Camera problem

[Terry St]

Sometimes, when I take a picture with my 40d the automatic shutter speeds that display can fluctuate dramatically from 100th of a second to 10th of second in just a split second before I press the shutter, leaving me with an overexposed picture. Why does this fluctuation happen?

 

[AndyB1976]

Are you photographing a changing scene/light conditions when this happens?

 

[TCR4x4]

What are you focusing on? What metering mode etc etc.

Some pictures with the exif will help too.

 

[AJQS]

Sounds like you're in spot metering, which will flit about all over the place as you're moving about slightly and pointing it at things requiring different exposure times.