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In this test, I evaluate the performance of the 2870 f2.8 AF at 28mm and compare it to MF. I used a Nikon magnifier as an aide for MF and shot with a sturdy tripod and ball head. I focused manually every MF case and re-focused using AF for every AF case. I did no sharpening and slight levels adjustment. At f2.8 and f4, I took a series of five shots each, forcing the camera to refocus each time; I used the first shot in each series for the MF/AF comparison. At f5.6 and f8, I took one shot each. I used the AF f8 shot for the full-frame image. My conclusion: This lens does noticeably better at 2.8 and 4 than the wide angle primes (20/24/28). At 2.8 and 4, only one shot in each series shows a little softness. You should be OK with AF at all stops, although at f2.8 and f4, I would take multiple shots. AF was achieved very quickly and easily so I believe there was sufficient contrast. A good magnifier is a great aide in getting the sharpest image. I have the Nikon DG2 which is one of the least expensive ones. I believe Minolta and/or Canon make one compatible with Sigma DSLR's. If you get one, invest in one that is high-quality and preferably is at least 2.5 power; the Nikon is 2x. |
