 鲜花( 7)  鸡蛋( 0)
|
i'll just quote here: "Autofocus isn't quite what most people think it is. Phase detect autofocus has always traded speed for focus tolerance. The system looks at a split set of data received at the autofocus sensors, measures the difference, then tells the lens to move the direction and distance it calculates. Lenses are not 100% repeatable (I'm actually amazed at how repeatable they are). If you perform the same infinity to near focus operation 100 times, you will get a bell curve of focus around a central position, not one position repeated 100 times. This was first reported to the public by the late Herbert Keppler in the 80's, I think, and then substantiated in a series of tests by him and his staff in the 90's. The tolerances have dropped since then (and I'm surprised at how small the tolerances now are, as we may be in the sub-micron level with some lenses), but there are still tolerances. Two lenses made from the same factory on the same day from the same parts by the same person may perform slightly differently, which is one reason why we have AF Fine Tune"(Thom Hogan, 2012). ^. G, o( ~$ f$ |* o7 j
4 }% a8 T- T7 f+ }4 X" p* x: n$ d
That is the best scenario assuming that you have a paralleled and ideal object(i.e a big sheet with enough contrast and some patterns) to focus on.
& N/ T" i6 v2 a |
|
狗仔卡
发表于 2012-9-11 22:58
提升卡
置顶卡
沉默卡
喧嚣卡
变色卡
显身卡
楼主
