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Message: <blockquote data-quote="jfmgb777" data-source="post: 1303626" data-attributes="member: 42168">Rough tests of Sigma 120-400 mm OS, Tamron 500 mm Mirror & Digiscoping set-upUsing Norman Koren's lens testing procedure:<a href="http://www.normankoren.com/Tutorials/MTF5.html" target="_blank">http://www.normankoren.com/Tutorials/MTF5.html</a>I tested three set-ups:<ol> <li data-xf-list-type="ol">Canon 350D + Tamron 500mm f/8 mirror lens;</li> <li data-xf-list-type="ol">Canon 350D + Sigma 120-400 f/4-5.6 OS;</li> <li data-xf-list-type="ol">My younger son's Nikon 80 mm spotting scope + Canon A95.</li> </ol>All were mounted on a Velbon D-700 tripod.  To reduce vibration I used remote release for all shots, and mirror lock-up on the Canon 350D.I tried each of the DSLR lenses at 1600, 800, 400, 200 and 100 ASA, and the Sigma at f/5.6, f/8 and f/11 at focal lengths of 400, 300 and 200 mm.For example only, I attach thumbnails of crops of each set-up, with the Canon 350D at 400 ASA, and the Sigma at 400 mm and f/8 (to match the fixed aperture of the Tamron 500 mm mirror).I also attached the best result I achieved with the Sigma at 400 mm (1600 ASA, 1/4000 s).I leave the viewer to judge the order of merit.</blockquote>