Sigma SD1 focusing with Sigma 2.8-4 / 17-70mm DC OS HSM Macro

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Milla Magia
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Sigma SD1 focusing with Sigma 2.8-4 / 17-70mm DC OS HSM Macro
6 months ago

After playing with the combination above for a while I would like to share some of my experiences.

All started about my findings that some of my party photos (AF focusing) were backfocused, mainly taken aperture full open. SD1 has the micro adjustment system, so I thought it would be an easy task to correct the not so accurate focusing point. Believe me, it's not easy. After many trials I found out that the precise focusing point varies with the focal length, with the distance of the focusing target, with the aperture and even with the lighting condition. So, it is not possible to adjust the focusing reliably for all shooting situations. If you adjust the focusing point with the micro adjustment to be correct for 70mm macro shot, it will not be correct for 17mm macro shot or for 70mm shot to distance of 2-3 meters. If you shoot the same target from same distance and vary the focal length from 17mm to 40mm and to 70mm, all three shot have different actual focusing points. So if one is in focus, the two others are out of focus. Of course the situation is getting better when you stop down but the problem limits the use of full open or near full open apertures in various shooting situations unless you are able to do the micro adjustment every time you change some of the shooting parameters. Very irritating....

So my question is: is the problem in the lens or in the SD! body or behind the camera?

Sigma SD1
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