Sigma 30mm F1.4 misfocus question

Started 2 months ago | Discussions thread
glassoholic
glassoholic Senior Member • Posts: 4,051
Re: Sigma 30mm F1.4 misfocus question

Are you running FW 1.2 for the lens? FW 1.3 for the camera?

Are your other lenses also fast and with shallow DOF? (As demanding). Slower lenses tend to be fine as the greater DOF masks errors. Some cameras do tend to be worse than others. I think  the Pen F has had some criticism with f1.2 Oly lenses. The Oly EM1.2 was noticeably improved after a major FW Update. Some third party lenses, or even Pana on Oly bodies, and vice versa, can be more temperamental.

S-AF can be a touch out with fast lenses. C-AF, especially when adjustable like only on the EM1/ X series (PDAF) can (is) be more reliable.

At very close distances, be careful of your body to subject distance varying (rocking backwards and forwards slightly) with S-AF as focus is locked a fraction of second before exposure and with shallow DOF fast lenses, enough for focus to drift out just before you expose.

I have asked before why S-AF can be "out", considering it is reading focus (CDAF) off the sensor, but without explanation. I have also noted that the problem is worst with a single, small AF point... exactly when the AF system is supposed to be the most accurate. My experience is with Oly EM1 series and X cameras... but I have noted questions from Pana owners as well.

I am resigned to the presumption the current technology is not perfect (but better than DSLR PDAF focus).

The slight misses in S-AF are usually only noticable when pixel peeping at 100 or 200%, and at medium or longer focus distances where one can usually stop down a stop or two which "covers up" errors with DOF. At closer distances, where the small AF point has more subject matter, there is usually not a problem. For many people, they will consider the focus perfect, as they don't view at 200%. Others will be annoyed it is not spot on.

I just accept and adapt... either via tuned C-AF on Oly EM1/ X series cameras, or stop down a stop or two, and learn in what situations it is likely to occur, and be careful and take enough shots.

Good luck!

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