E-M5: Focusing explained

Started Jul 29, 2012 | Discussions thread
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Timur Born
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E-M5: Focusing explained
Jul 29, 2012

I decided to collect all my current results that were spread and buried in several threads into one. If no more errors are found I will combine this and the "Rattlesnaking" thread into a user article for those people who don't read the forums.

Focus performance - speed and reliability

It should depend on the light of the scene and on your exposure settings. Changing exposure compensation and the accompanying exposure changes of Live View has an impact on auto-focus reliability/performance. When Live View has to push exposure of shadows for on-screen view both Live View and auto-focusing lags (Live View frame-rate drops).

  • Normal AF-S (and the initial AF of AF-C before hunting starts) changes contrast and gradations considerably before focusing and then turn it back to your own settings once focus is acquired. "Zoom AF" (and the later hunting part of AF-C) normally uses the current user settings and a slower focusing motor . Some shadow areas may lead "Zoom AF" to change contrast/gradations, too, though.

  • "Zoom AF" could repeatedly acquire focus on test objects in the shadows where both "Zoom Frame AF" and normal AF-S failed. The hunting part of AF-C also could acquire focus, but only when you let it settle down for a few seconds to stop the hunting. However I found a weaved basket in shadows where "Zoom AF" repeatedly did not acquire focus, while "Zoom Frame AF" and normal focus had no problem focusing.

  • Using negative exposure compensation with accompanying Live View exposure decrease can remove the lag. Of course this will have an impact on the image itself and thus is no solution.

  • Using Frame Rate "High" setting will never lag, but also never increase view of shadows to more than +1 EC (and turn off "Full Time AF"). The increased frame-rate itself may or may not have an impact, too, but it doesn't seem like it does. This will speed up auto-focus in shadows, but may leads to auto-focus failing completely in the very darkest shadows compared to "Normal" Frame Rate.

  • Using Gradations "Low" help to eliminate the lag, but of course has an impact on JPG shooting. Not so much on RAW shooting other than the Live View will be rather dark.

  • On the light side fortunately the E-M5 can still focus even when Live View has long clipped out to pure white (orange if you use highlight blinkies), so there still is something else than just 1:1 Live View = AF going on under the hood. Since blinkies are only a rough indication and often don't show real highlight clipping (even less for RAW) this may be one reason.

  • Using "Liew View Boost" effectively fixes Live View's exposure preview to some auto-settings that are not affected by your chosen Exposure Compensation. This may help against some lag in contrasty situations and where you want to apply positive exposure compensation.

As a major drawback this seriously affects Highlights & Shadow blinkies! And it does not solve lag completely, only "High" Frame Rate really does (and combining both doesn't make much sense then).

  • Release Priority is just a "priority" option, especially in AF-C it still allows to release the shutter even when the image is not in focus (during AF-C hunting that only settles after a few seconds). Sometimes the camera signals false "in focus" even in AF-S and thus lets you take out of focus shots.

  • Using more than a single focus area can cause the camera to hunt the focus forth and back before finally acquiring focus. On some targets it can happen with both 35 and 9 focus areas where 1 focus area focuses instantly (even when 35 and 9 decide to use the central area themselves), and it can happen with 9 focus areas where both 35 and 1 focus instantly. I didn't see the case where it just happens with 35, but wouldn't wonder if that can happen, too.

  • AF-C uses a combination of AF-S focus method and magnified focus method, first it tries AF-S and then it switches to hunting (using the same method as full-screen magnified) while the shutter is held half-pressed.

Even when the green dot is lit constantly you need to wait until the hunting settles/stops and then watch out not to shake the camera too much or getting other motion in frame. The green dot indicates by blinking that the camera detected motion (either camera shake or subjects inside the frame).

  • The green dot and green frame have quite some lag. They signal "in focus" (solid color) some time after focus has already been acquired (I guess something like a quarter or half a second). The audio beep signals "in focus" earlier and correctly.

(end of part 1, part 2 as reply)

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