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Hi astrophotographers, I love wide field astrophoto, so I already did many times astropho with my Canon 700Da and lenses. I've got a problem : the left corners of the photo have deformed stars, apparently coma and astigmatism. The deformations are visible at the same position with different lenses. I attached 2 examples : with a 50mm f/1.4 and with a 70-200mm f/2.8 (last generation). If the problem is the same with any lenses, the problem should come from the dslr. Maybe it could be a tilt on the lense mount ? Please help me, it's a very anoying problem... and I don't know if I can fix this. https://astrob.in/full/418289/0/ https://astrob.in/full/418290/0/ Clear skies, Max |
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Sincerely, it is quite hard to evaluate from those two images: the first one has star trails, the second is out of focus. I can see that in both images stars' shapes aren't uniform, but very difficult to understand. What about the lenses' iris? Do you use it wide open? Do you close it 1-2 stops (it depends on lenses)? There is about no lens which can give you perfect round stars w/o chromatic aberration on the whole field with the iris wide open. Maybe Zeiss Milvus can, but we are talking about 2-3k$ lenses. |
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Alessio Pariani: I use it a little bit closed, f/3.2 for the f/1.4 and f/3.5 for the f/2.8. I know that no lense is perfect but the 70-200mm f/2.8 is one of the most high rang of Canon, about 1400€... it shouldn't have this much deformation. And I saw a lot of pictures done with this lense and they don't have deformation because it's an high quality lense. |
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I have a friend with the same lens (1st gen.) who cannot take pictures with it even at f5,6 or f8, so I'm not so surprised. Every zoom lens has problems of this kind, most at its extreme focal lenghts. No matter how good the lens is. I sold a Zeiss 24-70 f2,8 for its spherical aberration and chromatic aberration. I cannot understand why you do have problems even on your 50mm...  |
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Alessio Pariani: Me too, it's a fixed focal, it should be better... I will try with a CANON EF 85MM F/1.4L IS USm, it's a profesional high quality and fixed focal lense, we will see... |
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| As you can see from my last 3 photos, the Canon 200mm f2,8 L II USM is a great lens, so is the Samyang 135mm f2,0... just in case |
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I do have a cheap telephoto Canon lense 56-200 and compared with expensive Canon 70-200 L (borrowed from my friend). Sorry to say- cheap lense works better for astrophoto. Fixed focal lense may be even better, totally agreed.  |
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Alessio Pariani: Amazing pictures ! |
