Jump to content

90mm Apo-Summicron-M not apochromatic?


LarsHP

Recommended Posts

Advertisement (gone after registration)

12 minutes ago, lct said:

Sorry but you're still comparing apples to oranges. You can only compare a 90/2 M lens to another 90/2 (or possibly 85/2) M lens. 90/2.8 or 90/4 lenses are not the same lenses at all. The only competitor i know of is a lens even more expensive the ZM 90/2. It is bigger, cannot be found new anymore and i don't know if it is better CA wise than the Summicron apo. 

I will repeat myself here:

1) I am comparing LoCA performance, not focal length.

2) Why would an apo designated 90mm Leica lens NOT have the same LoCA performance as another (telephoto) apo designated lens? Your point would suggest that we should expect a lesser performance from a Leica M 90mm f/2 lens than other lenses.

If you don't get it, then it's not my problem.

You appear not to read what I say - or if you do, you don't care. In either case it's useless to continue this, so I will leave it there.

Link to post
Share on other sites

You cannot compare CA per se. You compare it necessarily on a lens and the performance of a lens depends on basic factors like aperture and focal length. It is more difficult to make an f/2 than an f/4 lens obviously. If you're after a lens with very little CA, chose preferably a 90/4, even an old one like the inexpensive Elmar 90/4 or a modern one like the ZM 85/4 that can still be found new i believe.  I have no experience with it though as i like much my Elmar 90/4 macro. I would not swear that it has less CA than the 90/2 apo though. 

Edited by lct
Link to post
Share on other sites

58 minutes ago, LarsHP said:

I will have a look at the 90mm Summicron pre Asph and see if how it performs regarding LoCA.

Definitely more LoCA (reddish) near the focus plane at f/2 (which is why the APO was created to replace it) - and slightly more obvious color purple/green fringes in background blurs as well.

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

......................................

For lct. LoCA will produce a fringe of one color all around a contrasty edge, as in sample above (red in all directions - above, below, left, right sides of the glasses frame). The red is literally focused in a different plane compared to the green/blue and thus "blurring" beyond the nominal dark/light border. it will occur all across the image. Mostly occurs in longer focal lengths.

LaCA (lateral CA) produces a fringe of one color (e.g. red) on one side of a boundary (e.g. a branch) and a fringe of the complementary color (e.g. cyan) on the opposite side.

It is magnifying or scaling different colors to slightly different sizes, rather than focusing them in different planes. It will be zero at the center of the image, increasing more and more as one proceeds to the corners. Most common in wide-angles.

But both can occur in a single lens, if it is poor enough.

 

Edited by adan
  • Like 3
  • Thanks 3
Link to post
Share on other sites

1 hour ago, LarsHP said:

I didn't necessarily prioritize the f/2 aperture above LoCA correction. Thought I would get both.

And there you have the problem in a nutshell - an assumption.  For you, reality didn't meet expectation that was based on assumption and the result is this thread.

 

4 hours ago, LarsHP said:

As I have also explained repeatedly have explained Nikon, I and others don't agree. It seems not to be how the term is understood by experts today. It seems to be the original sense of the term, but today all lenses will be considered apochromatic if you limit the term apochromatic to the plane of focus.

Longitudinal chromatic aberration is only corrected in the plane of focus by an apochromatic lens so Nikon, others and you can disagree all you want but you are arguing against the very Laws of Physics in respect of Refraction and the behaviour of light as it passes through materials with different refractive indices and there can only be one winner in that argument.

Pete.

Edited by farnz
  • Like 1
Link to post
Share on other sites

Wow, all that nonsense text for something you can correct in Lightroom with 3 clicks.

Astonishing how one side cannot recognize the lens is not perfect and the other completely oversells the importance with respect to relevance in everyday shooting.

Edited by insomnia
  • Thanks 1
Link to post
Share on other sites

Advertisement (gone after registration)

14 minutes ago, insomnia said:

Wow, all that nonsense text for something you can correct in Lightroom with 3 clicks.

Astonishing how one side cannot recognize the lens is not perfect and the other completely oversells the importance with respect to relevance in everyday shooting.

That's what I consider reductio ab absurdum.

Pete.

PS, There is no typo in the Latin phrase, it's precisely as intended.

  • Haha 1
Link to post
Share on other sites

That would be the lens correction for chromatic aberrations.

OP, let me know if you want the images removed as they obviously aren't mine :)

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

Edited by insomnia
Link to post
Share on other sites

10 hours ago, adan said:

Definitely more LoCA (reddish) near the focus plane at f/2 (which is why the APO was created to replace it) - and slightly more obvious color purple/green fringes in background blurs as well.

......................................

For lct. LoCA will produce a fringe of one color all around a contrasty edge, as in sample above (red in all directions - above, below, left, right sides of the glasses frame). The red is literally focused in a different plane compared to the green/blue and thus "blurring" beyond the nominal dark/light border. it will occur all across the image. Mostly occurs in longer focal lengths.

LaCA (lateral CA) produces a fringe of one color (e.g. red) on one side of a boundary (e.g. a branch) and a fringe of the complementary color (e.g. cyan) on the opposite side.

It is magnifying or scaling different colors to slightly different sizes, rather than focusing them in different planes. It will be zero at the center of the image, increasing more and more as one proceeds to the corners. Most common in wide-angles.

But both can occur in a single lens, if it is poor enough.

 

Thank you vert much for the clear explanation ! :) 

Link to post
Share on other sites

17 hours ago, insomnia said:

That would be the lens correction for chromatic aberrations.

OP, let me know if you want the images removed as they obviously aren't mine :)

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

You probably didn't read the post stating that I couldn't remove the LoCA in Adobe Camera Raw even though I tried. 

Link to post
Share on other sites

19 hours ago, farnz said:

And there you have the problem in a nutshell - an assumption.  For you, reality didn't meet expectation that was based on assumption and the result is this thread.

 

Longitudinal chromatic aberration is only corrected in the plane of focus by an apochromatic lens so Nikon, others and you can disagree all you want but you are arguing against the very Laws of Physics in respect of Refraction and the behaviour of light as it passes through materials with different refractive indices and there can only be one winner in that argument.

Pete.

You are referring to the historical definition which describe a lens design from 1880. Practically all modern quality lenses, say from around 1980 or so, lives up to focusing three colors at the focal plane. Using the term "apochromatic" or "apo" in that original sense for a modern lens will be like Nissan, Volkswagen or Fiat is saying that this car is an automobile as if it's something special. In modern times, the term is used to distinguish a lens from the rest as having better color correction that others. 

Admin/member Jaap wrote in this thread, that the term now seems to be a marketing consept more than a scientific one. While there is some truth to it, since it's about to which degree a lens is corrected, it appears that lens reviewers and producers use the word to refer to both LaCA, which is often measured, and color fringing in front and behind the plane of focus. I think the reason for that is that such a test is more demanding regarding showing how well the various wavelengths coincide in the axial direction, including point of focus. 

Edited by LarsHP
Link to post
Share on other sites

17 minutes ago, LarsHP said:

You are referring to the historical definition which describe a lens design from 1880.

If you look at process lenses which have very exacting specifications you will find that they are often described as apochromats and their optimum and limit of reproduction ratios are also specified. This is hardly historic. Terms are often mis-used by marketing although in the case of Leica there has been sufficient coment from Leica to suggest that they do not do so when stating apo. For many modern AF lenses which are 'corrected' by the camera it is difficult to appeciate how much correction is optical and how much is software

  • Thanks 1
Link to post
Share on other sites

36 minutes ago, LarsHP said:

Admin/member Jaap wrote in this thread, that the term now seems to be a marketing concept more than a scientific one. 

That is the point, as there is not a standardization rule for it. That would be useful, because it directly influences the pictures one takes. A pure marketing term is the addition "asph.".  That has the same value as listing the kinds of glasses, that are used.

The "L" of Canon lenses has more value for me as photographer. Also not directly visible, but indicating a premium class.

  • Thanks 1
Link to post
Share on other sites

18 minutes ago, LarsHP said:

You are referring to the historical definition which describe a lens design from 1880.

Actually, no, it's the current definition of apochromatic.  If you're going to resort to arguing semantics, have you found out what Leica's definition of apochromatic is?  Surely that must be at the heart of your premise if (as per your thread title) you believe the 90/2 APO-Summicron asph is not an apochromatic lens?  Without Leica's own definition you have nothing to argue over.

27 minutes ago, LarsHP said:

Practically all modern quality lenses, say from around 1980 or so, lives up to focusing three colors at the focal plane.

This is a massive generalisation that requires supporting information before it could be taken seriously.

30 minutes ago, LarsHP said:

Admin/member Jaap wrote in this thread, that the term now seems to be a marketing consept more than a scientific one.

@jaapv will be able to confirm either way but I understood Jaap to be referring to the term "APO", rather than the term "apochromatic", which has an unequivocal definition.

 

Frankly I've lost sight of what you're trying to achieve through this thread so perhaps it's time I put the time I have spent in trying to help you, despite your out-of-hand rejection of everything I've written, to more beneficial use.

If you wish to believe that the 90/2 APO-Summicron asph doesn't deserve its status as apochromatic then it's no skin off my nose so, as our American friends say: "Knock yourself out".

Pete.

PS, no hostility intended.

PPSS, Since you've mentioned "expert opinion" several times along the way perhaps I should disclose that for the past 35 years I have been a professional Senior Design Engineer working as the optical subject matter expert for a company with 40,000+ employees in the optical fibre sector.  But I doubt that that'll make any difference to your trenchant position.

  • Thanks 1
Link to post
Share on other sites

Leica doesn’t claim that all APO lenses they make perform as well as all other APO lenses they make. The SL APO lenses are the ones with the highest performance in this regard without exception compared to their M counterparts. M lenses aren’t perfect. Size is a constraint put at a premium in their design. This poor horse we’ve beaten to death is hardly recognizable as a horse anymore. Why must APO lenses all perform the same? 

  • Like 1
Link to post
Share on other sites

15 minutes ago, insomnia said:

that you tried and failed doesn't mean it's not easily done.

If it's easily done, then I should have been able to do it quickly. You may have a routine doing it, so perhaps easy for you. Most, if not all, lens reviews I have seen say it's trivial to remove LaCA and (more) difficult to remove LoCA.

Either way, it doesn't change how the lens performs regarding bokeh fringing. This thread is about the lens, not how to fix its shortcomings. 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...