Bizarre Green Light Problem

[johnsalomon]

Hi there,

I've been running into something very odd recently. I take a lot of medium exposure (~30sec) shots in very low light conditions, and walk around bouncing a flash off the walls and behind the camera.

A lot of these pictures have a green tint along the bottom. It is driving me up a wall - does anyone have any ideas? Could this be a sensor fault? It only happens with long exposures when I set off multiple flashes; leaving the shutter open without the flash doesn't cause this. It is always the bottom long edge.

Camera is a 5DMarkII, and I only get this with a 24-105mm f/4 lens. I occasionally use a UV filter to protect the lens from dust, but I can't imagine that it'd be some sort of refraction (because then it wouldn't just be at the bottom long edge.) Another possibility is some sort of weird viewfinder light leak, but I don't shine anything directly through it, although I sometimes set off a flash or two behind the camera.

Any help would be very welcome, as this is driving me nuts.

Here are some examples:





And here is a comparison long exposure without the flash:

[scootermcq]

Looks like it relates to shutter curtain, but it baffles me as to what it could be. Just to get the juices going, how many actuations on the shutter?

Also, have you tried different shutter speeds while using flash? Could it relate to a sync speed and some sort of crazy refraction off the rear shutter?

[zenandzen]

I would mask off the viewfinder and take some test shots.

[scootermcq]

Originally Posted by zenandzen

I would mask off the viewfinder and take some test shots.

Good thinking.... I would also try masking the distance scale as well. I have heard of light leaking in on one other lens as well.

[zenandzen]

Just had another thought ...

maybe there is a very slight light leak from the LCD backlighting into the camera body and it will only show up on long exposures.

[oldwolf]

How are you bouncing the flash and what color are your clothes? If the clothes are green and any light from the flash hits your clothes then you'll get a green bounce.

[scootermcq]

Originally Posted by oldwolf

How are you bouncing the flash and what color are your clothes? If the clothes are green and any light from the flash hits your clothes then you'll get a green bounce.

Don't you hate when lepricons post questions? I doubt it is that because it is consistent in the two samples.

[Chip]

Originally Posted by scootermcq

Don't you hate when lepricons post questions?

Or maybe a naked Martian?

(I wish I had something of substance to add to this thread.)