[ATM] Re: How fast is too fast?

["Jean-Guy Moreau" <jgmoreau@cablevision.qc.ca>]

Hello Mike, i have not done extensive star test evaluation with this mirror 
and the Paracorr, but if the following photo is any indication, coma is
still pretty well corrected even at f/3.3
Pixels are 7.3 microns square on the detector (Canon 300D)
single 5 minutes exposure ISO 800

http://www.cablevision.qc.ca/astro/NGC7788-90_2.jpg


i agree collimation is not easy, i used the method described in 
Amateur Astronomer's Handbook, by J.B.Sidgwick, pp.206-207
where crosshairs are placed across the focuser end, together with center dots
on the mirrors. Final tuning with a star at high power.

do you figure by hand or machine ?

Jean-Guy


----- Original Message ----- 
From: "Mike Lockwood" <melockwo@uiuc.edu>
To: <atm@atmlist.net>
 
> After figuring several fast mirrors (30" F/3.8, 16" F/4, 8" F/3.9) 
> that all give excellent images with a Paracorr), I can say I 
> definitely enjoy making and using fast mirrors.  I will make more in 
> the future.
> 
> The question is, how fast is too fast?  (In your opinion)
> 
> At what do you think that the Newtonian design really begins to 
> suffer?  F/3.7?  F/3.5?  F/3.3?
> 
> I'm curious to know how the 10" F/3.3 performs with a Paracorr, and 
> how tough it is to collimate.
> 
> Collimation has to become incredibly frustrating at some point, and 
> since the Paracorr was designed for F/4.5 it can only do so much.
> 
> I'm curious to hear others' thoughts.
> 
> Thanks,
> 
> Mike Lockwood
>
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