JVC manual focus & flicker problem
 

I wanted some more opinions about a problem I am having on my JVC GY-HM170, I have new footage I shot with three of these cameras on this shoot. I took care to manual focus and lower the exposure to control flickering of the brights in the background.

As you can see in this test footage I had multiple problems on two cameras. Listen to the description and see if you ever had anything like this. What could be causing this?

Re: JVC manual focus & flicker problem
 

To me it looks like the camera is hunting for focus which should not be the case if you say you where in manual focus. My guess is that there is a setting in the menu that still allows for the camera to refocus in manual mode.

Re: JVC manual focus & flicker problem
 

Firstly, I'd suggest resetting the camera.

I know nothing about your model, but you need to check that it's in a standard video mode, stabilisation is off, AF and any wide latitude options are switched off too.

I wouldn't call the problems you are seeing 'flicker', more like an image processing error on high contrast areas. That's why you should try to discount any processing tricks that might be turned on in the camera.

Re: JVC manual focus & flicker problem
 

Thanks, I had the cameras check out at JVC in Long Beach CA. They reported no problems with the computer specs and they could not duplicate the problem (although they tried them outside in even daylight, not high contrast.

When I get the cameras back I will try to find out what I am doing wrong however the cameras were reset to factory original specs, I turned off Wide Dynamic Range (which helped), detail (however the image is fuzzy), and kept the exposure down. Still the brights flicker.

I will keep this thread updated.

Re: JVC manual focus & flicker problem
 

Update: JVC repair facility has gone over the cameras and found them to be within computer and scope specs. They could not duplicate the problem in their field test.

I took the first camera out of the box put my stripe shirt on the chair and again was able to duplicate the problem. Is this the way the cameras are to work? Can anyone duplicate this effect? All you have to do is make sure part of the object is overexposed, does not matter if your manual focus, shutter speed, detail, wide dynamic range set.

Is this common effect on JVC GY-HM 170u cameras?

Re: JVC manual focus & flicker problem
 

UPDATE:
JVC was good enough to have my cameras returned to Long Beach for further investigation, however; the opinion came back that this was all operator error. In particular, the flickering was called MOIRE, I disagree because of this video.

Here in this video, there are no lines or stripes to affect the Bayer CMOS sensors of the camera. By the way, Canon Support just told me they have anti-aliasing filters on their Bayer sensors with the Canon XF-100 I had returned. I never had this problem with the Canon Cameras.

There are two clips here one is at the beginning where we see flickering on the pink shirt and one at 00:55 where the same camera, play, shirt, does not have flickering.


What do you think this is if it's not moire?

Re: JVC manual focus & flicker problem
 

Operator error?? So jvc thinks it's your fault that the camera is not able to resolve the fine detail?
It could be moire but the camera displays it in the way that I have not seen before, especially the flashing that is very obvious.

Re: JVC manual focus & flicker problem
 

I talked to a former engineer representative of JVC and he feels the camera's sensor for 4k is being pushed. He suggested shooting lower on the iris then you normally would so that the camera is not overworked. Skin tones should be at 50% rather than the normal 70%.

I agree since shooting darker seem to avoid the flicker problem.

Re: JVC manual focus & flicker problem
 

That was some very strange stuff happening on his pink shirt. At least that's all I could see in the Vimeo file. Can you reproduce this artifact in controlled circumstances with professional video lights? There seems to be a few possibilities that are promoting this effect.

One: That area on his shirt is overexposed. Nothing much you can do about it, the faces are properly exposed and I assume that you are not in control of the stage lighting during the performance. Does this happen when exposure is optimal for the area? Can you change the knee settings on your camera? This might be an effect when the camera is trying to squash the overexposed area.

Two: Do you know if that particular stage was using multi-color LEDs? I filmed this summer at a place that just installed some very intense multi-color LED background stage lights replacing the old style wash lights I had filmed with before without a problem. I can tell you that whenever the lighting went to intense blue, my camera (a JVC HM600) at a 60th shutter recorded a distinct flicker that was barely noticeable to the audience. All the other colors were fine on camera. Not saying that this is your problem, just an experience I recently had.

Three: Is this moire effect visible when you connect the camera directly to a monitor? Does it go away if you change the sharpness settings in the camera? Does it happen with all shutter settings?

Re: JVC manual focus & flicker problem
 

I didn't watch the video but it's a well know fact that fine strips found on shirts can cause moire problems and some cameras are more susceptible. That's why you don't see newscasters wearing them. Video cameras also have difficulty with red.

Re: JVC manual focus & flicker problem
 

"It's a well know fact that fine strips found on shirts can cause moire problems and some cameras are more susceptible."
True but this is a plain pink shirt.

Re: JVC manual focus & flicker problem
 

If you don't watch it you don't know what the problem is :) This has been reported here before but couldn't find the video back but it had the same issue, it looked like a combination of overexposure and moire, it resulted in flashing overexposed areas when the camera moved a bit, nothing like "normal" moire" I have seen before.

Re: JVC manual focus & flicker problem
 

Can you reproduce this artifact in controlled circumstances with professional video lights?

Yes, you can see more video here, especially the rather plain chair that is flickering.
http://www.dvinfo.net/forum/jvc-4k-p...r-problem.html

“Does this happen when exposure is optimal for the area?”
Yes and No, if everything is dark then it works better, if you have some chrome or bright reflections off metal there is flickering. C stands, drum sets, mic stands.

“particular stage was using multi-color LEDs”

Perhaps not that stage but I have had shoots with those lights before the firmware was updated in the cameras and I did have loads of problems. These cameras are better with the latest updates.

“moire effect visible when you connect the camera directly to a monitor?”

Yes, I can see it on a monitor. Yes if you take all the detail off or turn it down it will go away but your image is blurry. Yes, different shutter settings and it will still happen depending on how bright or dark the image is.

Re: JVC manual focus & flicker problem
 

JVC is also looking at two other problems (also camera operator error according to the initial response)

1. Ghosting of background and foreground.

2. Focus lose on zooming or panning.

You can see some examples here:

Re: JVC manual focus & flicker problem
 

I'm browsing on my phone and it doesn't support the video.

To put it simply if you can't change your environment then you need to adjust your camera. There are camera settings people have suggested to reduce moire ie reduce sharpening and change the frame rate, change the resolution. Your response has been yeah but I don't want to... I'm not sure what else there is to say.

I recently posted a video where stage led lights were causing a strobbing effect . Seems these issues are cropping up more often.

Re: JVC manual focus & flicker problem
 

I agree with you there are things that can be done for cinematography, paid interviews, info commercials shots but my world is live, no dress rehearsal, walk in and the action happens. I depend on crews to make the needed changes but even the former JVC engineer today told me it's hard to get TV crews to change off of auto.

Regarding resolution, If I start the event in 4k I can not stop to change cameras setting. We're going to the end of the show with what we started. Beside tests show it happens on 1080p just like 4k, no difference. Likewise, I can not start in 1080p and then realize I could have had enough light to shoot in 4k.

Regarding sharpening; I don't want my images blurry, it has to go to -10 which is too much blur.

Regarding frame rate; in weddings, stage plays, concerts with lighting. I am at 24 fps and 24 shutter with 12 DB gasping for more lux. These cameras do not do well in low light. I always shoot 30 fps with 60 shutter if I have the light.

If you could I would really like to see your video of the led lights were causing a strobbing effect.

And thanks for your interest and comments on my problem, I do need the help right now.

Re: JVC manual focus & flicker problem
 

Now that I know what your doing with the shutter I doubt it's the resolution. Btw low shutter will also contribute to softness. 24 @ 24 shutter is a serious no no.
I do low light events too but at some point it is what it is. There are consequences when you depart from standard practices.

Here's the video
http://www.dvinfo.net/forum/panasoni...low-light.html

Re: JVC manual focus & flicker problem
 

There are two things that I agree with you is wrong with the camera:

1) That strange moire on the pink shirt. That is not normal for even cheaper cameras.
2) The image lag as you shake the camera in the restaurant. I would expect that in a very cheap camera or smartphone. Even with a slow shutter it shouldn't lag like that. Something is wrong with the camera's processors.

The other things in your video are different issues.

The focus shift is either from the camera not really being focus in the wide shot and the auto-focus is hunting now that the image has changed or there is damage to the zoom. I had a camera that came that way and it was exchanged when JVC saw that it was clearly damaged in shipping. If you use manual focus and it goes out of focus when you zoom in and out after you set your focus zoomed all the way in, then you have a damaged zoom. By the way, DSLR zoom lenses don't hold their focus when you zoom in and out. Video zooms should.

The glitch you circled in the outdoor footage is an insect flying by.

Re: JVC manual focus & flicker problem
 

Thank you for that detail, that is the best advice to answer these concerns. I found out today that when JVC sent the letter blaming camera operator they also sent the cameras back. They are not going to look at the problems. Thanks to your insights I can do more investigation and ask better questions to JVC support.

When you say, "camera not really being focus in the wide shot", you do realize that the camera is on auto focus and given the depth of field the talent should be in focus on the wide shot. With the moving around on the stage, I depend on the camera to grab a focus on a wide shot. I have other examples of focus lose. Here are some slow zooms with auto during interviews. I did not expect the camera to act this way.

Re: JVC manual focus & flicker problem
 

OK. That looks exactly like a back focus problem.

Please shoot a test video in daylight, on a tripod.
Use manual everything!
Do not use a wide open iris.

Zoom in all the way to a distant object and manually focus on it.
Now zoom out.
Is it still in focus?

Now zoom out and focus on an object in the middle distance.
Zoom in.
Is the focus shifting to the foreground or background?

Re: JVC manual focus & flicker problem
 

That's not a backfocus problem if you ask me, just the autofocus that gets confused. Maybe the lens is also not designed to keep focus when you zoom in, lock focus and zoom out.

Re: JVC manual focus & flicker problem
 

I expect that this camera doesn't allow the operator to manually rack focus and while zooming at the same time. Can you please confirm this Ronald?

Like most built in lenses I doubt it's parfocal, so the electronic will automatically adjust the focus as you zoom to accommodate the expected focus shifts.

I reckon the back focus is off and when he zooms the electronics are incorrectly adjusting the focus to compensate. Then once the zooming stops the camera turns on autofocus again and focusses it properly.

It's the same repeating pattern on every zoom. If the camera was simply struggling to find focus then it would do it all the time regardless of the zooming. But it happens just after the zooming starts.

The best way to check is to do a zoom with the focus in manual and see what happens.

Re: JVC manual focus & flicker problem
 

Sorry you're having these problems Ronald. I bought a pair of the HM-170s about three weeks ago. Our cameras do have some limitations.

Though I've only used the two new cameras on two jobs so far, the only problem I've run into as yet was due to "muscle memory" from my two previous cameras the JVCs are replacing (Canon XH-A1S and older XH-A1).

With a camera like the HM-170, I don't think using auto focus is EVER a good idea. That one problem I experienced was when the camera somehow accidently slipped into auto focus instead of manual focus on me, and that was probably due to an old habit I had with my Canons. They had a great instant autofocus with a handy button for it on the side in the exact same place the side where the two AF/MF and FULL AUTO buttons are on the JVCs. I'm certain I pushed one of those buttons reflexively. Then there was that dreadful auto focus hunting... like in your short video of the interviews above. Exactly like that. MY operator error.

The JVCs don't have the great autofocus my two Canons did. I don't expect them to. The Canons were expensive when new. The JVCs are very inexpensive. But they are still a good value for me, as long as I use them within their limitations.

I'm still getting used to my two new HM-170s. To help, I bought a varizoom controller and an external monitor. They really help with nailing the manual focus. The peaking also helps, but I don't use it when I have the external monitor hooked up. It's not necessary. You can also turn on the settings for the camera to display the focus distance info. When you set it so the Infinity symbol is showing (looks like a sidewise "8"), everything farther from the camera than the minimum focus distance is in focus. That's a trick I've used on other cameras when filming performances or sports to keep people from moving in and out of focus. I'd used the Canons for years on hundreds of jobs, so didn't need the monitor for them, because I knew the cameras so well. I knew when I could trust focus and when I could not.

The color problems are a different issue. That pink shirt and stage lights might be tough to deal with on various cameras if that was a very saturated pink. Could be the single, relatively small chip running up against it's limitations. I filmed a concert with my Nikon DSLR and stage lighting and clothing with saturated colors caused some problems. I cut to one of my 3 chip Canons then when editing.

Sorry, I'm not surprised JVC service found nothing out of the ordinary. There are trade-offs to consider between different cameras. If most of my paying work was stage performances under varying lighting conditions, I would have chosen a different camera. For my corporate and legal work, the JVCs are fine.

Re: JVC manual focus & flicker problem
 

Roger, a few questions.

Can you zoom and pull focus at the same time on this camera?
Does it have autofocus override so you can tweak the focus while in autofocus?

I owned a few DV cameras where the electronic lens' focus correction would stop you from adjusting focus while zooming.

Re: JVC manual focus & flicker problem
 

Roger made good points different cameras excel at certain applications. With in reason there is some degree of cross over between applications. For low light, shallow dof and auto focus you can't beat dslr and mirrorless cameras.

HM-170 is an odd mix. A single 1/3" sensor isn't good for low light especially in 4k. It's surprising it does 4:2:2 in hd but that would be my format of choice. Although it makes me wonder how its fitting 4:2:2 @50 bit rate. I'd wager the small sensor and compression most likely negates the benefits you would expect in 4:2:2 as seen in the pink shirt which I add is also over exposed. Stage light and color is challenging don't over expose and be happy with what you have.

I once used this camera for a rock band shoot and was blown away by the quality for such a tiny inexpensive camera. But that was under non stage lighting with little or no gain.

This camera isn't for low light concerts or rack focus shots and shallow dof interviews. I get under a limited budget you use what you can afford but it seems to be more like you're exceeding the limitations of the camera.

I finally looked at your videos and stand by everything I said before seeing them about the moire and the pink shirt. I grant you the camera has some oddities but there isn't anything defective.

Re: JVC manual focus & flicker problem
 

Tha footage is worrisome as the camera should at least be catching the focus in the center of the frame. Why the camera had a bit of restaurant booth to the left in focus and not the people or the center is baffling to me. Does your camera have a focus zone option? On my Panasonic GH camera, using the LED screen, you can decide where in the frame the auto-focus should focus which is great for tripod filing but terrible for handheld. I almost never used it. You should really test the zoom the way we have described. The broken HM600 zoom I returned had similar focus problems as your zoom is showing in this clip.

Auto focus is not reliable with very wide shots, especially in dark rooms with the subjects not taking up a significant portion of the frame. Shooting theatrical productions I have used DSLR cameras that will be in focus and suddenly decide the background 15 feet behind should be the focus point. Even with "face detection" enabled. The interviews you just posted can be focused manually, there's no reason to use the autofocus in a stable situation like that.