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Re: [arrettinator] two parallel lines can cross!!!:
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petsfed
Jan 19, 2007, 10:46 PM
Views: 1073
Registered: Sep 25, 2002
Posts: 8599
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arrettinator wrote: petsfed wrote: /physics and astronomy student near graduation Totally off topic but, I'm thinking of building a style of Gregorian/Folded Newtonian telescope. I have a 6" f/5 parabolic primary. Think of a folded newtonian, but instead of a flat secondary I want to use a spherical secondary. I'm having trouble figuring out what fl secondary to use. I'm thinking it's going to be a 2" spherical w/ a smaller flat diagonal, as well. This is just me brainstorming. I've got the newtonian design already for this primary, but am bored with it already. I am losing illumination w/ the bigger secondary, but I can't afford a bigger primary. I'll probably get at least an 8" primary, or 10" some day, but for now this is what I'm working with. Any suggestions. (drawing not to scale, obviously)
Man, I wish I was in an instrumentation focussed department. Dunno what to tell you. I mean, obviously you're gonna lose precision the smaller a secondary mirror you go, but you can't have too big of a secondary or else your light gathering ability is lost. And for a mirror as small as an 8 or a 10, that's pretty significant. I don't doubt you're familiar with spherical aberration so I won't bore you with that, but I'm curious how much additional aberration you're introducing by using one as the secondary (as opposed to a not-necessarily-spherical ellipsoid mirror). As I recall aberration between mirrors is multiplicative, so you could run the equations between aberration of your mirror combinations and total light lost due to a larger secondary and find out what the best combo would be.
That is, I'd plot the product of the expected resolution (or percent abberation, if available, but it should be proportionate to the inverse of the expected resolution) of your mirror system (y-axis) vs. secondary mirror diameter (x-axis), then plot light arriving on the primary (y-axis) vs. secondary mirror diameter (x-axis), then compare the two plots. Where aberration is the lowest while still having a maximum area of the primary not obscured, that's the way to go.
Good luck man. I don't really do too much telescope building in my field.
(This post was edited by petsfed on Jan 19, 2007, 10:47 PM)
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Post edited by petsfed
() on Jan 19, 2007, 10:47 PM
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