Cannot get sharp focus on Sigma 600mm F8.0 mirror telephoto

Started May 7, 2012 | Discussions thread
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W5JCK
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Cannot get sharp focus on Sigma 600mm F8.0 mirror telephoto
May 7, 2012

Does anyone have a Sigma 600mm F8.0 mirror telephoto lens? I just received one I bought on eBay and although the lens seems to be in very good condition and built like a tank I cannot get it to focus at any distance. I'm using a tripod and remote shutter or 2 sec shutter delay. I've tested it with my Canon EOS T1i and my Sony NEX C3. I'm no amateur when it comes to manual lenses or mirror lenses so I know they are finicky, especially the mirror telephotos due to their shallow DOF, but this one never gets a sharp focus at any distance. It gets close, but it always remains a little blurred at its sharpest focus, regardless of distance.

To be clear, I'm using mount adapters to use this Nikon AI mount Sigma 600mm lens to my Canon EOS and my Sony NEX C3. I've got nearly a dozen Nikon AI and non-AI manual lenses that all work perfectly with these adapters and my cameras and each can obtain sharp focus. This is a Sigma lense with a Nikon AI mount so perhaps that is the issue. The seller claims he tested the lens on a Nikon D700 and a Nikon D3 and it worked perfectly.

I planned to use this lens exclusively for astrophotography, but it won't even work for that if it cannot get a sharp focus.
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An astrophotography hobbyist and amateur radio instructor and examiner. Canon EOS T1i and Sony NEX C3. http://www.w5jck.com

 W5JCK's gear list:W5JCK's gear list
Sony Alpha 7 Sony a6000 Canon EF 70-300mm f/4-5.6 IS USM Sony E 55-210mm F4.5-6.3 OSS Sony E 16-50mm F3.5-5.6 PZ OSS +9 more
Canon EOS 500D (EOS Rebel T1i / EOS Kiss X3) Nikon D3 Nikon D700
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