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Old May 15, 2007, 4:11 PM   #11
DSG
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Most lenses, even very expensive andhighly corrected ones can suffer from some CAwhenset to their widest apertures butyou canminimise ortotally eliminate CA from thevast majority ofcameralensesby simply stopping down their aperture by a stop or two.

For instance, my Carl Zeiss 85mm f1.4 Planar T* shows a fair bit of CA at f1.4, at f2 its still there but reduced by about 50% and at f2.8 there is no CA at all.

But my Carl Zeiss Jena 180mm f2.8Sonnar only has to be stopped down by one stop to f4 and there is no noticable CA.

Other lenses need to be stopped down to f5.6 before there is no noticable CA.

So its best to experiment to find outthe widest apertureyou can stop down to useon any particular lens is where you get nonoticable CA...Its not a fixed f-stop value,it varies from lens to lens.
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Old May 15, 2007, 4:47 PM   #12
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Actually, the lenses I have that exhibit some CA at certain focal lengths, do so at whatever aperature I use, and it does not vary with the aperature.

To be sure, they are not Zeiss lenses, but my experience is that CA is a function of focal length, not aperature.
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Old May 16, 2007, 10:26 AM   #13
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TCav wrote:
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Actually, the lenses I have that exhibit some CA at certain focal lengths, do so at whatever aperature I use, and it does not vary with the aperature.

To be sure, they are not Zeiss lenses, but my experience is that CA is a function of focal length, not aperature.
I have to disagree.

Normally I only useprime lensesthese days and I try to stay clear of Zooms as most are simplyfar too soft for my liking....Being as prime lenseshave a fixed FL, it is very easy to seewhat happens to any CA the lens is producing as the aperture is stopped down.


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Old May 16, 2007, 1:16 PM   #14
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DSG wrote:
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TCav wrote:
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Actually, the lenses I have that exhibit some CA at certain focal lengths, do so at whatever aperature I use, and it does not vary with the aperature.

To be sure, they are not Zeiss lenses, but my experience is that CA is a function of focal length, not aperature.
I have to disagree.
Normally I only useprime lensesthese days and I try to stay clear of Zooms as most are simplyfar too soft for my liking....Being as prime lenseshave a fixed FL, it is very easy to seewhat happens to any CA the lens is producing as the aperture is stopped down.
Ok. Thanks.
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