|
Hi there Bert,
Please remember I am only a beginner and I may be corrected, but I'm almost sure the formula for exit pupil is EP focal length / Telescope focal ratio. Therefore a 10mm EP in a 4.5" f/5 telescope will give you a 2mm exit pupil, while a 10mm EP in a 12" f/5 telescope will give you a 2mm exit pupil. Arpeture does not effect exit pupil if the f/ratio of the two scopes are the same. provided I am correct???
To answer your question about a barlow. Effectively a barlow changes the focal length of the scope and therefore the f/ratio, if it is a 2x barlow the focal length will be doubled, and therefore the f/ratio doubled. This means a barlow should give you a smaller exit pupil for a particular scope and ep. once again, I may be corrected.
If I am wrong someone please correct me, but this is how I understand it.
Hope it helps.
Last edited by NQLD_Newby; 12-09-2007 at 05:41 PM.
|