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captain3d

Sony A6400 focus popping on long video takes

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Hi  All

I have been using an A6400 and 16 - 50 kit lens for a few months to shoot a series of whisky tastings at a table. The camera is static on a tripod. I sit behind a table. lighting is bounced. Very simple.

In recent weeks the focus has started to pop/pulse. On long takes (30 mins +) it goes from slight popping to over the top unwatchable pulses of bad focus. The focus is set to continuous and limited to a central upper zone. Face detection is off. I suspect it is related to the camera heating up. After letting the camera cool down the popping was reduced but not completely gone. I believe the problem is getting worse the more I use the camera. I have shot approx 30 hours of video in this setup. The last five are showing the problem.

Here is a link to an example of the problem. 

https://youtu.be/Kz_qi1y5puk

Anyone else seen this issue? Faulty camera? Faulty Lense? Or A6400 issue? What to do?

I ran a three hour test tonight with manual focus and everything looked sharp and stable so must be a fault with the auto focus. I will try other modes tomorrow.

phil

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I did another continuous auto focus test today using an external power supply plugged into mains and things look good. I am now testing to see if it is battery power sagging as it gets low that is causing the issue. Maybe third party battery issue?

Will report back. If I can confirm.

phil

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Nope it was a mechanical and possibly heat related thing. I had a long aluminum bar for a small boom mic clamped between the tripod and the camera base. Small movements would cause the mic to bounce very slightly and this was somehow causing the focus issue. 

The bar must have been slightly flexing the camera? Took a while to find out the cause.

 

phil

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Yeah took three days of testing to track it down. It did seem to get worse as the camera warmed up. I confirmed it was not electrical by unplugging the mic and the big lights. It was not visual as I lifted the mic boom well clear of the FOV of the lens. Removing the mic boom solved it.

I am 99% sure some mechanical pressure was causing an electronic issue inside once the camera was warm. Stepping through the frames you can see the blur across half of the image (1/60th shutter speed) where the rolling shutter captures the change. So the focus as changing very rapidly. Nothing was touching the lens.

At least I can get back to shooting. See pic below of the problem setup

phil

Screen Shot 2019-05-17 at 5.54.04 PM.jpg

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