How does a newtonian reflecting telescope work?
Betafett asked:
My new telescope has piqued my curiosity–More specifically, why is it that when looking into the eyepiece we don’t see the cross shaped mount for the diagonal mirror (or the mirror itself?) in the image? I can’t get my head around the problem and it’s been so long since I did optic physics that I’ve pretty much forgot how it all worked….
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My new telescope has piqued my curiosity–More specifically, why is it that when looking into the eyepiece we don’t see the cross shaped mount for the diagonal mirror (or the mirror itself?) in the image? I can’t get my head around the problem and it’s been so long since I did optic physics that I’ve pretty much forgot how it all worked….
February 3rd, 2010 at 6:13 pm
The eye piece covers only the diagonal mirror area. It does not show the spider upon which the small diagonal mirror is fixed.
The reflections from main mirror is focussed into a point where the diagonal mirror is placed.The field of eye piuece covers only this diagonal mirror area. Chandramohan P.R
February 4th, 2010 at 2:49 pm
The central obstruction is before the light is focussed by the telescope. Consider a star anywhere in the field of view. What point of the mirror does the light from that star hit? It should be obvious that if you ignore the central obstruction the light from that one star shines on the entire surface of the mirror, not just one point.
The whole job of the telescope is to sort out these rays of light so that there is a 1:1 correlation between the _direction_ of incoming light rays and the _position_ of those light rays on the focal plane. So the light of stars in the middle of the field of view hit the edges of the mirror and are directed to the centre of the image further along the optical path.
The “hole” in the image is all over the image in the form of lost light making a dimmer image, not concentrated in one position of the resulting image. Andrew S
February 5th, 2010 at 11:36 pm
You can’t see the spider vanes for the mirror because their simply too close. Maybe thats too simple of an answer. but you can’t see it for the same reason you cant see a pencil held right in front of a pair of binoculars. To bring it into focus an object needs to be much further away. Fred