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90mm Apo-Summicron-M not apochromatic?


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3 hours ago, pgk said:

.....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.

Exactly.

Unless we remove the variables of sensors and software, we are not measuring "a lens," but "a system:" lens, sensor, software.

But I need to make a slight clarification on the wording of my previous post (#150). Color fringing in out-of-focus areas is indeed caused by the same core property of glass as LoCA and non-APO performance in sharp areas. Dispersion of wavelengths (colors) of light, just like Newton's prism, or the rain droplets that form rainbows.

But LoCA and apochromatic correction (and for that matter, LaCA (lateral chromatic aberration) are very specific scientific/technical terms limited to measuring and describing that effect in the specific case the focused image.

Does Lars see color fringes in out-of-focus areas? Yes.

Is it caused by dispersion of the wavelengths of light? Yes.

Is it LoCA? No.

Does it mean the 90mm ASMA is not an APO lens? No.

It's one of those Internet things. People pick up on a term, and start repeating it without actually understanding what it means, because it sounds "cool and science-y."

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Apochromatic lenses are designed to precisely overlay three wavelengths (usually in the red, green, and blue wavebands) in the plane of focus.  But the plains and island that you mention are in out of focus areas where it's not reasonable to expect the three wavelengths to coincide perfectly owing to chromatic dispersion, ie the difference in the velocity of propagation of different wavelengths through glass.  The three colours will travel through the lens differently so when the rays pass the p

1) chromatic abberations produce all kinds of color fringes. The only commonality is that the fringes are complementary colors of the spectrum: red-cyan, green-purple, yellow-blue and so on. If the red light wanders away from the correct path (latin: ab = "away," erro - "wander") that results in part of the image lacking in red that should be there (appearing cyan), and parts of the image having excess red that shouldn't be there (appearing red). If one doesn't know that chromatic aberratio

Don't worry, it's not just you. The more i read about loca / laca the less i give a f...

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Posted (edited)

In most lens reviews I have read, where the lens has "apo" in its name, the reviewer describes it as meaning longitudinal (aka axial) and lateral chromatic aberrations are supposed to be particularly well controlled in that lens (presumely according to the manufacturer). 

The reviewer then usually presents images where LoCA and LaCA can be studied. LaCA is often also measured, so numbers and graphs will be shown. However, LoCA is usually not measured, but an image with a kind of ruler with black and white markings is photographed with the ruler placed so we can see how these sharp B&W transitions look in the out of focus areas in front and behind the plane of focus. If these areas look entirely like a grey scale image, the reviewer will be happy and say that "the apo designation is fully justified" or something to that effect. 

In other words, it's common even for very sharp lenses to show LoCA, but a few great lenses have minimized LoCA to be extraordinarily low and are usually called "apo" for that reason.

The 90mm Apo-Summicron-M was made at a time where LaCA couldn't be removed by a click in the RAW converter, so I expect Leica decided to control that as well as possible. And in that regard the made a superb job. I see no LaCA even wide open (at least at longer distances; I haven't checked it at closer distances). 

Edited by LarsHP
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8 hours ago, ZHNL said:

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. 

Thanks for your supportive post confirming my findings. 

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5 hours ago, jaapv said:

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?

Chromatic aberrations is not limited to the plane of focus according to most lens reviews I have seen. 

Regarding UV and IR, there is absolutely none in regular digital cameras and still lenses will show both types of CA. 

For the record, I use a Zeiss T* UV filter on my lenses which cuts sharply at 410nm. I have tested the UT converted sensor, and IR leak is extremely low. I have a 700nm IR pass filter and when shooting in manual at the same exposure, the image with the IR pass filter is practically black with extremely dark tones in the highlights.

Furthermore, when I use my 180mm Apo-Lanthar - and by the way also my Voigtländer 15mm f/4.5 VM lens - there is no LoCA visible. Or color fringing or bokeh fringing or whatever you want to call it which clearly eliminate that it is ablut UV or IR issues. 

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38 minutes ago, adan said:

Exactly.

Unless we remove the variables of sensors and software, we are not measuring "a lens," but "a system:" lens, sensor, software.

But I need to make a slight clarification on the wording of my previous post (#150). Color fringing in out-of-focus areas is indeed caused by the same core property of glass as LoCA and non-APO performance in sharp areas. Dispersion of wavelengths (colors) of light, just like Newton's prism, or the rain droplets that form rainbows.

But LoCA and apochromatic correction (and for that matter, LaCA (lateral chromatic aberration) are very specific scientific/technical terms limited to measuring and describing that effect in the specific case the focused image.

Does Lars see color fringes in out-of-focus areas? Yes.

Is it caused by dispersion of the wavelengths of light? Yes.

Is it LoCA? No.

Does it mean the 90mm ASMA is not an APO lens? No.

It's one of those Internet things. People pick up on a term, and start repeating it without actually understanding what it means, because it sounds "cool and science-y."

Well, the way I use the term LoCA is that most lens reviewers do. In that context LoCA is described and shown as color fringing in the out of focus areas. 

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5 minutes ago, LarsHP said:

Chromatic aberrations is not limited to the plane of focus according to most lens reviews I have seen.

Repeating something does not make it more accurate. Few lens reviewers are optically trained.

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43 minutes ago, pgk said:

Repeating something does not make it more accurate. Few lens reviewers are optically trained.

Sorry to enter late in this interesting discussion... but for me the question is straightforward, at least in strict optical terms : chroma aberration is about different wavelengths to FOCUS on different positions (planes... if we forget the spherical...) : I mean, by logic isn't correct to speak of it in out of focus areas,

This does not mean that one cannot discuss/complain to see colour fringes on OOF objects... and some lenses can show this effect more or less than others... but the basic design of an optical system in itself is based on its behavior when focused... I mean : the Apochromatic correction (if I remember correctly) is usually "targeted" at infinity... and one could analyze if and how much this correction is kept at closer distances; but to speak of loca/laca in OOF areas in my opinion doesn't make much sense... it refers to the general topic of "how a lens does manage OOF"  (to avoid a term I dislike ..."B..eh" 😁) ; i am not aware, as a non expert, if and how lens designers DO afford this topic.

Edited by luigi bertolotti
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Quote from the link below referring to the image here:

"Fringing in the picture is from longitudinal chromatic."

https://physics.stackexchange.com/questions/490325/what-is-the-difference-between-longitudinal-chromatic-aberration-and-spherochrom

This confirms my point. 

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One more:

"Longitudinal chromatic aberration (LCA) occurs when different wavelengths focus at different points along the horizontal optical axis as a result of dispersion properties of the glass. The refractive index of a glass is wavelength dependent, so it has a slightly different effect on where each wavelength of light focuses, resulting in separate focal points for F, d, and C light along a horizontal plane (Figure 2)." 

Figure 2: Longitudinal Chromatic Aberration of a Single Positive Lens (First image posted here.)

Figure 3: Achromatic Doublet Lens Correcting for Primary Longitudinal Chromatic Aberration (Second image posted here.)

https://www.edmundoptics.com/knowledge-center/application-notes/optics/chromatic-and-monochromatic-optical-aberrations/

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1 hour ago, pgk said:

Repeating something does not make it more accurate. Few lens reviewers are optically trained.

Now I have quoted two scientific sources saying what I (and the reviewers) say. That settles it for me.

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28 minutes ago, LarsHP said:
1 hour ago, pgk said:

trained.

Now I have quoted two scientific sources saying what I (and the reviewers) say. That settles it for me.

So where does that leave you with your photography?

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2 hours ago, LarsHP said:

Now I have quoted two scientific sources saying what I (and the reviewers) say. That settles it for me.

Note that the plane of focus is clearly indicated...🙄.  And the explanation is about " resulting in separate focal points for F, d, and C light along a horizontal plane (Figure 2)."  i.e. The writer is talking about IN FOCUS, not out of focus.

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4 minutes ago, pgk said:

Well: https://www.nikonusa.com/en/learn-and-explore/a/products-and-innovation/chromatic-aberration.html and it seems that built in correction is applied plus more via their software. Tricky to figure any uncorrected, purely optical results. So yes, you are probaly right😁.

Interesting indeed. Nikon says that « Newer Nikon D-SLRs have a built-in auto lateral chromatic aberration correction feature. It is automatically applied to images, and is not user selectable ». As an old Nikonian myself i see that as another reason of preferring Leica but i can afford it of course. Young photogs around me take superb pics with Nikon and other more affordable lenses and cameras.

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43 minutes ago, pgk said:

Well: https://www.nikonusa.com/en/learn-and-explore/a/products-and-innovation/chromatic-aberration.html and it seems that built in correction is applied plus more via their software. Tricky to figure any uncorrected, purely optical results. So yes, you are probaly right😁.

Thanks for the link. Here's a quote from it:

"Axial chromatic aberration results in blurred colors in front of and behind the focus position due to the differences in each color’s focal point."

Again, the same definition of longitudinal (which is also called axial) CA. 

Regarding built-in corrections, it's quite like when shooting a 6-bit coded Leica M lens on a digital Leica M camera. Things are straightened out in software in the camera. 

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3 hours ago, pedaes said:

So where does that leave you with your photography?

In this thread we have been discussing a lens and it's optical features (particularly its control of longitudinal chromatic aberrations), not practical photography.

However, in that latter regard, LoCA is unfortunately easily visible in snowy landscapes. This was sceneries that I hoped the 90mm Apo-Summicron-M would do better than my Elmarit-M, but I don't see much difference between those two lenses in that regard. 

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4 hours ago, LarsHP said:

Now I have quoted two scientific sources saying what I (and the reviewers) say. That settles it for me.

If that settles it for you, (and if you think the first is in anyway a real "scientific source"), I wish you luck.

Your first "source" is a crowd-sourced stack exchange. It says so right at the top, "Anybody can ask a question. Anybody can answer. The best answers are voted up and rise to the top"

So about as authoritative and "scientific" as Facebook or Twitter. It is just the opinons of "anybodies" that rise to the top based on how many "likes" (👍) they get from other "anybodies."

If you have a medical question, would you 1) get the opinions of "anybodies" off the street, or would you seek out a trained, and qualified physician?

When the Tromsøysund Tunnel was built, was it engineered based on the "opinions of anybodies" from the Internet? Or was it built by trained geologists and engineers? Who didn't bother to ask for the opinions of the "anybodies?"

If it had been designed based on the opinions of a crowd of "anybodies" pulled off the street corners of Tromsø - would you want to drive through it?

Real science is rigorously peer-reviewed - it is checked and rechecked by other scientists and/or science-journal editors before it is published.

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

The Edmund Scientific article is much better.

It has been peered-reviewed at least twice: First, as material accepted and published by Cambridge University Press, and then again for re-publication by Edmund. It has two named scientist-authors, Eustace L. and Teresa D. Dereniak. Who by putting their names on the work, staked their reputations on its accuracy. They aren't "anybodies."

You can even look up their vitaes: https://www.optics.arizona.edu/research/faculty/profile/eustace-l-dereniak

Unfortunately, that scientific article says nothing at all about out-of-focus areas. The diagrams are very specifically limited only to the plane of focus (focus shift = 0).

Edited by adan
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3 hours ago, jaapv said:

Note that the plane of focus is clearly indicated...🙄.  And the explanation is about " resulting in separate focal points for F, d, and C light along a horizontal plane (Figure 2)."  i.e. The writer is talking about IN FOCUS, not out of focus.

If you read it carefully and check the drawings, "along the horizontal plane" here means along the axis the lens is pointing while "vertical" refers to the plane of focus. 

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