5N background focus after firmare update, findings...

Started Mar 17, 2012 | Discussions thread
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john
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5N background focus after firmare update, findings...
Mar 17, 2012

With the new firmware update to 5N, I thought the background focus problem is solved. No, it’s not.

I did an experiment this morning and found that the background focusing problem with (S-AF) point focus is focusing history (near or far) dependent. If you knew this theory, you don’t need to read further. Otherwise, you will find it very interesting….

I did three different series tests:

1. Deck rail (Near reference), Mulch ground (far reference), leaves (center focus target).

2. Stool (Near reference), house out of window (far reference), leave (center focus target).

3. Grass (Near reference), Woods (far reference), maple branch (center focus target).

The near or far reference objects were picked to be surely focused. Picture names showed the shooting sequence.

The picture below, as an example, showed the test #1 relative positions of the camera and the other objects

Test # 1: Deck rail (Near reference), Mulch ground (far reference), leaves (center focus target). The following pictures showed the leaves focusing results after I shoot a near reference object and a far reference object respectively. (Ignore the picture date, don't know the camera changed my original date setting, maybe caused by the firmware updating)

Far reference: Mulch ground:

Center leaves not focused

Repeat again: Center leaves not focused

Near reference: Deck Rail

Center leaves focused

Repeat again: Center leaves focused

Test #2 Stool (Near reference), house out of window (far reference), leave (center focus target).

Near reference: Stool

Center leave focused

Far reference: House out of window

Center leave not focused

Summary:

1. 5N point focus is not limited to the 'point', it uses a much unknown area to search for focus.

2. 5N back focus problem is not because the background contrast is higher than that of the object. The camera (software or hardware only sony knows) has a focus memory that will search the neighborhood of the previously focused distance to focus on.

3. I tried repeatedly both center point and flex point focus, the conclusions are the same.

4 The work around for this problem is
A: turn on 'peak' to visually confirm your object is focused

B: In case it's not, pre focus to a near object (say ground or closer) by half pressing the shutter release then (you can lift off your finger afterwards) refocus to your object.

PS: I tried C-AF also, and found a additional problem: the focus will not lock anyway, the focus moves back and forth continuously (even I steadily point to a object), regardless what I pointed to.

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Tamron SP 150-600mm F/5-6.3 Di VC USD
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