Is the amount of CA normal for 50mm APO M?

[lukegao1982]

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Hi,

 

I recently purchased a 50mm Summicron APO M lens, I use it with a M11. I have noticed that the amount of chromatic aberration (CA) from this lens is more than I expected, especially comparing to the 50mm Summilux (latest) that I have, the APO lens produced the same amount or more CA at the same aperture. You can see an example from the picture I attached.

 

Note that I used to own the 35mm and 50mm SL lenses which both are APO, in terms of CA and purple fringing, they were near perfect, I am expecting similar performance from the 50mm APO M lens, am I wrong?

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Edited August 10, 2023 by lukegao1982

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[lct]

3 hours ago, lukegao1982 said:

Note that I used to own the 35mm and 50mm SL lenses which both are APO, in terms of CA and purple fringing, they were near perfect, I am expecting similar performance from the 50mm APO M lens, am I wrong?

Welcome to the forum. I have no experience with SL lenses but my M 50/2 apo can exhibit some color fringing in cases of over-exposure. Seen also with M 90/2 apo in the same cases.

[hmzimelka]

I bought and pretty much immediately returned the 50mm APO last December. I was convinced I had a sub-optimal copy. 

For its price, the 50 APO gave me little to no reason to keep it, not for sharpness, rendering, focus roll off, or novelty. Perhaps try another copy if you can, just to rule out copy variation to some small degree. I didn't have that luxury, so I had to return it. My copy also couldn't reach infinity focus, and the right side of the frame had more astigmatism and was less sharp than the left side. I played the Leica QC lottery again even though I knew better. 😂

 

Original framing.

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Centre crop comparison

 

Another centre crop from a high contrast subject.

 

 

Edited August 10, 2023 by hmzimelka

[jaapv]

If you dislike a lens you should certainly not keep it.

However, one should be aware that purple fringing is NOT chromatic aberration, although it is often mistaken for it. 

Read this article by Imatest  Scroll down a bit.  The better and more precise a lens renders high edge contrast and the higher resolving the sensor (smaller pixels.), or the less effective the anti-blooming of the sensor, the more one will see purple fringing. 

The remedy? Use the slider provided by your post-programming program

Note also that some camera brands, notably Nikon, have correction algorithms built into their firmware, so you will not have this problem to this extent on a Nikon Z, for instance. Leica does not use it, as it introduces a small amount of general image degradation in situations where it is not needed.

Note also that this matter is not settled. You will find contradictory articles on the Internet, as lenses that are not corrected well will also cause purple fringing through axial CA.  For high-quality APO lenses, which have very little CA, that explanation does not hold. In such cases I  stick with Imatest which is the world's leading lens testing company. 

[overexposed]

I have the same effect with my 50APO BC, although its not too much for my taste, but sure when you see its an APO lens, one would expect to have no such effects.

but as jaapv mentioned, there are so many effects, people mistaken them quite alot.

 

still a great lens, but stopped down actually not sharper than my 50 F1 nocti V4, they are pretty much on the same level

[lct]

Effects of over-exposure on Summicron 50/2 apo's color fringing below. Typical LoCa (longitudinal chromatic aberration) apparently. Purple fringes before and green fringes behind the plane of focus. Don't ask me more. Just quoting our colleague Olaf in his interesting article there.

M240 + Summicron 50/2 apo @ f/2, 1/4000s:

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M240 + Summicron 50/2 apo @ f/2, 1/500s:

 

[Stuart Richardson]

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APO is a tricky term, as each manufacturer applies it as they see fit. In this case, I think Leica refers to the colors of light being focusing all at the same spot, at the point of focus. Beyond or before the point of focus, they allow for color aberration. Personally, I find this quite unpleasant for color photography. I primarily use the SL2 and the SL APO Summicrons do not behave this way. I think the M lenses are much more of a compromise due to their small size, even though they are more expensive. Perhaps return the 50mm APO if it does not work for you and give the 50mm APO Lanthar a try? Maybe it works better for you? It certainly is a bargain! I have not tried either in person, however, so I cannot say which performs better from this standpoint.

[lukegao1982]

Thanks for all the responses, returning the lens is not an option now as I bought it overseas, maybe I need to adjust my expectation as this M lens is not at the same level of SL lens (Peter Karbe actually mentioned it in one of the video where he rated the optical performance of latest M lens at 9 and that of SL at 12).

I have also reached out to Leica USA with the same information, just to see what they think, I will update the thread with their response when I get it.

[nitroplait]

1 hour ago, lukegao1982 said:

Thanks for all the responses, returning the lens is not an option now as I bought it overseas, maybe I need to adjust my expectation as this M lens is not at the same level of SL lens (Peter Karbe actually mentioned it in one of the video where he rated the optical performance of latest M lens at 9 and that of SL at 12).

I have also reached out to Leica USA with the same information, just to see what they think, I will update the thread with their response when I get it.

The SL 50/2 APO is twice as big and twice as heavy as the M 50/2 APO. There must be design compromises somewhere in the M version.

[Jeff S]

4 hours ago, lct said:

 Just quoting our colleague Olaf in his interesting article there.

 

 

01af (zero, one, af), not Olaf (o, l, af).  Different guys.

Jeff

[lct]

2 minutes ago, Jeff S said:

01af (zero, one, af), not Olaf (o, l, af).  Different guys.

Jeff

Too complicated for my old brain or fingers, sorry O1af and Jeff, but i believe the link i gave is self explanatory.

[Jeff S]

Just now, lct said:

sorry O1af 

Zero, not capital O. 😉🤪

Jeff

[lct]

1 minute ago, lct said:

Too complicated for my old brain or fingers, sorry O1af and Jeff, but i believe the link i gave is self explanatory.

Oops was not O1af but 01af... too complicated for me decidedly.

[jaapv]

2 hours ago, nitroplait said:

The SL 50/2 APO is twice as big and twice as heavy as the M 50/2 APO. There must be design compromises somewhere in the M version.

There are-on all M lenses. As they are constricted in size due to the viewfinder lens designers cannot make construction compromises like they could with lenses  that can be larger. 

[jaapv]

1 hour ago, lct said:

Oops was not O1af but 01af... too complicated for me decidedly.

But kudos for finding that ancient informative thread. Still very much up to date. 

[jaapv]

1 hour ago, Stuart Richardson said:

APO is a tricky term, as each manufacturer applies it as they see fit. In this case, I think Leica refers to the colors of light being focusing all at the same spot, at the point of focus. Beyond or before the point of focus, they allow for color aberration. 

Indeed, and it will only be APO at three points of the spectrum (Leica uses four). What happens in between is anybody's guess..

[pgk]

On 8/10/2023 at 3:43 AM, lukegao1982 said:

I recently purchased a 50mm Summicron APO M lens, I use it with a M11. I have noticed that the amount of chromatic aberration (CA) from this lens is more than I expected, especially comparing to the 50mm Summilux (latest) that I have, the APO lens produced the same amount or more CA at the same aperture. You can see an example from the picture I attached.

 

Note that I used to own the 35mm and 50mm SL lenses which both are APO, in terms of CA and purple fringing, they were near perfect, I am expecting similar performance from the 50mm APO M lens, am I wrong?

I don't have the 50 APO, however firstly, no lens is perfect, not even APO designated Leica lenses, and secondly, the SL lenses are not 'compromised' in that they do not have to be small and their rear, exit pupil is much further from the sensor as a result of this, so the SL lenses have the advantage of being larger which means that there are less constraints on their optical design. The precise performance differences will be known to their designers an Leica but would be difficult to precisely publish as they would probably require complex explanation.