Matching scope with camera chip size

[Mike JW]

If I use my ultrastar , 0.5 reducer with my C11 then vignetting is obvious, Thus I assume at this F ratio of F5 then the chip is not fully illuminated. If I use the f6.3 reducer there is no vignetting. 

My question - is there a general formula to work out F ratio to chip size such that there is no vignetting (or minimal).

I would like to try different cameras but do not wish to buy one that has the wrong chip size.

Thanks, Mike

[PeterCPC]

If you go to the top of the page and look in Resources/Calculators you will find something called CCD suitability.

Peter

[RobertI]

If you don't get your answer Mike you might have more luck posting in the imaging section .....