M9 + 50 Lux Asph - Too much purple fringing?

[luigi bertolotti]

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Same bluish fringing as ArtZ, with Summicron 35 asph wide open... this is just out of LR, but re-processing the RAW I corrected it quite well... I tend to think its sensor-related, and not to be regared as a "defect" but as a physical phenomenon that can be decently attenuated.

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[jaapv]

That looks like CA to me. I don't know the exact set up of your shot, so I can't tell you what kind it is.

 

I don't think that is necessarily true about the MTF chart and the corners.

 

As far as the APO designation, the designer of the 50/1.4 ASPH did go on record saying it was an APO design. However, as thrice pointed out, calling a lens APO doesn't always mean much. I'm guessing some manufacturers use APO when their lens bring 3 wavelengths into focus, even if the secondary spectrum is large. I'm also guessing some manufacturers might do the opposite too; if the secondary spectrum is small, even if only 2 wavelengths are brought into focus, they still call it APO. Those last two are conjectures on my part. However, you must take APO on a lens with a grain of salt.

 

You should read Erwin Puts on the subject, he makes about the same remark. Many manufacturers have a rather loose definition. Leica only calls a lens APO if it is corrected to very high specifications regarding secondary and third spectrums, and the correction goes far into IR., according to E.P.

[tgray]

Makes sense. I've never used a Leica lens that actually has the APO designation, so I can't speak from experience. I do have that one data point about the 50/1.4 ASPH being an APO design. While I do actually own that lens, I mostly shoot B&W, so between that and it's lack of an official designation, I think we'll ignore my one data point

 

thrice says he sees longitudinal CA on the 90 APO ASPH. That, plus my aforementioned lack of Leica APO experience lead me NOT to post anything specific about how Leica applies the designation. I did notice he mentioned something along the lines of what you say in 90 Macro-M review.

[adan]

Leica puts APO in the name of lenses they consider APO - APO-Summicron-90 f/2, 75 f/2, APO-Telyt 135 f/3.4 (R - APO-Elmarit-180 f/2.8, f/3.4, etc)

 

APO is NOT included in the name of the 50 Summilux-M ASPH.

 

Chromatic aberration in lenses always creates color fringes of two opposite colors (magenta/green, red/cyan, blue/yellow).

 

It is easier to see in lateral CA, where the colors occur on opposite sides on any object, then in longitudinal CA, where the colors appear "inside" and "outside" objects.

 

True optical CA will also be visible anywhere there is an edge or point of contrasting tone to the background, not just black branches/leaves/wires against a blownout sky.

 

A blownout sky/window/highlight can always produce edge artifacts all by itself, (as multiple examples already posted on this thread demonstrate) therefore it is the worst possible way to check for what the lens itself is really doing. Gray screen-door wires against a dark interior, or black type on a relatively dim piece of paper or some such is a much better test.

 

True CA (and thus APO performance or lack of it) is also only "defined" in the plane of focus.

 

Many lenses - the 90 APO being one of them, my 75 APO being another, the original APO-Telyt-180mm f/3.4 being a third - will produce green/purple edges to out-of-focus points or highlights - sometimes even to the extent of looking almost like a colored mirror lens. See example (75 ASMA) - note green centers and red edges to blur circles.

 

But this has nothing to do with whether they are APO - i.e., corrected for aberrations IN THE PLANE of focus. Nor is it CA, which is also only defined IN THE PLANE of focus.

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[tgray]

Here is the bit I was talking about APO and the 50 ASPH:

 

david farkas blog

 

To reproduce the relevant bit, quoting David Farkas paraphrasing Peter Karbe, the designer of the 75 Summicron and the 50 ASPH:

 

For instance, many know of his many years of work on the 50mm Summilux ASPH. He is extremely proud of this lens, pointing to the MTF chart and exclaiming that wide open at f/1.4 it resolves 40lp at above 50%. He went into how he came up with the modified special double gauss design and how the back half of the lens is identical to the 35mm Summilux ASPH, while the front half is identical to the 50 Summicron. This was the secret to achieving such performance in a fast 50. Then, he said that one Saturday morning over his first cup of coffee in his kitchen he thought about Mandler. Apparently, after Mandler designed the Noctilux, he used the same design to build the 75 Lux. And becuase the 75 Lux wasn't one of Peter's favorite lenses, he decided that he needed to design a new 75 based on the 50 ASPH design. Shortly thereafter, keeping everything the same, except for removing one lens element in the first doublet behind the central ASPH element used to correct for aberrations caused at 1.4, he minted the design for the 75 APO Summicron ASPH. I asked if the design was the same why the 75 was an APO lens and the 50 wasn’t. Here is a bit of a shocker… the 50 lux ASPH is an APO lens, containing an APO correction element. But, he thought the idea of an APO 50 was a bit silly so they never put it on the lens or in any marketing materials.

[adan]

By comparison, my 75 f/1.4 DOES show true longitudinal CA - cyan centers, red edges, even in the focused areas @ f/1.4.

 

The red image is OOF in the plane where the blue and green images are correctly focused - i.e. not APO. So the red in the highlights bleeds into the shadows, leaving the highlights themselves deficient in red (i.e, cyan).

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[Mauribix]

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Leica puts APO in the name of lenses they consider APO - APO-Summicron-90 f/2, 75 f/2, APO-Telyt 135 f/3.4 (R - APO-Elmarit-180 f/2.8, f/3.4, etc)

 

APO is NOT included in the name of the 50 Summilux-M ASPH.

 

 

According to Mr. Peter Karbe, within his interview made by David Farkas David Farkas Photography Blog: Photokina 2008 - Day 2 - Taking it easy and getting an education

The Summilux 50ASPH IS an APO lens FWIW, you're right then 'cause it's not included in the name, but just becuse it sounded a bit silly to desribe a 50mm lens as an APO lens.

[hoppyman]

I own the 90mm APO-ASPH, which produces longitudinal CA, but not lateral CA. The term apochromatic as it applies to photographic lenses is used quite loosely. Toothwalker explains this on his website as well.

 

And you are correct, if the high contrast overexposed area was slightly in front of the plane of focus, one would get green fringing.

 

Daniel, I've not seen the website you refer to, nor am I an expert on fringing. I can comment on the Leica lens bits.

I understand that Leica is very strict about the APO appellation, whereas it may be used more casually by some others. a bit like the way ASPH. is applied.

The 50 Summilux ASPH. is reportedly an APO design but they never bothered to label it as such since it was ONLY a 50!

I think that the APO Summicron 75 ASPH. is actually a derivative of the 50, not the other way around.

More importantly they are both superb and my favourite two lenses. Solms adjusted mine for my upgraded M8 for free 'Your lenses are good, we can make them better'. Their focus accuracy and performance on both my M8 and M9 is truly superb.

[ho_co]

... Here is a bit of a shocker… the 50 lux ASPH is an APO lens, containing an APO correction element. But, he thought the idea of an APO 50 was a bit silly so they never put it on the lens or in any marketing materials.

There you have it. That's all it takes. Any lens can be made an apo by putting in an "APO correction element."

 

That's hogwash. Ask anybody who has spent five minutes with a lens designer or an optics text.

 

David is a nice guy who has a wonderful ability to communicate. But here he says he is paraphrasing Peter Karbe, and David says that he hasn't much optical knowledge. No offense intended, but that's clear from his lens discussions.

 

Erwin Puts says of the current 50 Summilux (http://www.imx.nl/photo/leica/lenses/lenses/page57.html):

The color correction is excellent, but not of APO calibre. Some red and green color fringing can be detected at high magnifications.

The lens isn't designated "APO" by Leica.

 

Leica doesn't fly fast and loose with technical terms. IIRC, Leica was the first company to produce a telephoto apo for 35mm format, the 180/3.4 R. They take their designations very seriously.

 

"The idea of a 50 apo is silly," is it? How about the Kern apo 50/1.9 Makro-Switar?

 

Get off it guys. Show us where Leica has "gone on record" saying the 50/1.4 aspheric is an apo, or forget it.

[jaapv]

I wouldn't have put it quite like that - but yes. Notwithstanding the 50 lux asph is a fantastic lens, arguably the best fast 50 ever built.

[ho_co]

According to Mr. Peter Karbe, within his interview made by David Farkas ....

Maurizio--

To be more exact, you should rephrase that as, for example:

 

"Peter Karbe reportedly said...";

or

"David Farkas reports that Peter Karbe said...";

etc.

 

We have the report that K said something.

 

We have a record that F says K said something.

 

We do not have a record that K said something.

[ho_co]

I wouldn't have put it quite like that - but yes. Notwithstanding the 50 lux asph is a fantastic lens, arguably the best fast 50 ever built.

 

Jaap--I would strike the "arguably" from your statement.

 

I don't think any other fast 50 is in the same league.

 

 

Ugh. Sorry for the high dudgeon. I'm going to relax now with my favorite singing duo: http://www.youtube.com/watch?v=GnZaGK7DUP0.

[hoppyman]

There you have it. That's all it takes. Any lens can be made an apo by putting in an "APO correction element."

 

That's hogwash. Ask anybody who has spent five minutes with a lens designer or an optics text.

 

David is a nice guy who has a wonderful ability to communicate. But here he says he is paraphrasing Peter Karbe, and David says that he hasn't much optical knowledge. No offense intended, but that's clear from his lens discussions.

 

Erwin Puts says of the current 50 Summilux (Summilux1.4/50 asph):

 

The lens isn't designated "APO" by Leica.

 

Leica doesn't fly fast and loose with technical terms. IIRC, Leica was the first company to produce a telephoto apo for 35mm format, the 180/3.4 R. They take their designations very seriously.

 

"The idea of a 50 apo is silly," is it? How about the Kern apo 50/1.9 Makro-Switar?

 

Get off it guys. Show us where Leica has "gone on record" saying the 50/1.4 aspheric is an apo, or forget it.

 

Howard that seems to me to be rather harshly phrased. I am NOT an expert, only a user, nor have I ever heard of the obscure brand/design that you have mentioned. I am not attempting to argue any optical principles with you either.

 

Clearly other people recalled the statement attributed to Peter Karbe (as I did). Since the comment reported by David was quite specific, unsurprising that users think it is credible.

 

You are telling us here then that David's recollection was faulty and he hasn't much optical knowledge. Then that Peter Karbe didn't comment to this effect and that your optical expertise disproves that the 50 has APO characteristics?

[thrice]

Andy, Longitudinal chromatic aberrations occur parallel to the lens axis, hence sometimes being called axial chromatic aberration. The Cyan/Red fringing particularly towards the corners is lateral or "transverse" chromatic aberration, and occurs perpendicularly to the lens axis.

 

Sorry to flog this site so much but it's better explained on Toothwalker's page than I could.

 

Hi Howard, I know of the Kern 50/1.9 Makro-Switar... It'll cost you almost as much as a 50 lux asph (if you include the alpa adapter) and I don't think it would exceed it in imaging capability... I have not seen it referred to as APO, it certainly is a mythical optic though.

[ho_co]

Howard that seems to me to be rather harshly phrased....

You are correct, and I apologized for that in post #52 above.

 

 

... Clearly other people recalled the statement attributed to Peter Karbe (as I did). ...

I'm among those who have heard the statement many times. I raised the question whether there is some basis to the statement other than David's blog. The only references (to the contention that the 50 Summilux is an apo) posted here refer to David's reminiscence of his conversation with Peter Karbe.

 

 

... You are telling us here then that David's recollection was faulty and he hasn't much optical knowledge. Then that Peter Karbe didn't comment to this effect and that your optical expertise disproves that the 50 has APO characteristics?

Not so.

 

I have no way to know whether David's recollection was faulty or whether he is quoting Karbe accurately. I have no way to know whether Peter told David that the current 50 Summilux is apochromatic. Nor do any of us.

 

I said simply that we are dealing with a second-hand account of an event. We need more information before we can ascribe truth either to David's recollection or to the contention that the 50/1.4 is an apo.

 

Nowhere did I say that I had optical expertise or that anything I knew could "disprove that the lens has APO characteristics."

 

We have two known facts: 1) Leica, who are very particular about their lens designations, do not designate the lens "APO." 2) Erwin Puts says the lens is not an apo.

 

A lot of misinformation becomes gang und gäbe if no one stops to verify it. That's the only point I'm addressing here.

 

Similarly, despite refutation of the contention, some people still believe that Al Gore once said he invented the Internet. Wrong data get picked up and bandied about as true if you and I don't do our job to verify them before passing them on.

[tgray]

quoting David Farkas paraphrasing Peter Karbe

 

ho_co: I quoted the relevant bit from my piece. I think I made it clear that this wasn't the gospel or anything. It was a quote from David Farkas paraphrasing the lens designer. It is definitely 3rd hand information, and clearly none of us can verify David's account of what Peter said. I assumed that was understood by using the phrasing I did. To a certain extent, every interview we read is "so and so reportedly said."

 

If I made other statements to the effect that it most definitely absolutely is an APO design, I didn't mean to overstate the case.

[ho_co]

Hi Howard, I know of the Kern 50/1.9 Makro-Switar... It'll cost you almost as much as a 50 lux asph (if you include the alpa adapter) and I don't think it would exceed it in imaging capability... I have not seen it referred to as APO, it certainly is a mythical optic though.

 

Daniel, thanks. When I was in retail, the Alpa representative claimed it was an apo. But you're correct, I can't find anything to justify the claim, despite a couple references at ALPA KERN 50/1.9 SWITAR VS SUMMICRON - Photo.net Leica and Rangefinders Forum.

 

There I go again, spreading unverified and likely false information. Must be more careful.

 

I also doubt that it would perform as well as the 50 Summilux ASPH. But the late versions did have the sexiest ("Visifocus") depth-of-field indicator I've ever seen.

[thrice]

By comparison, my 75 f/1.4 DOES show true longitudinal CA - cyan centers, red edges, even in the focused areas @ f/1.4.

 

The red image is OOF in the plane where the blue and green images are correctly focused - i.e. not APO. So the red in the highlights bleeds into the shadows, leaving the highlights themselves deficient in red (i.e, cyan).

 

Andy, Longitudinal chromatic aberrations occur parallel to the lens axis, hence sometimes being called axial chromatic aberration. The Cyan/Red fringing particularly towards the corners is lateral or "transverse" chromatic aberration, and occurs perpendicularly to the lens axis.

 

Sorry to flog this site so much but it's better explained on Toothwalker's page than I could.

 

Sorry Andy, I read your post properly now and it does look like loCA in the plane of focus, interesting.

[adan]

No problem - at least it's something new and not a rehash of DoF in cropped cameras.....

 

CA in general is caused by the lens having different effective focal lengths for two or three of the three primary colors (Red, green, blue).

 

In longitudinal/axial CA, as thrice notes and my 75 f/1.4 (non-APO) demonstrates, the focal length variation results in one color being out of focus and blurred, adding a fringe to all edges. Run a Gaussian blur on the red channel of any digital image in photoshop, and you'll get the idea. Tends to occur in longer lenses - fixed by ED, flourite, or other special glass.

 

Compare the simulation below-left to my 75 f/1.4 non-APO sample above.

 

Difficult to correct, since fuzziness is toothpaste already out of the tube - but a hefty does of color NR in the raw processor can sometimes minimize it by blurring the color fringes back into each other without affecting the black/white sharpness.

 

In lateral/transverse CA - the kind we probably see most these days, and the kind easily fixed by "lens corrections" tools - the focal length variation results in one color projecting a slightly bigger or smaller image than the other two, creating color fringes where the images don't line up near the corners.

 

Equivalent to "scaling" one channel in Photoshop so that it is bigger or smaller than the other channels - which is exactly, in reverse, how lens corrections plugins or tools fix it. Found in the whole range of focal lengths, but wides especially.

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Hallo,

Look here: Leica M

[Chris_R]

I had an Alpa with the 50/1.9 Makro-Switar. It was not marked APO but it was a great lens.

I remember thinking I could pick out the Leica and Alpa slides from the Nikon, Canon, and Minolta I had shot over the years. I could not tell the Alpa from the Leica though. The best 35 mm reflex I ever had. The person who robbed my house many years ago probably sold it for 50 bucks or threw it away.

 

Cheers

Chris R