Thanks for taking all this trouble, hka, to help me. Much appreciated. It looks as if the diffused cover which doesn't have a plastic white dome underneath is the correct one for selective integral measuring. This leave me wondering what the cover with the inverted white plastic dome underneath and the 17mm opening on top of the dome is for.

I had assumed that with a hole which was 17mm this was the one which allowed you to measure more accurately smaller areas(17mm areas) on the projected negative.

Well my logic was wrong but leaves the mystery of the cover with the inverted plastic dome.

I think I have counted at least 7 Colorstar user here on APUG . Surely I can't be the only one with this cover, can I?

You are the only one who has responded to the thread and thank goodness you have. If I want to find out what the other cover is for, it looks like I might have to PM each of the other users individually.

Many thanks