I was shooting a band today, one shot was in telephoto with the iris open and a gain of 3db. When I moved to widephoto, I noticed the iris automatically went down to F2, but the 3db was still displayed. However, in widephoto, I could manually open the iris again. The adjustments were on manual, autolock in the middle position.

I understand that this isn't a defect, but what is the principle behind closing the lens during a wideshot? Is it to deepen the depth of field?

This is a normal optical characteristic of some zoom lenses. Other zoom lenses are designed to perform with the same aperture value through the whole zoom range.

It sounds to me Aviv that your shots at full telephoto were under-exposed by half a stop. You were shooting wide open (f/2.4) at +3dB of gain up? Then you pulled back to wide-angle and the camera chose f/2 at the same gain setting?

That would suggest to me that it wanted f/2 in the first place, and your zoom isn't that fast at the 72 mm end. It's nothing at all to do with D of F and all to do with the fact that the max aperture of your zoom varies from f/1.6 to f/2.4 depending on what focal length you're shooting at. All perfectly normal.

tom.