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Occasional Contributor
Posts: 6
Registered: ‎12-12-2019

EOS 750D Movie Mode random auto focus adjustment

Howdy,

 

I have a 750D with Tamron SP 24-70mm lens

 

While shooting video, the camera suddenly re-focuses creating a white out or a black out for 1/2 second

 

Here are two examples of problem.

https://youtu.be/_ilV-dM5x6w

https://youtu.be/ISYRZ8teky0

 

I have tried a range of solutions - turned off auto-focus on camera and lens, set white balance to indoor, reset the camera. 

 

It does not matter what location or light settings I am in, this keeps happening

 

Can anyone please tell me what causes this and how to fix it

Thank you 

Esteemed Contributor
Posts: 4,685
Registered: ‎02-17-2016

Re: EOS 750D Movie Mode random auto focus adjustment

Do you have a canon lens you can try?

 

Have you had any issues with the shutter button? This should only happen when the button is pressed half way.

Occasional Contributor
Posts: 6
Registered: ‎12-12-2019

Re: EOS 750D Movie Mode random auto focus adjustment

Thanks for the reply KV,

 

Unfortunately I dont have another lens to try. I will see if I can borrow one from somewhere and try that.

 

Ive had no issues with the shutter button.

VIP
Posts: 11,546
Registered: ‎08-13-2015

Re: EOS 750D Movie Mode random auto focus adjustment

What shooting mode are you using? Test in Manual.
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"Doctor told me to get out and walk, so I bought a Canon."
Occasional Contributor
Posts: 6
Registered: ‎12-12-2019

Re: EOS 750D Movie Mode random auto focus adjustment

Thanks for the reply Wadizzle,

 

yes, set up in manual. Following this set up - https://youtu.be/fYVHbBkArJA

VIP
Posts: 11,546
Registered: ‎08-13-2015

Re: EOS 750D Movie Mode random auto focus adjustment

I suspect that you might be seeing the effects of light flicker.  Test it with different lighting types, like outdoors on a sunny day.

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"Doctor told me to get out and walk, so I bought a Canon."
Esteemed Contributor
Posts: 4,685
Registered: ‎02-17-2016

Re: EOS 750D Movie Mode random auto focus adjustment

Which raises the question, is it the mirror flipping up that causes the black-out? Do you hear it? That is the assumption I have been working on.

Reputable Contributor
Posts: 704
Registered: ‎02-13-2016

Re: EOS 750D Movie Mode random auto focus adjustment


@Waddizzle wrote:

I suspect that you might be seeing the effects of light flicker.  Test it with different lighting types, like outdoors on a sunny day.


If it were light flicker related, wouldn't it happen at fairly regular intervals? Like every 10 1/2 seconds or every 2 minutes and so many seconds? I wonder if changing the frame rate would have any effect, or verify or eliminate the problem?

 

It almost looks like the on camera flash is sending out a short focus-assist flash. But I doubt the camera would do this in video mode, or that he even has the flash popped up and powered on. The lighting is pretty challenging in the second video but I don't see that as a reason for this kind of behavior from the camera.

 

In some ways it looks like a flash of light but then it also seems like the sensor acting up and affecting the whole screen. And that also doesn't explain the sensor "blacking-out" on occasion.

Occasional Contributor
Posts: 6
Registered: ‎12-12-2019

Re: EOS 750D Movie Mode random auto focus adjustment

Thanks for the thoughts BurnUnit.

 

The problem does not occur at consistent time intervals. I have looked at different ways of triggering the "adjustment". I have filmed in different light (indoor and outdoors), and under different lighting conditions (natural light and studio). I have filmed static objects and dynamic (me) and there is no pattern to the "adjusment" occuring.

 

I changed the frame rates as you suggested as well as changing the image quality and the problem still occurs.

 

I am using a ScanDisk Extreme SD card (90mbs - Class 10) which should be sufficient for capturing data 

 

The flash has not popped up.

 

I am trying to track down a basic canon lens to see what happens 

Esteemed Contributor
Posts: 4,685
Registered: ‎02-17-2016

Re: EOS 750D Movie Mode random auto focus adjustment

So, does the mirror actually flip?

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