AF false positives

Started Oct 30, 2016 | Discussions thread
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tt321
tt321 Forum Pro • Posts: 13,681
AF false positives

I've been using my GX80 mainly on relatively stationary and no more than slow-moving subjects with single-box AF, box size smallest or at least quite small, S-AF with focus priority.

Focus priority should mean that the camera would not allow me to take a picture without it thinking AF has successfully locked.

I've found the AF to be noticeably faster for most lenses than my old G3, but also I've got more out of focus shots that cannot be attributed to back or front focus. A good example is a close-up shot with everything in the frame to be within a metre distance and nothing in the frame being in focus, because the camera probably focused to infinity. In fact the entire frame consists of creamy bokeh. I tested again by focusing to infinity and keeping the half-press then releasing on a similarly distanced scene and got a similar creamy bokeh frame, hence the guess. But within the scene, there is nothing further away than a metre to falsely latch on in order to have back focus. This is more like fictitious/phantom focus than back focus.

Obviously more systematic tests are needed to find why and how and establish a statistical relevance. However, this will not be easy as it's not a repeatable experiment. When an obviously OOS scene happens the instinct is to release and re-AF and usually AF will then lock correctly for unknown reasons.

Have they in the interest of speeding up AF relaxed the standard of checking in focus priority mode? Or does the IBIS have anything to do with this?

This probabilistic behaviour, although with a small probability, is not very nice. It seems to happen more with the 45/1.8, my only non-Pana lens. But it's not unknown with the 20/1.7. So far it has not happened with my pair of slow Pana zooms and PL25.

Panasonic Lumix DMC-GX85
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