90mm Apo-Summicron-M not apochromatic?

[LarsHP]

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Thanks to Andrew for your elaborate reply.

Someone in this thread suggested that I should refer myself to how Leica themselves define the "apo" designation. A simple search on the internet didn't find anything from Leica, but today, after adding "leica-camera.com" in the search, I got a useful hit here (quoted in italics below).

APO
Apochromatic and more

The prefix ‘APO’ in the name denotes Leica lenses with the best imaging performance. From telephotos to wide-angles, all Summicron-SL lenses in the SL-System portfolio bear these coveted three letters before their names. For a long time, this distinction was reserved exclusively for telephoto lenses, as only they could achieve the exceptional quality required.

It is now over 40 years since the first APO lens built by Leica made its appearance – the APO-TELYT-R 180 mm f/3.4, in 1975. In 2012, the APO-Summicron-M 50 mm f/2 ASPH. became the first standard lens to bear this prestigious prefix.

Thanks to technological progress, more complex construction and new manufacturing methods employed in the SL-System, the design engineers were able to perfectly maximise the optical performance.

To us at Leica, APO means more than just the correction of longitudinal chromatic aberration, for which the purely scientific definition of the term ‘apochromatic’ stands. Above and beyond this, all other chromatic and monochromatic aberrations must also be optimised to a similar degree. This performance is corroborated by the corresponding MTF curves, and practically reaches the physically possible diffraction limits. Our quality expectations and demands have grown accordingly throughout the many years since the launch of the first APO lens, with the result that today’s APO lenses are fit for whatever the future may bring and deliver persuasive performance in combination with highest-resolution image sensors.

-

The bold and underlined part is obviously saying that Leica uses the apo designation to signify that the out of focus areas should be fully color corrected too when they say "all other chromatic and monochromatic aberrations must be optimised to a similar degree".

I do realize that the link is related to the SL series, but on the other hand the quote makes it clear that here Leica describes how they understand and use the term "apo" in general. They also include both the 180mm Apo-Telyt-R and the 50mm Apo-Summicron-M in the text, which eliminates any doubt.

In the end, judging by the official statement from Leica quoted above, I was not unjustified in my expectations regarding a low level of chromatic aberrations in the out of focus areas (bokeh fringing).

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[jaapv]

On 5/23/2021 at 4:29 PM, farnz said:

Jaap to be referring to the term "APO", rather than the term "apochromatic", which has an unequivocal definition.

Indeed.

[lct]

7 minutes ago, LarsHP said:

Someone in this thread suggested that I should refer myself to how Leica themselves define the "apo" designation. A simple search on the internet didn't find anything from Leica, but today, after adding "leica-camera.com" in the search, I got a useful hit here (quoted in italics below). [...]

This is an article about SL lenses. There is a SL 90/2 apo but it is significantly bulkier. 

[luigi bertolotti]

25 minutes ago, LarsHP said:

 

To us at Leica, APO means more than just the correction of longitudinal chromatic aberration, for which the purely scientific definition of the term ‘apochromatic’ stands. Above and beyond this, all other chromatic and monochromatic aberrations must also be optimised to a similar degree....

-The bold and underlined part is obviously saying that Leica uses the apo designation to signify that the out of focus areas should be fully color corrected too when they say "all other chromatic and monochromatic aberrations must be optimised to a similar degree".  For me, it's not SO obvious : I keep my idea that when they speak of aberrations, they are adressed, computed, corrected, optimized etc, on the focus plane

....

In the end, judging by the official statement from Leica quoted above, I was not unjustified in my expectations regarding a low level of chromatic aberrations in the out of focus areas (bokeh fringing). ... but I understand well your expectation ... the final lesson ? anytime you're on the way to buy a lens which sports the APO qualification.. carrying a premium price onto this, wait and look for real life test...

 

 

Edited May 24, 2021 by luigi bertolotti

[LarsHP]

If "apo" isn't short for "apochromatic", then what is the meaning of "apo"?

In all the papers about Leica lenses that have the apo designation, they use the expression "apochromatic correction".

 

 

3 minutes ago, lct said:

This is an article about SL lenses. There is a SL 90/2 apo but it is significantly bulkier. 

As I wrote in the post above, Leica makes it clear that here they define how they use the term. They even mention the 50mm Apo-Summicron-M in the same context.

[ZHNL]

I think we are not going anywhere for arguing technical term or personal interpolation. The real value of this thread is presenting the information or fact about particular lens but not arguing the tech term, at least that is my take and even bypass some comments and reply here include OP's. (sorry)  

I have seen many modern lenses include Leica own SL cron in this range exceed 90 APO M color correction performance include LaCA and LoCA ( or bokeh fringing, whatever that term you or he called) though I don't know how much these get corrected in hardware or software level individually but they are not rangefinder (so cant be used on M with OVF) and they are not manual focus glasses with real focus/aperture ring and they are not as small and as good build. 

Once you have a good/correct expectation, this will lead a happy ownership  

[adan]

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It is correct that for Leica today, "APO" doesn't mean "strictly apochromatic."

But that is a fairly recent marketing-driven change, probably within the past 15 years or less.

Given that the excellent (and still not improved-on) 50 Summilux-M ASPH was not given the APO designation, but the closely-developed 75 APO-Summicron-M ASPH was. Back then (2004-5) Leica was still "rigorously scientific" about which lenses got the gold star. 

BTW, I used the original 180mm f/3.4 APO-Telyt-R. Definitely APO in the plane of focus. Equally definitely, produced occasional purple or green fringes in the blurry backgrounds. Which also did not have the smoothest bokeh - but what did U.S. Navy intelligence officers (the original "market") care about bokeh?

Crop from 180 APO-Telyt-R on Canon 5D2.

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Edited May 24, 2021 by adan

[jaapv]

1 hour ago, luigi bertolotti said:

 

And it still does not address the difference between M and other Leica lenses. M lenses are size-restricted, which leads to design limitations, and lack adequate electronic correction. An M lens can never be as aberration-free as an SL or TL lens, unless - see below.

As for the Summicron 50 APO, it took Leica eight years to come from the finalisation of the design stage to actual production because of the difficulty and cost of meeting the tolerances needed.  It can hardly be held up as the standard to which other M lenses must be judged, unless we are willing to pay exorbitant (even by Leica standards) prices for new designs - and are prepared to accept a long development time.

[Jeff S]

31 minutes ago, adan said:

Given that the excellent (and still not improved-on) 50 Summilux-M ASPH was not given the APO designation, but the closely-developed 75 APO-Summicron-M ASPH was. Back then (2004-5) Leica was still "rigorously scientific" about which lenses got the gold star. 

 

 

Peter Karbe told David Farkas that the 50 Summilux ASPH is an APO lens, but at the time thought it was “ a bit silly” from a marketing standpoint.

https://www.reddotforum.com/content/2008/09/photokina-2008-day-2-taking-it-easy-and-getting-an-education-from-peter-karbe/
 

Jeff

Edited May 24, 2021 by Jeff S

[lct]

1 hour ago, LarsHP said:

As I wrote in the post above, Leica makes it clear that here they define how they use the term. They even mention the 50mm Apo-Summicron-M in the same context.

As our colleagues said above an M lens is not an SL lens. An M lens needs compromises that an SL lens does not. Best example is the M 50/2 apo you're referring to. Superb compact lens but resistance to color fringing is not its best feature by far. 

[pgk]

It is perfectly possible to have 'apo' lenses with colour fringes on oof highlights. It is also perfectly possible to have none 'apo' lenses which do not.

[LarsHP]

I think the thread has fulfilled its purpose.

I have gotten much more into the concepts of color aberration and correction. It was not my intention for this thread to be about that, but about my (sudden discovery!) of the lens' color fringing in the out of focus area.

Hopefully someone who consider buying the 90mm Apo-Summicron-M will find at least some postings of value. 😃

Or perhaps they may find some interesting perspectives on the term apochromatic and related concepts. 😉

[laowai_]

On 5/16/2021 at 7:52 AM, jaapv said:

[…]
Leica uses four.
[…]

That would be called a superachromat and probably labeled as such.

[jaapv]

12 hours ago, Jeff S said:

Peter Karbe told David Farkas that the 50 Summilux ASPH is an APO lens, but at the time thought it was “ a bit silly” from a marketing standpoint.

This - Leica probably finds it a bit silly.

[jonoslack]

16 hours ago, adan said:

 

But - we can also note how many low-dispersion elements each contains - 4 to 6 (the 90mm ASMA has only 5 elements altogether!). That itself may make some difference.

(future research question: do the recent - and very large - Leica 75mm f/1.25 ASMA (9 elements) and 90mm f/1.5 ASMA (8 elements) eliminate or subdue "color bokeh fringes?")

A classic apochromat focuses three colors in one plane. Outside that plane the colors are convergent or divergent (not parallel) and thus can create color fringes.

It may be possible to use additional glass elements to achieve something similar to telecentricity or orthagonal projection, as regards divergent color rays (as opposed to diverging lines or sizes/shapes) - restore the original parallel color light rays to parallel before they finally leave the lens.

It would not have to be complete or perfect, since the blurring of the image itself will hide residual misalignments (fringes) if they are simply reduced enough.

This (rough) schematic suggests a hypothetical orthapochromatic lens (light rays corrected ("orth" or "ortho") to parallel across all planes, by additional bending). I don't know if it is actually possible, or whether it might introduce other artifacts to the background blurs (!!!!). And it would be larger than a "simple" apochromat.

Whether or not this is actually how Zeiss and C/V do it, "orthapochromat" ("corrected" apochromat) might still be a reasonable name for such a lens, and "orthapochromatic" for such correction. Leica versions: OAPO-Summicron or OAPO-Summilux. And of course one might then create an "orthosuperachromat" as well. But those are, for the time being, "unofficial" designations.

[edit]: It is - interesting - that C/V's logo for their APO Lanthar lenses is red/green/blue lines in parallel.   /  /  / 

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Interesting, and I like you're idea of the Orthapochromatic lens (and these excellent diagrams), but I'm not sure that it's hypothetical, I would have thought you could fairly apply it to the APO SL range of lenses - I've certainly not seen any colour bokeh fringes in any of them. Actually, the 35 APO M is really good too.

I've been following this discussion, which has really helped me to properly understand the situation, reason for chipping in right now is your 'future research' proposition, because it's something I spent a lot of time on a couple of years ago when testing the 75 Noctilux and 90 Summilux lenses. The answer is that they subdue, rather than eliminate colour bokeh fringes. 

All the best

Jono

Edited May 25, 2021 by jonoslack
typos

[LarsHP]

Yesterday evening I did a quick LoCA test with the 90mm Apo-Summicron-M and two other M mount lenses I have, which aren't marketed as "apo" or having "apochromatic correction". I took several shots with each lens and picked one from each lens, where I nailed focus (which is on the "cup" of the espresso handle).

All images are crops from the very center. The RAW files were processed in Photoshop / Adobe Camera Raw and lens corrections fully turned off. Moderate sharpening applied. All three lenses were shot wide open, so there are slight variations in the depth of field. The first image (DSC0961) was shot from a slightly different position which made the reflection in the tip more intense than in the two others. However, we are primarily looking at the in-focus performance here, so no big deal, apart from that we generally expect a slow lens to perform better than a fast lens.

My conclusion is that the difference is negligible. There is a bit of color aberration in all images, and I don't think it is possible to point out the "apo" designated lens just by scrutinizing the chromatic aberrations.

Which is which, do you think? 🤭

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Edited May 27, 2021 by LarsHP

[Robert Blanko]

Interesting comparison. 👍
 

IMHO, the last photo is the technically most clean photo, followed by the second and then the first which falls off.

But we need bokeeeeeh to fully judge the difference!!

[LarsHP]

11 minutes ago, Robert Blanko said:

Interesting comparison. 👍
 

IMHO, the last photo is the technically most clean photo, followed by the second and then the first which falls off.

But we need bokeeeeeh to fully judge the difference!!

The first one shows obvious spherical aberration on the tip, but the two others have more green fringing there. As noted, the reflection on the tip is more intense in that shot, so spherical aberration will be more apparent for that reason.

Edited May 27, 2021 by LarsHP

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Hallo,

Look here: Leica M

[luigi bertolotti]

I like those riddles... 😄 me too think that APO is the 3rd one... 

[pgk]

Can someone post examples of colour edging on oof high contrast 'edges' taken on film please. Just interested to compare them with digital.