Over-exposure with shallow aperture - can anyone diagnose? Canon 30d

Urban Grimshaw

Urban Grimshaw

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I've experienced this several times recently. Shooting in AV mode (which is what I use 99% of the time) the camera has consistently and massively exposed shots at medium to shallow apertures, yet if I stop it down to say f1.8 or f2.8 the exposure is much more what you would expect.

Obviously I've checked to see if I'm not missing anything silly, but the shutter speed is being updated in the display as it should, so I can't fathom why it would do this. It doesn't tie in with what the display is showing. Even if I drop the exposure compensation down to -2 it still comes out over-exposed.

There are two things to note about the camera:

Back in the summer I dropped my nifty fifty and broke a little bit of the plastic facia around the mount. The lens still works perfectly in itself, but when I first put it back on the camera there was a little bit of plastic protruding slightly and let's say it took a little bit of persuasion to remove again! This one act I believe may have slightly bent one of the 3 retractable prongs on the body - at least one of which doesn't always pop out and has caused some intermittent autofocus issues and error 99s (which I assume is communication with the lens).

The camera also gets exposed to some cold conditions (sometimes zero and below) unprotected for long prolonged periods.

Could it be caused by communication problems with lens, similar to the autofocus issues? Incidentally it was the nifty fifty I was using today when it happened, so possibly the lens too - I don't recall which lenses it has happened with in the past though.
 
Can you post an example image of what a normal exposure is like? Also how much are you stopping your lens down to get to f/1.8? Do you have a 50/1.4? Exif data would also be useful for any shots you post.
 
It sounds as though your nifty has taken exception to rough handling. I think the aperture blades are sticking so that they are not closing down the aperture fully at the moment the shot is taken.
 
Yellowbelly said:
It sounds as though your nifty has taken exception to rough handling. I think the aperture blades are sticking so that they are not closing down the aperture fully at the moment the shot is taken.
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Fits the symptoms - it's always wide open, not stopping down. The chances of a nifty-50 surviving a drop are remote.
 
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The lens is the Canon 50mm f1.8. Exposure fine at f1.8. Completely blown (almost a complete white-out) at say f10.

It sounds as though your nifty has taken exception to rough handling. I think the aperture blades are sticking so that they are not closing down the aperture fully at the moment the shot is taken.
Click to expand...

This makes a lot of sense and was along the lines of what I was thinking. So the blades rest at open, and only close down when you take the pic?

Do you think the cold could contribute - blades freezing, etc?
 
Yep. Sounds like your blades are stuck.

And yeah, the aperture only stops down when you actuate the shutter or hold the DoF preview button. At the widest aperture, the camera receives more light to go to the AF module and achieve proper focus.
 
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ChrisJ_SLH said:
Would agree with the above. Try setting a narrow aperture and pressing the DOF preview button, if the view-finder doesn't darken instantly when pressed then this would back up the theory of sticking aperture blades.
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Just tried, and tried with another lens (which worked perfectly).

I guess I've found the source of the problem :'(

Most of it's usage is at f1.8 though, so it won't be relegated to the bin just yet.
 
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