Nick
You don't seem to have really been absorbing anything that I have written in this thread. In modern times, the F ratio of the scope is irrelevant to whether the sky is light polluted or not. With the right combination of modern eyepieces ,a fast F ratio scope is capable of the same range of exit pupils/ magnifications as a longer one - so
the F ratio is irrelevant is not a consideration when we are choosing a scope for a light polluted sky. Perceived sky background field brightness is a function of magnification/ exit pupil and not of the F ratio. Do you agree with that ?
Please explain to me exactly what you mean by a ` fast dob optimised for faint fuzzies' not high power ' and maybe we can get somewhere.?
The contrast transfer function of a compound telescope is equaled by an instrument having an unobstructed aperture equal to the diameter of the scope minus the diameter of the secondary mirror so the factor in a typical visually optimised scope would be 1.2X the refractor aperture not 1.5 X...this has been written up in Sky and Telescope a few times.
Quote:
Originally Posted by Wavytone
. Fast dobs optimised for faint fuzzies (not high power) are simply not relevant due to the light pollution. At the moment I am wrestling with Bessel functions in Excel to draw the graphs for you.
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