Problem: *ist DL, mirror lens in Av mode

Greetings All,

I have a mirror lens which i use on occassions but have noticed the following behaviour, i thought someone could perhaps explain why? When i use this lens in Av mode which should work fine becuase they are a constant aperture, the images come out under exposed, very underexposed. However when i switch to full manual mode and then use the AE-L button to get the correct exposure the exposure is as it should be, fairly accuate.

Has anyone experienced this before? I would have thought that they would behave similarly (given the fixed aperture) the only difference would be that i am telling the camera to "take an meter reading now".

any ideas? Its probably something obvious im not thinking of.

Thanks

What's the make of the lens ?

The lens is a Soligor 500-800 zoom lens (id never seen a zoom mirror lens before this one). Will brand make a difference?

My first thought on this is that a 500-800mm mirror zoom will not have a constant aperture. If it starts at f8, then it could be f11 or f16 by the time it gets to 800mm. Maybe this is a clue as to why you are getting under-exposure. Try it again and see if the lens is OK at 500mm but not at 800mm and if this is the case we have the answer.