Bought a Tamron LD A014 18-200mm f/3.5-6.3 Di-II Lens in mint condition for pretty cheap and everything works great except night time shots at infinity focus has the worst coma I've ever seen like so bad it's not possible. Even in live view I can't even focus on stars because the coma is so bad even stopped way down. Something has to be wrong. Any ideas? I'm using an EOS and have around a dozen other lenses including other tamron lenses and m42 vintage lenses and I have had zero issues with coma before with any of them.
Insanely bad coma with Tamron LD A014 18-200mm f/3.5-6.3 Di-II Lens
Sadly, often "cheap" and "good" don't go together. Given the, to me, insanely wide range of the zoom lend I find not strang it to perform rather badly for coma. For normal diurnal photograhy coma isn't that bad in terms of MTF results and contrast reduction at the typical spatial resolution for daytime photography. I suggest there isn't much you can do except trying your hand on something which is NOT a zoom. As a rule, zoom and nighttime photography don't go together.
The larger the zoom range, the worse the performance with prime lenses having the least distortion. Tamron makes some good lenses, but they have a higher rate of bad samples so to speak. I would return it to the seller or just resell it. The lens has probably been dropped or something because if someone bought it new and it was that bad, they would have returned it I have to believe.
andrea tasselli:
Sadly, often "cheap" and "good" don't go together. Given the, to me, insanely wide range of the zoom lend I find not strang it to perform rather badly for coma. For normal diurnal photograhy coma isn't that bad in terms of MTF results and contrast reduction at the typical spatial resolution for daytime photography. I suggest there isn't much you can do except trying your hand on something which is NOT a zoom. As a rule, zoom and nighttime photography don't go together.
Andrea,
I generally agree with what you've said, but I want to point out that the effect of coma on the MTF has nothing to do with whether the lens is used for daytime or for nighttime imaging. Imaging stars makes the problem jump right out but the type of aberration is more difficult to pin down during the daytime. A lens with coma will still produce "soft" images--even during the daytime. Since coma is a field aberration, the problem will become more pronounced as you move further from the center of the field.
John
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