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Re: [ATM] Why Lurie-Houghton telescope very rare in the ATM
Paul, I'll try.
>Why do you feel that above 10" hyperbolic designs make more sense - is it
>because of the difficulty of figuring full aperture correctors above this size, cost
>or some other reason?
As the aperture increases, so do the atmospheric effects, so available resolution decreases. Cost also increase very rapidly. At some point the lines cross and you just can't get any more... It's my guess that for most locations a hyperbolic design will perform as well, be easier to make and cost less at around 12". Sorry, its a guess from the AO research. No hard data.
>If it is remotely practical to attempt a 14" LH, would it be doable slower,
>say f/5 or f/6, or is the corrector much harder to make for a slower primary?
No issue other than $$$, it would be fairly easy to build the optics. You know about ermine violins, right? I'm not knocking the LH either, it's pretty slick. I don't think it would be all that hard to build 20" from a pure construction point of view. The software that comes with R&V will set up the numbers for you and give you a good idea as to performance. FWIW: At 14" I'd do the Hyperbolic or a corrected Newtonian, but that's me.
>You said cost is a factor, would I be looking at roughly 3x the cost in
>glass of a similar aperture Newtonian?
At least. Lens blanks (plano-plano, fine ground, BK-7) were about the same price as the Pyrex blank at 8". At 14 inchs and current prices I have no idea. Polished balnks can double or tripple costs real fast.
> Also, you say a LH is overkill for CCD work, if I were to buy a ccd camera
> with around a 3/4" chip would I really not see a worthwhile difference?
I have a 1" CCD (1k x 1k) with 25um pixels. If made correctly and aligned properly, my 8" f/4.2 could fill a 2k x 2k... Your 3/4 in chip is well within the diffraction limited correction area of the 8". BTW, best resolution will be with a "f" ratio equal to about 2x "pixel size in microns." So best image resolution with my camera would be at f/50 or so... That gives 2 pixels across the airy disk... To turn that around, with 25um pixels I could probably use an f/4.2 scope with 2 waves of error and see no effects... For the f/4.2 you would need ~2.2um pixels to get the diffraction limited resolution in an image, and very very steady seeing... At 14" I really don't think you would see a difference.
Hope that helps. As alway, your milage may vary...
Greg Jones
http://home.comcast.net/~dac20/dac_001.htm
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