NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Basics of computing sunrise/sunset
From: Douglas Denny
Date: 2009 Jun 19, 02:17 -0700
From: Douglas Denny
Date: 2009 Jun 19, 02:17 -0700
I disagree with you. Illuminance through an optical system depends on the relative sizes of objective and exit apertures. Ignoring inefficiencies of the lenses, if all the light entering passes through the exit aperture (and in properly designed optical system it should) then the difference in intensity in/out is in the ratio of the square of the diameters of the apertures.(ie their areas). If this was not so - explain please why it is that stars invisible to the naked eye of aperture diam 6mm - because they are too faint (intensity too low to stimulate the retinal cells), become sudenly visible with a telescope of aperture say, 100 mm diam? The answer is in the relative light gathering of the objective aperture being bigger by far than that of the eye, and all that light becomes reduced to the aperture of the eye through the exit pupil of the telscope. Douglas Denny. Chcihester. England. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---