E-M5 unreliable AF behavior

Started Aug 16, 2012 | Discussions thread
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Anders W Forum Pro • Posts: 21,466
E-M5 unreliable AF behavior

I have seen several people complaing about the fact that in ordinary AF mode (selection from a grid containing one, nine or 35 rectangles), the AF area of the E-M5 cannot be made small enough (the one rectangle is still pretty big). I agree with that complaint. Sure, you can go into zoom frame AF (see p. 45 in the manual) and get a slightly smaller frame corresponding to 14x magnification. But this requires you to change to a special VF view where certain things (e.g., the highlight/shadows live view blinkies or the level gauge) are no longer visible. Inconvenient.

However, while doing some experiments with my newly acquired tripod, I discovered another problem, which is worth knowing about since it can in certain situations fool you into setting focus incorrectly. The smallest frame you can set in zoom frame AF is in reality bigger than the camera shows it to be. If, for example, you are taking a picture of a curved convex surface, for example a bottle, a can, or a person's face in semi-profile, and, as would normally be the case, want focus in the center of that surface, the camera will back-focus slightly since it uses a larger frame than the one you think it is using.

The only way I have found to avoid this problem is either a) to switch from zoom frame AF (where the camera shows you the AF frame as a green rectangle) to zoom AF (where the camera magnifies the VF view so that all you see is the content of the selected AF frame) or b) to switch to manual focus.

You can easily verify the behavior yourself by conducting the following experiments.

Experiment 1:

1. Put the camera on a tripod.

2. Go into zoom frame AF and choose the smallest AF area possible (14x magnification).

3. Put a can or bottle in front of the camera and make sure the AF area covers only a small central section of the label on the bottle or can.

4. Perform an AF operation.

5. Switch from zoom frame AF to zoom AF (magnified view).

6. Peform AF again and you will see sharpness improve.

Experiment 2:

1 to 4: Same as in experiment 1

5. Switch to MF.

6. Adjust focus towards shorter focus distance and you will see sharpness improve.

 Anders W's gear list:Anders W's gear list
Panasonic Lumix DMC-G1 Olympus OM-D E-M5 Olympus E-M1 Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS Panasonic Lumix G Vario 7-14mm F4 ASPH +28 more
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