90mm Apo-Summicron-M not apochromatic?

[pippy]

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4 minutes ago, ianman said:

1st man to his neighbour : "Your son's name is written in the snow again!"

Neighbour: "Come on, he's a teenager, we've all done it"

1st man: "Yeah, but it's my daughters handwritting!!"

...but then I thought; "Hang on a mo'!...my own daughter's 16-y-o....so this is very possibly going to happen chez nous sometime soon........"

Food for thought...

But on the upside we don't have too much snow in SE20 so perhaps I've got nothing to worry about!

Philip.

Edited May 18, 2021 by pippy

[lct]

Another attempt at f/2. No hint of purple fringing apparently. Bit of loca? or laca? on the bird's wings perhaps? Don't ask me i can't tell the difference but nailing the exposure seems to be critical as usual (90/2 apo, f/2, A7r2 mod, AF adapt., full frame and 100% crop).

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[LarsHP]

53 minutes ago, lct said:

Another attempt at f/2. No hint of purple fringing apparently. Bit of loca? or laca? on the bird's wings perhaps? Don't ask me i can't tell the difference but nailing the exposure seems to be critical as usual (90/2 apo, f/2, A7r2 mod, AF adapt., full frame and 100% crop).

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Thanks for posting a shot with your M 90 Apo. The bird does show some purple fringing, and it seems to be LoCA since the purple (magenta) color is all around and not in one side only. LaCA should typically be red on one side and cyan on the other.

If you want to do an honest attempt at testing the lens for chromatic aberrations (LoCA and/or LaCA), then shoot something like a billboard with black text on white background; anything with sharp black/white borders. Then make it a bit out of focus, not totally blurred, but like "transition zone" un-sharpness.

Edited May 19, 2021 by LarsHP

[LarsHP]

22 hours ago, adan said:

Sorry, a test of a Leica M lens on a Sony (or a Nikon) sensor stack is junk science. Completely useless (although as with most junk science, it impresses the ill-informed).

A sensor stack has its own "optics" - one or more overlays of glass in front of the sensor - and, with more than one overlay, an included air gap.

Since even "flat" glass refracts light - and so does air, when it interfaces with glass - the sensor cover package can easily degrade and thus misrepresent how the lens itself performs. It can add CA, or curve the field, or otherwise make corners fuzzy.

https://en.wikipedia.org/wiki/Refraction

Leica is supremely aware of this, which is why they have always used a minimalist approach to the sensor covering, ever since the M8: one piece of glass 0.5-0.8mm thick. Two refractive interfaces (front and back, A-G, G-A).

By comparison, the Nikon Z6 uses a three-layer covering (glass/air/glass) totalling ~2.5mm thick. And four refractive interfaces (A-G, G-A, A-G, G-A). It also, per Kolari (who disassemble the things for a living) uses a blurring anti-alias (AA) filter.

https://www.dpreview.com/forums/post/61762254

https://kolarivision.com/nikon-z6-disassembly-teardown/

Not sure what Sony is doing these days - but it was well-known at the beginning of the Alpha mirrorless system that those sensors produced substandard results with otherwise excellent M lenses.

If one wants to test a lens, one puts it on an optical bench and measures the light coming out directly, with no "extra" glass in the system that is not known, calibrated and corrected for the job (e.g. collimator). At worst, one uses a Leica sensor that is designed specifically for Leica M lenses. A random sensor from anyone else is poor lab equipment.

Leica recently redesigned its 28 Summicron, originally calculated "before-digital" in the last millennium, to subtly correct for the minimal effects of even the simplistic Leica sensor covers. Leica designed the S-series (and probably the SL series) lenses to make the sensor glass "a part of the optical formula" from the beginning.

But Leica does not design their lenses to be used on just any old sensor - not their job. People who "adapt" their M lenses to this or that camera do so at their own risk.

So far I haven't seen anyone testing a Leica M 90mm lens and finding it performs worse on a mirrorless camera than on an M camera. Those lenses that have issues are usually wide angle lenses and the issues are in the sides and corners - never in the center. The reason is that the light goes quite straight into the sensor.

You apparently didn't read that my Z6 camera has a Kolari Ultra-Thin converted sensor which has the same thickness as a digital Leica M camera. Using various M lenses on that camera shows that it performs great.

[adan]

25 minutes ago, LarsHP said:

The bird does show some purple fringing, and it seems to be LoCA

The bird is out-of-focus, therefore the purple fringing is not LoCA.

[vanGeist]

vor 40 Minuten schrieb LarsHP:

So far I haven't seen anyone testing a Leica M 90mm lens and finding it performs worse on a mirrorless camera than on an M camera.

I own a 90 Cron pre-Asph and I still prefer it on my M262 than on my a7. It's still a good lens on a Sony body, but an even better one on a decent Leica body. 

[LarsHP]

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44 minutes ago, adan said:

The bird is out-of-focus, therefore the purple fringing is not LoCA.

That is what LoCA looks like when a black and white object is out of focus. In this case the purple fringing suggests that the bird is closer to the camera than the focus point. If you go back in this very thread you will find links where LoCa is explained and demonstrated. Often a ruler with B/W markings is used to show what it looks like in front and behind the point of focus.

Edited May 19, 2021 by LarsHP

[mmradman]

Yawn, how predictable finding fault with lens on different system camera modified by the third party, no surprise results are not as expected.

i have been using APO Summicron M 90mm for about 10 years now, one of my first M lenses, originally on MP (film), M9, M240 and SL601, lately on Nikon Z7.

When I want to use 85-90mm FL Prime lens i prefer it on Leica camera, only complain I have is Moire when I nail the focus, especially in the distance, the lens is deadly sharp.  Also Bokeh balls suffer from ASPH artefacts and serrated aperture blades if slightly stopped down.

For Nikon Z system there is Nikkor Z 85mm f1.8 which is fantastic from max F stop and dirt cheap compared to any Leica lens, I tried both Leica and Nikkor and Nikkor is better on Z camera.

[ZHNL]

5 hours ago, mmradman said:

Yawn, how predictable finding fault with lens on different system camera modified by the third party, no surprise results are not as expected.

i have been using APO Summicron M 90mm for about 10 years now, one of my first M lenses, originally on MP (film), M9, M240 and SL601, lately on Nikon Z7.

When I want to use 85-90mm FL Prime lens i prefer it on Leica camera, only complain I have is Moire when I nail the focus, especially in the distance, the lens is deadly sharp.  Also Bokeh balls suffer from ASPH artefacts and serrated aperture blades if slightly stopped down.

For Nikon Z system there is Nikkor Z 85mm f1.8 which is fantastic from max F stop and dirt cheap compared to any Leica lens, I tried both Leica and Nikkor and Nikkor is better on Z camera.

Not only better on Z camera. It will be better than 90APO in contrast, near range performance and color correction. ( with 90APO on Leica and 85S on Z).  I did the test myself. 
 

90APO has decent color correction but really not better than many latest mid tele in this regard. For example SL cron, Nikon 85S and even sigma 65mm. It has more CA than I like to see for a lens with APO label. I handled multiple copy of this lens, it is normal behavior. Just need align your expectation here. I personally think it is due for change.

I do love 90 APO due to size and rangefinder focus and of course corner sharpness at infinity even wide open but contrast, flare, CA it  need software help compare to best out there. 

[adan]

10 hours ago, LarsHP said:

That is what LoCA looks like when a black and white object is out of focus.

Nope, it is just what color fringing looks like when the subject is out of focus.

LoCA only exists in things that are in focus.

Quote

In optics, chromatic aberration (CA), also called chromatic distortion and spherochromatism, is a failure of a lens to focus all colors to the same point

If you don't know the difference between LoCA and color fringing in general, you need to study a little optical science.

Edited May 20, 2021 by adan

[evikne]

On my modern lenses, I tend to look for flaws and shortcomings. But on my old and imperfect lenses, I look for the positive things.

The latter is much more satisfying. 🙂

[jaapv]

13 hours ago, LarsHP said:

That is what LoCA looks like when a black and white object is out of focus. In this case the purple fringing suggests that the bird is closer to the camera than the focus point. If you go back in this very thread you will find links where LoCa is explained and demonstrated. Often a ruler with B/W markings is used to show what it looks like in front and behind the point of focus.

Err - You forget that by definition CA is in the plane of focus. Fringing is quite a different phenomenon. It is caused by unfocused IR and UV activating the sensor, especially by OOF high-contrast objects  - remember, a lens is only APO for visible light.  Your modified sensor probably has impaired UV and IR filtering.

The M8 was particularly sensitive for this. Remember the typical M8 blue halos around street lights and purple-edged shiny objects?

Edited May 20, 2021 by jaapv
added to post

[pgk]

4 hours ago, adan said:

...... you need to study a little optical science.

And if you do it should quickly become apparent that unlike on a forum where we discuss aberrations as having specific effects, in reality things are far more complicated and various aberrations are usually present to some degree and they overlap and interplay and are reinforced or reduced by sensors and software. Lenses and digital cameras are complicated things. Leica M RF lenses have to stand up purely optically, whereas integrated modern digital lenses use a mix of optics and software adjustments and they will no doubt appear to get better as things progress although adjustments may not primarily be made optically in some ways. An RF Leica lens can only be made better using optical improvements which is a traditional and expensive solution in terms of design and engineering. You pays you money and makes your choice.

FWIW some of my favourite images have been shot with Leicas. The fact that the optics might not be the very best solution technically speaking is to me highly irrelevant when content, composition and lighting are all that could be desired.

[ianman]

50 minutes ago, pgk said:

And if you do it should quickly become apparent that unlike on a forum where we discuss aberrations as having specific effects, in reality things are far more complicated and various aberrations are usually present to some degree and they overlap and interplay and are reinforced or reduced by sensors and software. Lenses and digital cameras are complicated things. Leica M RF lenses have to stand up purely optically, whereas integrated modern digital lenses use a mix of optics and software adjustments and they will no doubt appear to get better as things progress although adjustments may not primarily be made optically in some ways. An RF Leica lens can only be made better using optical improvements which is a traditional and expensive solution in terms of design and engineering. You pays you money and makes your choice.

FWIW some of my favourite images have been shot with Leicas. The fact that the optics might not be the very best solution technically speaking is to me highly irrelevant when content, composition and lighting are all that could be desired.

Wise words indeed. I think Paul's text should be the first two paragraphs of every camera and lens manual, written in bold, with a big border and users should not be able to use their camera before having ticked the "I have read and understood this" box.

[lct]

Interesting discussion. Would you agree with this definition?: « Longitudinal chromatic aberration - Lens fault. Will occur on both film and digitaL. Can be reduced by stopping down. Manifests as complementry-coloured fringes (purple/green) along out-of-focus edges across the whole field; absent at the plane of focus; gradually more pronounced towards the out-of-focus areas. Purple fringes usually occur before, green fringes behind the plane of focus. »

Source: 

 

 

[pippy]

1 hour ago, pgk said:

...FWIW some of my favourite images have been shot with Leicas. The fact that the optics might not be the very best solution technically speaking is to me highly irrelevant when content, composition and lighting are all that could be desired...

P.

[farnz]

3 minutes ago, lct said:

Would you agree with this definition?: « Longitudinal chromatic aberration - Lens fault.

It's not a lens "fault" as such, it's a natural property of glass that needs correction to remove it where it is undesirable.

Pete. 🙂

[lct]

I like you folks . The more i read about loca / laca the less i understand. Never mind it's just me .

[ianman]

8 minutes ago, lct said:

I like you folks . The more i read about loca / laca the less i understand. Never mind it's just me .

Don't worry, it's not just you.

The more i read about loca / laca the less i give a f...

Edited May 20, 2021 by ianman

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Hallo,

Look here: Leica M

[LarsHP]

2 hours ago, lct said:

Interesting discussion. Would you agree with this definition?: « Longitudinal chromatic aberration - Lens fault. Will occur on both film and digitaL. Can be reduced by stopping down. Manifests as complementry-coloured fringes (purple/green) along out-of-focus edges across the whole field; absent at the plane of focus; gradually more pronounced towards the out-of-focus areas. Purple fringes usually occur before, green fringes behind the plane of focus. »

Source: 

 

 

This is what I have been referring to all through this thread.