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Autofocus in Video mode

giuliocanale

By giuliocanale
in Fuji X-T2 / Fuji X-T20

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giuliocanale Rookie

giuliocanale

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I have a XT-2 with 18-55.

When I record a video in AF-C the camera often refocus in and out. The same problem also with 35 f2.

The problem is more visible if your subject is not moving. For example, if I record a fix subject in AF-C the camera continues to focus in and out (really small corrections).

 

Please let me know if someone has the same problem.

 

Many thanks,

Regards.

Giulio  

 

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Adam Woodhouse Proficient

Adam Woodhouse

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That is a quirk of the Fuji cameras.  Was worse on XT1 but they released a firmware several months back that helped to reduce it.

 

Your best bet is to leave the camera in AF-S  and lock focus then start recording. The camera will not change focus again while video is recording.  That's the best route.  Or go manual focus and press the AF-L button to engage the autofocus .. then start your video recording. The results are the same either technique.

 

The AF-C is best for when your subject or camera are moving.

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giuliocanale Rookie

giuliocanale

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Adam,

thank you for your reply. I have understood that it's a common fault so that my xt-2 doesn't need assistance: I was worried that something wrong was in my camera.

I hope Fuji will solve the problem soon because otherwise it's not possible to use AF-C. For that reason I'm using manual focus in order to change it while I'm recording.

 

The strange thing is that I have seen many autofocus video test in you tube and nobody underlines the problem. Maybe one/two video are affected from the problem, the others seem ok and they're recording in AF-C.

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Adam Woodhouse Proficient

Adam Woodhouse

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Maybe there are ways to get AF-C to hold focus and not continually do micro adjustments to the focus while you record.  Maybe some people find single point AF-C works better than multi-point AF-C?  Or maybe they have face detection on while in AF-C?  I haven't yet played around with those different settings when shooting video.

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kimcarsons Collaborator

kimcarsons

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This behavior sucks. It would help if there were an 'AF sensitivity' setting for video that would allow the user to make it less aggressive at hunting. How much it does hunt depend on the lens and the lighting (and the aperture!). You definitely want to make sure the firmware is up to date on all your lenses. 

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giuliocanale Rookie

giuliocanale

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This behavior sucks. It would help if there were an 'AF sensitivity' setting for video that would allow the user to make it less aggressive at hunting. How much it does hunt depend on the lens and the lighting (and the aperture!). You definitely want to make sure the firmware is up to date on all your lenses. 

 

 

I agree with you: at the moment, for me, it is not possible to use AF-C.

I have done many test and I didn't find the solution: the problem remains.

At the moment, in video setting, you can use just single point (not multi point and not face detection).

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kimcarsons Collaborator

kimcarsons

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I agree with you: at the moment, for me, it is not possible to use AF-C.

I have done many test and I didn't find the solution: the problem remains.

At the moment, in video setting, you can use just single point (not multi point and not face detection).

 

It's kind of a catch-22 with the aperture. A smaller aperture gives you more depth of field, so the pumping is less noticeable, but a smaller aperture also makes the camera switch from phase to contrast detection AF, which inherently hunts more. I think the face detection mode is always using contrast AF (when it's locked on to a face anyway) (I've heard that the Sony implementation of face AF is able to operate with phase detection, but it seems that Fuji hasn't figured out how to do that yet). When using an aperture wider than f/5.6 and not using face detection, the AF-C in video isn't too bad. 

 

Another complicating factor is that some of the lenses (e.g. the 35mm/F2) have focus breathing which makes the pumping of the autofocus much more noticeable/distracting.

Edited by kimcarsons
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Adam Woodhouse Proficient

Adam Woodhouse

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I agree.  I think a bit more work may be required to fine tune the autofocus capabilities of the camera when in video mode.  There is a known glitch when recording 4K and having the camera in manual focus (camera will randomly re-focus) ... maybe a few more tweaks will get done at the same time.  :)

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JEH Newbie

JEH

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Well I was about to send my X-T2 back to Fuji to have this fault fixed. I have been chatting with Fuji UK support dept and they never mentioned that this was a known problem - they suggested sending it back for repair. To be clear, if I start shooting 1080p on a static scene, it's fine for about 45 seconds after which the focus will become unstable and start hunting around. Is this really normal? I also find the exposure will jump up and down ⅓ stop or more.

 

Adam you say this is a known glitch - known by whom and where might I read about this?

 

Since I only have a few days before going on holiday, what's the workaround?

 

Thanks.

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JEH Newbie

JEH

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I have a XT-2 with 18-55.

When I record a video in AF-C the camera often refocus in and out. The same problem also with 35 f2.

The problem is more visible if your subject is not moving. For example, if I record a fix subject in AF-C the camera continues to focus in and out (really small corrections).

 

Please let me know if someone has the same problem.

 

Many thanks,

Regards.

Giulio  

 

As you say Giulio the problem is most noticeable for me when the scene is static. Have you also found that the exposure jumps around - I get this even with a manual lens attached. Doesn't this issue make the X-T2 nigh on useless for video blogging - and why hasn't more been said about it? Is nobody using their camera X-T2 for video?

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Adam Woodhouse Proficient

Adam Woodhouse

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Hi.  The glitch I was referring to was a YouTube video I watched a couple months back where a couple of fellows were doing a review of the Fuji system and used the XT2 to record the video ... but had it in 4K.  They used manual focus for the recording but the focus would actually adjust every now-and-then where the recording would go in and out of focus.  That should obviously not happen when in manual focus mode.  They commented in the video (I think it was by putting a text overlay when they uploaded it) that they didn't know (and was surprised) the focus was doing that and that they reported it to Fuji and said Fuji was aware of the glitch.  They also commented in 1080p it doesn't do that (while in manual focus).

 

When it comes to recording 1080p ... I have put my XT2 on a tripod and recorded speeches at weddings.  Manual exposure and manual focus.  The longest was a speech that went 25 minutes.  I have not had any automated and unwanted focus changes or exposure changes as of yet.

 

I did do a video for a real estate agent recently, and in one of the short video snippets of the property, the video did something odd.  It was a quick in and out of focus (when it shouldn't as I was using AF-S and locked my focus point before I started recording).  But it only happened in one short scene.

 

I have noticed that if the EVF is set to auto exposure but you are recording video on manual settings, the video will maintain its consistent exposure as you move around however what I see on the LCD/EVF will change since it is in auto exposure.  That throws me off as I think the video is also changing ... which it is not.  If I set the EVF to be manual preview (which I now do all the time for video) I have found that works best when shooting manual video.  

 

When you say exposure will jump around, is that what you see while you are recording, or you see it in the results?

Edited by Adam Woodhouse
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JEH Newbie

JEH

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Re-reading your comment and the last one, it sounds like that glitch with 4K was something different. 

I wasn't using the EVF but the brightness jumps on screen and is as recorded. I tried using a manual lens to rule out problems with auto aperture and got the same issue. I'll hopefully be able to post a link to an example which was trimmed off the end of about 1minute of recording. Up until 40seconds in, it was rock steady, then this:  

http://jumpingspider.co.uk/fuji-pentax-lens.mov

 

Wow that was a long wedding speech!

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