ZE 50/2 and 100/2 Makro-Planar charts

After looking carefully at the recently-uploaded ISO test charts for these lenses, I noticed that both of these lenses seem to have some contrast issues in the center at all f-numbers, which seems very strange to me. For example:


http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=115&Camera=453&Sample=0&am p;FLIComp=0&APIComp=3&LensComp=727&Cam eraComp=453&SampleComp=0&FLI=0&API=5


and


http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=107&Camera=453&Sample=0&am p;FLI=0&API=2&LensComp=728&CameraComp= 453&SampleComp=0&FLIComp=0&APIComp=3


Notice how in both cases, the edges on the center target (concentric circles) have sharp contrast on both the EF 50/1.4 and EF 100/2.8 macro, but the ZE lenses have a kind of halo effect. Also notice that stopping down further doesn't reduce it.


Any thoughts about this? Many owners of these ZE MPs are quite vocal about how much better their lenses are compared to the respective EF lenses; and if one looked in the corners, I suppose they'd be right. But I must wonder what is going on in the image center. It looks vastly inferior. And please don't start spouting nebulous buzzwords about "microcontrast" and "Zeiss look." I want to talk about possible explanations for the chart results.

Looks like flare. Perhaps Canon

Maybe the studio lighting has changed since previous shots, causing flare?


Anyway - the center of the ZE 2/100 shots have a slight magenta cast @ f/2 and f/2.2, suggesting that the focus is narrowly off.


Except for the soft spot at the center, both Zeiss Makro-Planars soundly trounce the comparable Canon lenses regarding image quality on these test shots.


I own the Makro-Planar 2/50, and can attest to its superb image quality. I previously owned ZE Planar 1.4/50, and was rather disappointed at the performance, regarding contrast wide open and especially the downright horrible bokeh at full aperture approaching minimum focus distance. I upgraded to MP 2/50, and have gotten everything I want from a stellar 50mm. :)

Although there is a possibility of imperfect focus, having seen the care with which Bryan has performed all the testing on all the other lenses, I doubt that this remotely likely. A magenta cast is more often the result of axial chromatic aberration, and its visibility at the fastest apertures in these lenses is consistent with such a cause. And since axial CA can be present even at the point of sharpest focus, I think it is reasonable to conclude that misfocus is not the reason for its appearance here.


Furthermore, to say "except for the soft spot in the center..." isn't very objective. One could just as easily have correctly concluded, "except for softness in the corners, the Canon lenses soundly trounce the Zeiss Makro-Planars." One could even say that because the test charts show a loss of contrast in the center--and therefore the most critical region--of the image, and that this phenomenon is present at ALL f-numbers, that this issue is more detrimental to the overall imaging quality of these lenses. That is to say, it won't matter if the corners are sharp if the center isn't. But I am withholding that judgment until I have a better understanding of what I am seeing--i.e., whether it is a result of testing methodology, or if it is a significant aberration of the lens that will be visible in real-world shooting conditions.


Moreover, if this phenomenon is indeed some kind of flare, why are we only seeing it in the very center of the image, and not anywhere else? The ZE 50/1.4 Planar and the 21/2.8 Distagon don't show the same, either.


If the results I've seen had been from any other lens, I probably wouldn't have bothered to question it, as I consider Bryan's testing to be fairly rigorous and sufficiently precise. The fact that I DO find it odd, and am seeking an explanation for it, means that even I acknowledge the reputation that Zeiss lenses have. However I will not go so far as to defend the performance if its prestige is not consistent with the observed results.

Quote:

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Originally Posted by wickerprints

I acknowledge the reputation that Zeiss lenses have.

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My Zeiss lenses are certainly excellent. But then, mine are microscope objective lenses and those are made at the Zeiss production facility in Jena, Germany. FWIW,Zeiss dSLR lenses are OEM'd by Cosina in Japan.

I believe the slight magenta cast of axial CA is due to a slight misfocus. But - that misfocus would have to be so slight that it would not be the reason for the center softness.


I see the 2/50 and 2/100 charts have been pulled - I guess we will get an explanation for this phenomenon later.





For a color cast indicating that the focus is way off, affecting the result - check most of the Nikon lens reviews - like the Nikkor 135 f/2.

Quote:

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Originally Posted by Trondster

For a color cast indicating that the focus is way off, affecting the result - check most of the Nikon lens reviews - like the Nikkor 135 f/2.

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The numbers on the chart are pretty sharp - sharp enough that I'd say focus cannot be "way off," as you suggest. Rather, I suggest instead that the purple cast is truelongitudinal (axial)CA - the fact that stopping down progressively improves the fringing is consistent with that suggestion. In fact, a slight defocusing would actuallyimprovelongitudinalCA, rather than making it worse. Also note that this is a flat chart - we're not talking about 'bokeh fringing' here. As a side note, technically CA applies only in the plane of sharp focus, since by definition an aberration affects only what is in focus. But as the term is commonly applied, I'd call the fringing on both the Nikkor and the Zeiss lenses longitudinal CA, and not due to missed focus.

Hi Wicker...


I too, always look to Bryan

Quote:

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Originally Posted by wickerprints

And since axial CA can be present even at
the point of sharpest focus, I think it is reasonable to conclude that
misfocus is not the reason for its appearance here.

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I think this makes sense, but in some sense does not contradict what Trondster was saying. Some colors *are* out of focus, not due to operator error but because
the focal plane is not flat in all colors.

Quote:

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Originally Posted by neuroanatomist

My Zeiss lenses are certainly excellent. But then, mine are microscope objective lenses and those are made at the Zeiss production facility in Jena, Germany.

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Mine is an eyepiece, also Zeiss Jena. (Actually, I don't know where it is made, but it's branded "Zeiss Jena"). It is a tiny eyepiece with a narrow field of view. And it is awesome, really.


Never been tempted by Zeiss camera lenses, though. (Okay, well... not much [:)])

Quote:

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Originally Posted by neuroanatomist

The numbers on the chart are pretty sharp - sharp enough that I'd say
focus cannot be "way off," as you suggest. Rather, I suggest instead
that the purple cast is truelongitudinal (axial)CA - the fact that
stopping down progressively improves the fringing is consistent with
that suggestion. In fact, a slight defocusing would actuallyimprovelongitudinalCA,
rather than making it worse. Also note that this is a flat chart -
we're not talking about 'bokeh fringing' here. As a side note,
technically CA applies only in the plane of sharp focus, since by
definition an aberration affects only what is in focus. But as the term
is commonly applied, I'd call the fringing on both the Nikkor and the
Zeiss lenses longitudinal CA, and not due to missed focus.<span class="field-item-description"]

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I definitely agree that the cast is due to longitudinal CA - that is precisely my point.


I am very curious as to how a slight defocusing would improve longitudinal CA, as longitudinal CA typically manifests itself as a magenta cast on one side of the focus plane and a greenish cast on the other side, while the focus plane itself (if the lens is constructed correctly) is without any color cast. I can see this for myself in my own pictures with the Zeiss ZE 2/50, where there is a color cast on objects just outside of the focus plane. If the focus had been spot on, we would not have seen any noticeable longitudinal CA.
If the focus was even more off, the cast would not be as visible, but then the whole image would be really blurry.


A good example of longitudinal CA would be in Photozones review of the Sony mount Zeiss ZA Sonnar T* 135/1.8, where the lines in front of the focus plane are purple/magenta and the ones behind are green. There are also examples in Photozones Nikkor 135/2 review, where crops of pictures just behind and in front of the focus plane show greenish and purple casts.


I agree that describing the focus as being "way off" was a bad choice of words - what I meant was "enough out of focus that it would affect the visible result in the 100% crop shots" - or at least "way off for an image taken for a lens review site", and I still believe that the focus is off in the Nikkor 135/2 review, and that the magenta cast is a very clear indication of just that.


I'd rather call the fringing on the Nikkor lenses longitudinal CA due to missed focus.


The very slight CA on the Zeiss picture could be a very slight focus miss, and/or be due to a slightly curved focus plane or a slight lens defect. The Zeiss lenses are known for pronounced longitudinal CA (in my humble opinion, it is their only weakness), and thus a focus miss would be extra visible. However - the very slight color cast on the Zeiss picture (which now has been pulled) was so slight as to be negligible.





As well - Bokeh fringing, Bokeh CA, Longitudinal CA, Axial CA - are all words for the same phenomenon. You would be able to see "bokeh fringing" or "Longitudinal CA" all over a flat chart, if the entire chart was out of focus - as I believe we see in the crops for the Nikkor 135/2.