docelementary optics- keplerian layout
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elementary optics- keplerian layout
Elementary Optical Concepts A Simple Camera Inverted image Object f b a Thin lens formula: 1/f = (1/a) + (1/b) Elementary Optical Concepts A Simple Camera Inverted image Object f b a Thin lens formula: 1/f = (1/a) + (1/b) Elementary Optical Concepts A Simple Keplerian Telescope Objective lens Eyepiece lens Image feyepiece fobjective Basic layout of the Keplerian telescope. Elementary Optical Concepts A Simple Keplerian Telescope Objective lens Eyepiece lens Image feyepiece fobjective Off-axis light rays Elementary Optical Concepts A Simple Keplerian Telescope Objective lens Eyepiece lens Image Telescopes magnify angles Mag = fobj/feye feyepiece fobjective Telescope magnification Elementary Optical Concepts A Simple Keplerian Telescope Objective lens (Diameter = D) Eyepiece lens Image Pupil diameter = D/Mag Exit pupil Mag = fobj/feye fobjective feyepiece Field plane (or image plane) Fields and Pupils Entrance pupil Elementary Optical Concepts A Simple Keplerian Telescope Objective lens (Diameter = D) Eyepiece lens Image Pupil diameter = D/Mag Exit pupil feyepiece Field plane (or image plane) fobjective Entrance pupil The exit pupil is an image of the entrance pupil formed by the eyepiece lens. Elementary Optical Concepts A Simple Keplerian Telescope Objective lens Eyepiece lens Image The eye is an integral part of the “telescope system” Collimated light: light rays from individual image points are parallel. Elementary Optical Concepts A Simple Keplerian Telescope Objective lens (Diameter = D) Eyepiece lens Image Pupil diameter = D/Mag Exit pupil Telescopes magnify angles Mag = fobj/feye feyepiece Field plane (or image plane) fobjective Entrance pupil “Night glasses” and “richest -field’ telescopes • • • • If the exit pupil of a telescope is bigger than about 7mm, all the light won’t enter our dark-adapted eye A “rich-field” telescope has just the right focal length eyepiece lens to give us all the light we can use and no more The objective lenses of 7x50 binoculars are just the right size to give us all the light we can use from a seven-power telescope Questions – What is the magnification of the telescope in our example? – What’s the “richest-field” objective lens diameter for our telescope? – Why might we want to use a higher power eyepiece, even if it gives us an exit pupil smaller than 7 mm? – What power eyepiece would give us “richest field” performance with an 8-inch diameter telescope with a focal length of 40 inches? – What would be the focal length of a “rich field” eyepiece for our 8-inch, f/5 telescope? – Why wouldn’t we want binoculars with larger diameter objective lenses than 50 mm?
