of light come to focus at the focal plane. Anything else is still out of focus, but it's at least closer to in focus. (As an aside, as a lens designer you can pick the wavelengths that you want to be in focus in all of this discussion.)

 

To go a step beyond, you can configure the lens to have three wavelengths focus on the focal plane. This is known as an Apochromatic lens.

 

You can even go further though and make a superachomat that has four colors focus on the focal plane.

 

Some marketing has ignored the science and slapped "APO" on other things as well if things are "well enough" corrected. What Mr. Karbe is saying is they've corrected the lens to have three wavelengths all focus at the same point. The 50 Lux Asph is a strange bird since not only is it apochromatic, it also has a floating lens group to correct for close focusing like the 35 Lux FLE. You could, I suppose, call it the "50mm Summilux APO Asph FLE" if you really wanted to. Hell, I'm sure most other companies would.

 

More here: https://en.wikipedia.org/wiki/Chromatic_aberration

[pgk]

This lens is an extraordinarily good one. Its designation is quite irrelevant as the results speak for themselves. Its a bit like sticking the word 'turbo' on a car - relevant only if you like having it there. A good car will perform no better with it on.

[lct]

Hard to sell an apo 50/2 more than twice the price of an apo 50/1.4 i guess.

[Jeff S]

Karbe says a lot more interesting things about the development of the 50 Summilux ASPH in this old interview...

 

http://www.shutterbug.com/content/leica-lens-saga-interview-peter-karbe#GXdDQ8alAgYt7y1T.97

 

I particularly like this excerpt where he compares the lens to its predecessor...

 

"Establishing a balance between factors, including performance, size, choice of the appropriate glasses, and production tolerances, required lots of patient development work and numerous experiments and trials. For example, the glass I chose for lens element 3 is of crucial importance in minimizing the secondary color aberration. This glass, formerly made at the Leitz glass laboratory, was for a long time offered by another supplier who had taken over its production. But they had stopped making it, so I had to “encourage” another German glassmaker to literally reinvent this glass type. Today this glass is extremely expensive. Indeed, the material for this lens element alone costs as much as the glass used in all the other lens elements of the Summilux 50mm f/1.4 ASPH! In short, optical design software, as useful as it can be, will not help in choosing the appropriate glass types, especially those used to minimize secondary chromatic aberration."

 

 

Separately, Erwin Puts reminds us that much of the difficulty (and cost) of producing Leica M lenses is not just in the quality of components and performance, but the level of quality given its small size. Unfortunately, we haven't seen that size criterion carry forward to other Leica lens systems like the S and SL...but other factors intervene, e.g., AF.

 

For more on the 50 APO Summicron, Puts writes this, which includes more gems for an optical engineer....   http://www.imx.nl/photo/leica/lenses/styled-4/

 

Jeff

[michaelwj]

Hard to sell an apo 50/2 more than twice the price of an apo 50/1.4 i guess.

Adding APO would also make the identification ring on the front of the lens too crowded.

 

Next we will see an APO Asph 50 summilux at $14000...

[Jobea]

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Adding APO would also make the identification ring on the front of the lens too crowded.

 

Next we will see an APO Asph 50 summilux at $14000...

It's a never ending cycle .... the better just keep getting better

 

 

Sent from my iPhone using Tapatalk

[cirke]

A 50 Noctilux APO

[otto.f]

Yes I know from memory that at the introduction of this lens my dealer told me that the Summilux50FLE is an APO, but they couldn't name it that way because of some technical details. This is what Leica had explained at a training for Leica-dealers in Solms-whatever. The practical proof of this pudding lies in the sharpness of green foliage compared to a non-APO, because green is, of the three basic colors, most out of focus in a non-APO

[albertknappmd]

The lens is truly AMAZING and is both APO and ASPH.

Albert     

[otto.f]

I think the enthusiasm for the asph Summilux 50 is ok with me (I sold mine):

- between the Summicron and the Noctilux it has a very reasonable price because it is way better than the Summicron and not so much less or better and more versatile than the Noctilux

- you must be a bit of a 50-man to get really hooked

[Herr Barnack]

At almost 50% less cost than the 50/2 APO, I would be tempted to attempt struggling through life using the "lowly" 50 Summilux ASPH. 

[epand56]

A 50 Noctilux APO

 

At the cost of one billion dollars