Differential exposure with 30D on occasion

[dakotah_jackson]

Attached is an image that shows a problem with exposure that shows up from time

to time. Camera is a 30D. Lenses vary. This exposure differential does not

happen often but every few hundred to a thousand or so exposures I get one like

this.

 

The frames before and after are fine.

 

Any idea what the cause may be?

 

While we are at it I get different exposures from frame to frame every now and

then. Same framing but in a burst of 3 or more I will get varied exposure with

basically the same framing... just action in the area as the reason for the

burst shooting. The placement of the light and dark doesn't change, just the

exposure in the image. I do not have the camera set for any kind of exposure

bracketing. Would be dumb to shoot action and try to bracket it. Just odd and

frustrating to have to work on some images because of over or underexposure when

they all should be done as I want without the camera changing it. Any ideas or

help here would be appreciated as well.<div></div>

[JosvanEekelen]

Might be a shutter problem. Check for a relation of the phenomenon and shutter speed. I'd expect it to occur more with shorter shutter speeds. Although the 30D does not carry an official shutter rating unofficially it is good for about 100.000 shots. This is no guarantee that it will fail soon after reaching that number but problems can be related to this. If the camera is still under warranty I'd send it back to Canon.

[hjoseph7]

I sometimes get this but is very rare, when trying to photograph objects in different lighting conditions. Such as trying to photograph a computer monitor under Tungsten light.

[mark u]

It's possible that it is shutter related, but I think that the sharpness of division between the two areas of the image mean that the camera is actually shooting at two different ISOs because the amplification voltage isn't being applied to part of the sensor - an intermittent electrical fault. Have you seen this problem shooting at 100 ISO, or only at higher settings?

[tommyinca]

Most likely explanation is the shutter is sticky and drag during part of the frame. This can explain why part of the frame is a bit "over" explosed.

[William Michael]

>>> Any idea what the cause may be? <<<

 

I would be more confident with an educated guess as to what it is not: I do not think it is shutter related.

 

There are two reasons for this opinion:

 

1. If it were shutter related the line of differentiation would be curved not straight.

 

2. If it were shutter it would be more likely to be regular (i.e. every frame) as the shutter is packing it in.

 

 

The randomness of the incidence and the accuracy of the line of differentiation of the frame make me guess: ISO / sensitivity / software / firm ware random hiccup.

 

If you have kept all the images it happens with it would be good to investigate the EXIF of each to analyse any identical detail.

 

WW

[eric_lawson1]

"If you have kept all the images it happens with it would be good to investigate the EXIF of each to analyze any identical detail."

 

This is why I keep coming back to these forums, what an intelligent suggestion to identify the problem.