Rolling shutter causing partial exposure (for strobes)

[Bryce Lansing]

I've heard that the RED didn't suffer from rolling shutter issues as bad as the EX1/EX3, but I have seen some partial exposure problems with strobing lights.

Is this a common problem? Is there any way to avoid it? Any shutter angles or shutter speeds that work better with strobing lights?

 

[Tony Brown]

More likely to be a phasing problem isn't it?

 

[Jeff Kilgroe]

Better to try and time your strobes in accordance with the shutter. Altering shutter speed won't really do anything if the strobes are random and occur during the read/reset period of the CMOS sensor, which is constant.

Split-frame exposures can happen with any high speed event or flash imagery -- muzzle flashes on gunfire, for example. They also can happen with any form of non-global shutter arrangement or mechanical shutter. Split-frame exposures happen with film cameras. The difference between a mechanical film shutter and a "rolling" CMOS shutter is that the mechanical shutter produces a soft out of focus edge and some light bleed across the frame. The CMOS simply just shows an abrupt exposure change with a sharp edge at the scanline it was resetting when the change or strobe occurred.

 

[Joe G.]

Has anyone figured out the best way to fix these in post?

Can you just take the previous frame and the following frame, combine them with a morph program into a brand new replacement; turn up the brightness to simulate the flash, while discarding the bad frame altogether?

Sounds like something I'd try. Are frame blending programs quick and easy and cheap these days?

 

[David Mullen ASC]

Yes, you could discard the bad frame with the flash and put an overexposed frame there instead as a replacement... but then why shoot with a flash at all if those frames won't be used?

You could try keeping the bad frame and at least brightening the non-flash half to blend a little more, reduce the harshness of the transition/split, and hope that's good enough since it's only on a single frame anyway. Since a strobe is so brief, I think the only thing distracting about the half-frame is the fact that the eye sees brightness only on one half, so if you can create an equally bright feeling on the lower half, the half-frame effect may be less annoying.

You could also try old-fashioned flashbulbs and cubes, which have a slow decay time lasting more than a single frame.

 

[Chris Pickle]

I've heard that the RED didn't suffer from rolling shutter issues as bad as the EX1/EX3, but I have seen some partial exposure problems with strobing lights.

Is this a common problem? Is there any way to avoid it? Any shutter angles or shutter speeds that work better with strobing lights?

The Red suffers very badly with rolling shutter.

Listen, I really love the Red and I'm a big fan, and I look forward to the Scarlet. The Red has given my latest project a level of production value that I would not have otherwise attained... but the rolling shutter is horrible. When it's not pure skew from top to bottom of the frame, it is at least a very odd jello effect wobble. I must say it really surprised me.

I suppose I'm in for it now.

Chris

 

[Reinis Traidas]

I just had this issue on set a day ago. We had a strobe light to emulate lightning. At 25 fps it was just a matter of luck timing it. There is literally no way to time it other than just flash it and see if it exposes properly. At 50 fps every flash was either on the top or on the bottom of the frame, but not whole.

Changing the shutter to 360 degrees didn't help either. At 180 and 25 fps some flashes would come up nice, some won't.

 

[Larry McKee]

I shot a project a few months ago where strobes were a big part of the ending scene. We set the strobes to 42 milliseconds to make sure the strobe flash lasted throughout the entire frame. That way, we hedged our bets on when the shutter was open. It seemed to work out fine. Maybe we got lucky.

 

[Tony Brown]

The Red suffers very badly with rolling shutter.

Listen, I really love the Red and I'm a big fan, and I look forward to the Scarlet. The Red has given my latest project a level of production value that I would not have otherwise attained... but the rolling shutter is horrible. When it's not pure skew from top to bottom of the frame, it is at least a very odd jello effect wobble. I must say it really surprised me.

I suppose I'm in for it now.

Chris

Chris do you have an example of this I could view please?

 

[Jeff Kilgroe]

The rolling shutter jell-o effect is an issue sometimes. It is with all CMOS camera systems, just a state of the technology as it currently exists. What were your frame rate and shutter settings? The skew is much more pronounced when using shorter exposure times / faster shutter speeds; The read-reset timing on the sensor is constant, regardless of exposure time.

 

[Ivan Cortazar]

Hello,

Sometime ago I did some testing with a canon speedlight flash and even though it is not the perfect solution with some easy photoshop work I found a work around for strobe photography. Here are my findings and the post I put in Reduser.

http://reduser.net/forum/showthread.php?t=31138

Regarding the Jell-o effect is can be quite annoying sometimes. specially when trying to stabilize some footage.