GH4 Advice needed on stuttering vision

C

Craig in Oz

New member
Hi folks,

I need some advice.

I recently shot a courtroom on my GH4. I needed a long roll (90 minutes plus) so I used the Panasonic 64gb card and set the camera to:

FHD 50 MBS

1920 x 1080 - 25p

Shutter speed 1/50

This is the problem. At the start, using mostly available light, everything looks fine. When people move in the frame it looks normal. But then we turned on 2 x 1k lights (Tungsten) and things got weird. The vision becomes quite stuttering and people blur when they walk through frame.

Heres the vision : https://vimeo.com/129171312

I'm a bit baffled. My initial thought is that 50 mbps may have been too low a rate to allow the camera to write all the info, but I have no scientific basis for believing that. Otherwise, I'm at a loss to know what I did wrong to get that result.

Any advice is much appreciated!

Craig

(Melbourne, Australia)
 
Yeah, that looks like shutter speed changed somehow. Make sure you are on manual settings, EXPOSURE MODE M in the menu.
 
Larry McKee said:
Kinda looks like your frame rate changed to 10 or 12 FPS.
Click to expand...

Barry Green has previously pointed out that the GH cameras have a serious glitch where it's possible to set a shutter speed that's slower than the (reciprocal of the) frame rate, which (if I recall correctly) forces the the camera to shoot at a lower frame rate.

A simple way to avoid this glitch with the GH4 is to use shutter angles instead of shutter speeds.
 
I wouldn't call it a "glitch" per se, it's just that you cannot have a frame rate that's faster than your shutter speed. If your shutter speed is at 1/24, then your frame rate cannot possibly be 30 fps. If your shutter speed is 1/50, you cannot have a frame rate of 60 fps. The camera will hold and buffer the frame to complete the exposure, and if you're shooting at 1/12 shutter (even if you set the camera to 60p), the most distinct frames you can possibly expect would be 12 frames per second. If the camera records 60p in that instance, it'll record duplicated frames, so 12 frames, each duplicated four times, so there'd be 5 copies of every frame.

The OP said that they had 25p and a 1/50 shutter speed, which should have been just fine. The problem would be if they were shooting 50p with a 1/25 shutter speed.

But I do agree as others suspect, the shutter speed certainly looks like it was changed somehow.
 
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