GH3 GH users - I have a video focus question

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dalemccl

Member
I'm interested in getting a GH4 to replace my Sony HD camcorder. I've been watching the limited number of GH4 YouTube/Vimeo videos, as well as lots of GH3 and Olympus EM-1 videos, to get a better feel for m4/3 video capability. One thing I see somewhat often is that the camera grabs focus, then loses it at some point while shooting, and then quickly refocuses. It may get focus back in a split second or it may take a second or two. It happens for no obvious (to me) reason; the camera isn't panning, and there is limited subject movement. That makes the clip unusable for my purposes. An employee at a local camera shop told me his EM-5 does this too.

My camcorder never loses focus after it locks in, unless of course I pan it to something like a blank wall, but I rarely pan or zoom during shooting. (Most of my shooting is hand-held so there is always a little movement of the camcorder, but not enough to make it lose focus.) I am guessing that the reason I don't see this behavior from the camcorder is that it has a tiny (1/2.88) sensor compared to m4/3, so the massive depth-of-field covers up any momentary re-focusing that the camcorder thinks it needs to do. Does that sound right?

Is this re-focusing issue something that happens often (I'll define "often" as it happens in 1 out of 10 short clips). Or is it more rare than that?

It would be great to replace the camcorder with a GH4 to get 4k video, great stills, and all the other benefits of m4/3, but this has me worried. It remains to be seen whether the DFD focus feature of the GH eliminates this behavior, but I have already seen it occur in one or two GH4 videos on YouTube. Here is one example:

https://www.youtube.com/watch?v=48PvXDBgB_Y

It happens at the very beginning of the video, outdoors in good light; again at 1:17; and again at 2:30 (the last one may have been caused by the guy in the purple shirt waving his arm). This was shot with a pre-production camera, so that could be part of the problem. Most posted GH3 and GH4 videos don't exhibit the problem, but they may not have used clips that did, or they edited out those parts.

Can anyone comment on this? Thanks.
 
DSLR's for video is a different ballgame. Dedicated VIDEO cameras are really made for general video capture purposes with an emphasis on News Gathering and live events.

DSLR's really must be regarded more like FILM cameras because they have some aspects that require more "pre-shot" setup. Auto-focus on all the DSLR's is worse than on good "Video cameras". In fact many good shooters rely entirely on MANUAL focusing.

They'll give BEAUTIFUL results - but not in the same way that video cameras do.
 
Autofocus is generally very limited with DSLR cameras, so you pretty much have to either manually focus your shots or limit the focus range you want to cover. The Canon D70 is probably the best DSLR when it comes to AF, but it has it's own set of problems that are not AF related.
 
TheDingo said:
Autofocus is generally very limited with DSLR cameras, so you pretty much have to either manually focus your shots or limit the focus range you want to cover. The Canon D70 is probably the best DSLR when it comes to AF, but it has it's own set of problems that are not AF related.
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This surprises me, given the popularity of the GH cameras for video and Panasonic's emphasis on giving them top notch video capabilty. I was really hoping the GH4 would work for me. I guess it is as DPStewart said - DSLR cameras require more set up. More suited for controlled filming situations than for the run and gun vacation and family video that I shoot.

But does this problem of momentarily losing AF only happen infrequently? (Maybe I could live with that.) Or is it unrealistic to expect that I could shoot a dozen 10-second clips in a row in fairly low light without it happening (like shooting night time cityscapes of flood lit buildings?

Is the problem related to the larger sensors of DSLR's as compared to consumer camcorders (and thus more shallow depth of field)? Or is there some other technical reason why they can't AF as well as dedicated camcorders?

Thanks.
 
dalemccl said:
This surprises me, given the popularity of the GH cameras for video and Panasonic's emphasis on giving them top notch video capabilty. I was really hoping the GH4 would work for me. I guess it is as DPStewart said - DSLR cameras require more set up. More suited for controlled filming situations than for the run and gun vacation and family video that I shoot.
Thanks.
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Yes, a video camera may be more suited to shooting family video i suppose but not necessarily run n gun. I shoot plenty of run n gun type documentaries and never use autofocus. Broadcast cameras also have no autofocus, it's just a matter if getting used to it.
 
dalemccl said:
Is the problem related to the larger sensors of DSLR's as compared to consumer camcorders (and thus more shallow depth of field) ?
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Dedicated video cameras use smaller sensors, smaller zoom lenses with "deep" DOF, and it's a dedicated non-removable lens that is designed to work with the camera's AF circuitry. A DSLR has none of this.

The GHx series of camera shoot very good video, but the best you can expect for video AF is being able to "touch focus" using the camera's LCD while shooting, which can be very handy sometimes, but the accuracy and speed of focus may not match your expectations.

Because manual focus is such a big deal with large sensor cameras, external monitors and high quality EVFs are necessary production tools when you want to maintain accurate focus throughout your shots. And it's going to be an even bigger deal when shooting 4K because any focusing errors will completely ruin the benefit of high resolution video.
 
When switching from the DVX100 to the GH2, I came to learn very quickly that AF is dead to me. Manual focus only is the way to go (for video at least.)
 
Thanks for all your help everyone. Guess I need to develop manual focus skills if I buy an m43 camera like the GH4.

One other question about this. I don't mind if it takes the AF a second or two to grab initial focus, I just don't want it trying to re-focus during video recording and causing the momentary out-of-focus problem, at least in situations where the subject isn't moving and I am not panning or zooming (which is the case in most of my recordings). So I'm wondering if, in those situations, there is a way to let the AF grab focus before pushing the record button, lock it to that focus point, then push record. A couple possibilities come to my mind.

1. Before recording, frame the shot, let it AF, push the AF Lock button, then start recording. (Or does AF Lock only work when shooting photos?)

2. Before recording, frame the shot, let it AF, switch to manual focus, then start recording.

Would either of these work to lock focus during recording?
 
You can put it in AFS mode, which focues the shot once on a half press of the standard shutter, and leaves it there. AFC (auto focus continuous) is the one that will hunt.
 
Jim Simon said:
You can put it in AFS mode, which focues the shot once on a half press of the standard shutter, and leaves it there. AFC (auto focus continuous) is the one that will hunt.
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Thanks Jim. I didn't realize that you can half press the shutter button, then press the movie button to start video recording. That's great news.
 
While everyone is giving the big thumbs down, I will add this caveat. It can work in the right situations, but it takes practice, and the right situation. I have the gh2 and I often use the multi point AF and direct it where I want the focus to be. Right or left or top or bottom of the screen. This is really the key for me. I do have to often work to tell the AF the general location to look at, and from there it usually does a pretty good job. If you just let it have free reign though, and you have shallower depth of field with detail going on in the background, it may have a tendency to hunt. Also, some lenses are much better than others. The 20mm 1.7 is nearly useless for AF for video, but my 14-140 is the one I use most often with AF.

I will say that I absolutely do not consider AF to be useless. It has it's uses in my workflow for sure, but it's not at the level of a designated video camera.
 
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blazer003 said:
While everyone is giving the big thumbs down, I will add this caveat. It can work in the right situations, but it takes practice, and the right situation. I have the gh2 and I often use the multi point AF and direct it where I want the focus to be. Right or left or top or bottom of the screen. This is really the key for me. I do have to often work to tell the AF the general location to look at, and from there it usually does a pretty good job. If you just let it have free reign though, and you have shallower depth of field with detail going on in the background, it may have a tendency to hunt. Also, some lenses are much better than others. The 20mm 1.7 is nearly useless for AF for video, but my 14-140 is the one I use most often with AF.

I will say that I absolutely do not consider AF to be useless. It has it's uses in my workflow for sure, but it's not at the level of a designated video camera.
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Thanks, that's encouraging. I think I am going to rent a GH3 and a couple lenses to get a good feel for how often the AF loses focus and has to regain it during video shooting. One of the lenses I'll rent is the 14-140 that you use. I'll probably rent the 12-35 f2.8 also. That will help me decide whether m43 will work for my needs or whether I should stick with camcorders.
 
I have considered this option as well

What you need is a par-focal lens which what they use on most camcorders. Once focus is set on a par focal lens, everything will remain in focus throughout the entire focal range
 
True North said:
I have considered this option as well

What you need is a par-focal lens which what they use on most camcorders. Once focus is set on a par focal lens, everything will remain in focus throughout the entire focal range
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From what I understand, the Panasonic micro four-thirds lenses aren't par-focal; only lenses designed specifically for film/video are. Is that right?

I rarely zoom (or pan for that matter) during shooting so I am not sure if par-focal would help anyway since the focal length would be constant during shooting. What I would like to avoid, or at least minimize, is when the auto-focus initially achieves focus but then loses it sometime during shooting a clip and has to refocus. I understand the need to refocus when the subject is moving, or the camera is panning, but I often see videos where the camera loses focus for no apparent reason, so it results in a brief out-of-focus moment sometime during the clip.
 
dalemccl said:
I understand the need to refocus when the subject is moving, or the camera is panning, but I often see videos where the camera loses focus for no apparent reason, so it results in a brief out-of-focus moment sometime during the clip.
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Unless a clip length is absolutely needed, focused or not, that is just bad editing. But I do find that the Panasonic 14-45mm on my GH2 will annoyingly refocus at times, especially if there is a busy background (and I've had to use the clip due to length). Philip Bloom just did a piece on the Canon C100 software upgrade that allows auto focus and there is some pertinent information in there. I've yet to figure out how to avoid the issue and I'm hoping that the GH4 will address some of that (hope is all it is at the moment).

I'd even consider his solution if I could get it to work on the GH2.
 
Well there's also the option of going to the 70D if you want an option that gives big-sensor beautiful images AND incredible autofocus (you touch it and it goes there, no hunting, no playing around, does a better job than a focus puller!)
And if moire and aliasing are a deal breaker for you, Canon are introducing a 7D mk II around NAB, will have a very sharp image and also the Dual Pixel autofocus implementation. The GH4 is awesome, but I would say it's a manual focus camera for video. Learning the skill is beneficial though more than having the camera (70D/7D) do it for you! :D
 
Canon 70D has the best AF system right now. Its better than the C100 because it is giving options as to where you ll put the focus point (on C100 its only center of frame), it has usable face detection and it works perfectly with the touch screen.
Is it comparable with camcorders? I have an XF100 right now and my past camcorders were DVX100B and HMC150. I can say that its MUCH better! BUT you have to learn how it is working, how to use it and most importantly where NOT to use it!
Its really amazing to be able to shoot in minimum lighting at f1.8 and be confident that your shots are in focus!
 
Ebrahim Saadawi said:
Well there's also the option of going to the 70D if you want an option that gives big-sensor beautiful images AND incredible autofocus (you touch it and it goes there, no hunting, no playing around, does a better job than a focus puller!)
And if moire and aliasing are a deal breaker for you, Canon are introducing a 7D mk II around NAB, will have a very sharp image and also the Dual Pixel autofocus implementation. The GH4 is awesome, but I would say it's a manual focus camera for video. Learning the skill is beneficial though more than having the camera (70D/7D) do it for you! :D
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Thanks for the suggestion. I want to keep the camera and lens size small, which is why I am interested in micro four thirds rather than regular DSLRs. Developing the skill to manually focus quickly and accuracy sounds like a challenge. Maybe it is easier on micro four thirds cameras than with my small Sony RX100. With that camera, even with using peaking, I find that I can't manually focus as well as the auto-focus.
 
[/QUOTE] Learning the skill is beneficial though more than having the camera (70D/7D) do it for you! :D [/QUOTE]

Totally agree about learning the skill...but if the camera can make my life easier...I will just say THANKS:)
As Mr Bloom said...its just another tool!
 
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