[Lester]

Hi all, I have been testing some of my camera lenses on Canon 20Da. The first is a Sigma 18-200mmDC lens. I sat down and focused it onto the TV and could fit in just over half the width of the screen. Then I fitted an old MD (minolta 35mm film type lens) Tokina 200mm, with MD-Eos adapter. I could fit in just over half the FOV of the Sigma lens at 200mm.

I realise with the size chip of the 20Da, that you magnify the FL by 1.6 when compared to standard 35mm film lenses. So I think the old Tokina 200mm lens is actually 320mm when on the 20Da. Is this correct? Also this lens is f3.5 wide open, so is it still f3.5 when on the 20Da? Or should the f3.5 be multiplied also by 1.6?

Another question; when I mount the 20Da or 40D cameras onto my telescopes, should the FL of the scopes be also magnified by 1.6?

I hope someone can understand my questions. Thanks.