200mm lens translated into telescope inches?

[silv (Annette)]

Hi All

I'm back with another embarrassing question

what does my 18-200mm zoom lens translate into when compared with a telescope? it can't be equal to an 8", can it?

I searched the web for an answer but apparently, nobody has had this question. must be really stupid, then.

thank you.

[Steffen]

At the 200mm end the maximum relative aperture of this lens is f/6.3, hence the aperture is (200mm / 6.3) = 31.75mm = 1.25"

EDIT Photographic lenses are called by their focal length first, the relative aperture (focal ratio) is an important secondary denominator. Telescopes are named by their absolute aperture (often objective or mirror diameter) first and their relative aperture (= focal ratio) second.

Cheers
Steffen.

[silv (Annette)]

merci steffen