What is it with Carl Zeiss lenses?

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paulobro
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What is it with Carl Zeiss lenses?

Unread postby paulobro » Wed May 30, 2007 3:59 pm

I was impressed, quite negatively, with the amount of chromatic aberrations Sony's SAL-85F14CZ displays under propitious circumstances — at any opening larger than 5.6! — both in my KM5D and A-100. To demonstrate it I placed an image at Dyxum:
Image(click on the thumbnail to see the larger image)
where btw you can also see some noticeable purple fringing on one of Kiklop's images, same thread, previous posting.

Not owning one I don't know does the SAL-135F18CZ also present the same problem or is it only related to the Planar design, not the Sonnar, or whatever, but I thought I'd mention it here after seeing samples yesterday from a Sony H9's Vario-Tessar on page 5 of Simon Joinson's review at DPR.

Considering the plethora of problems the SAL-1680CZ also seem to be presenting, I wonder what could be the problem with Sony/Zeiss 'marriage'...

Paulo Brochado

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Unread postby David Kilpatrick » Wed May 30, 2007 4:16 pm

Paulo, the image looks very artificially processed with green posterized haloes round blurred areas and so on. I can not think this is just the lens doing this. It must be a combination of the lens, sensor, and very unusual processing to cope with the extreme exposure and contrast conditions.

David

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paulobro
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Unread postby paulobro » Wed May 30, 2007 4:54 pm

Well, David, indeed the image is intended as 'didactic', a center crop from a larger RAW intentionally processed to 'enhance' the CAs (as I did mention on Dyxum). There's nothing added there though. I can email you the original RAW, btw, or make it available for you at YouSendIt, in case you're interested.

Or as many other example images you may want (from 5D or A100, showing it's not sensor related): the problem is not only easily reproduced, unless you take steps to avoid it it will show in almost any take against the light. Which, of course, is the point of my posting...
Paulo Brochado

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Unread postby David Kilpatrick » Wed May 30, 2007 6:25 pm

Email me a raw file sample to [email protected]. I would like see what this looks like. I am looking for a review of the 85mm f1.4 Zeiss for our next Photoworld issue, obviously with good pix, but as you may realise we are quite prepared to discuss negative aspects of new gear too.

David

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Unread postby David Kilpatrick » Thu May 31, 2007 10:11 am

Thanks for the file Paulo. The problem is common to most internal focusing fast tele lenses including the Sigma 150mm f2.8 macro and 50-150mm f2.8 zoom. You will notice that colour fringes in front of the focus plane, and behind the focus plane, appear magenta and green respectively. What is happening is that the floating element system used for internal focusing is maintaining near apo-chromatic correction in the focus plane, at the expense of increasing longitudinal chromatic aberration in front of and behind the focus plane.

This is a complex issue, but it means that if you took the lens and focused it using its own focus mechanism (internal, or with floating groups) then mounted it on a bellows which could reposition it to focus on a different distance, it would be appear to be a very badly corrected lens with strong longitudinal error. In normal use this error only affects defocused zones and it takes special conditions - such as extreme backlight on an edge - to reveal it.

The artefact which appears in images is a tendency for slightly out of focus detail in front of the focus plane to be more correctly focused by long wavelengths (red light) while shorter (blue) are more diffused and contributed less to the visible core image sharpness. Behind the focus plane, blue light is more accurately focused. In the digital image, the result is magenta tinting of blurred detail close to the camera and green tinting of detail further away. I've been through all this with the Sigma 50-150mm f2.8 which managed to show black lettering on an angled test target as pink and green either side of black focused detail for one of our writers, who was very confused and thought it must be a faulty lens.

This effect is absent in lenses such as the Schneider Apo Symmar or Rodenstock Apo Sironar. It is present wherever the lens design is not symmetrical and fully apochromatic. It only makes itself clearly visible with very fast, longer lenses on the digital medium.

You have processed the image in such a way that this is exaggerated. It is possible to process the image, at full size resolution, to obtain a result which looks as clean as it would on film - where the same effect happens, but you are not able to boost it to view an extreme result.

Here's a full size version of the small file (now on your own space):

Image

In fact the image when processed neutrally to cope with the extreme contrast is pretty good, with an attractive tiny diaphram star of light caught on part of the flower which is in sharpest focus. My processing settings were:

Tone Curve Linear
Space sRGB
Sharpness 25
Colour Noise 50 (this helps reduce chromatic edge effects)
WB as shot 4750 +28
Exposure -2.00
Shadows 0
Brightness +25
Contrast 0
Saturation 0

David
Last edited by David Kilpatrick on Fri Jun 01, 2007 12:04 pm, edited 2 times in total.

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paulobro
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Unread postby paulobro » Fri Jun 01, 2007 12:13 am

Thanks David for the excellent and very informative explanation. It won't make the problem go away, sure, but at least now I'll know what is going on... :lol:

Thanks also for the processing tips. I had managed to get it without the artifacts through somewhat different paths to a somewhat different final product, but my intent here and on Dyxum was to show up the problem: no matter what causes it, it is there, quite noticeable and must be dealt with. And, unfortunately, it mars what would be an almost perfect lens.
Paulo Brochado

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jozphoto
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Unread postby jozphoto » Sun Jun 17, 2007 10:13 am

David Kilpatrick wrote:Paulo, the image looks very artificially processed with green posterized haloes round blurred areas and so on. I can not think this is just the lens doing this. It must be a combination of the lens, sensor, and very unusual processing to cope with the extreme exposure and contrast conditions.

David


David, my monitor is 1440x900, this thread display is way wider than that.

Is there a way I can change the display setting?

Thanks

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Unread postby David Kilpatrick » Sun Jun 17, 2007 6:25 pm

No, you just have to scroll for this large picture. Our normal request is that pictures should be no wider than 800 pixels, and for articles, most images will be within 600 pixels. The photo galleries are also 600 pixels.

If you don't have a scroll bar showing, blame IE.

David

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Unread postby jozphoto » Sun Jun 17, 2007 6:35 pm

David Kilpatrick wrote:No, you just have to scroll for this large picture. Our normal request is that pictures should be no wider than 800 pixels, and for articles, most images will be within 600 pixels. The photo galleries are also 600 pixels.

If you don't have a scroll bar showing, blame IE.

David


Oh I see.
Thanks I am using Firefox

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Jaan
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Unread postby Jaan » Fri Dec 14, 2007 3:12 pm


Oh I see.
Thanks I am using Firefox


Hi
Use right click mouse and scroll image to small
if not getting then install firefox extensions
http://www.khoso.com
Cameras: SONY α 100
Lenses: 18-70mm F:3,5-5,6
Apo Tele Converter 1.4 EX
SIGMA AF MACRO AF + 90mm
Sigma APO 4.5-5.6 135-400mm Zoom


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