From: "Bob May" 
To: "atmlist" 
Reply-To: "Bob May" 


Ah, the choices!
Do you go for a nice instrument that you can easily use without the need
for a stepladder or do you go and get the nicer long focal length but need
to have a stepstool step or two to see near the top of the viewing range!
My preference is to see where your eyes are when you get on a single step
(the homemade eyepiece case that you can step on to see things high in the
sky) and consider that to be the focal length that you wish to strive for.
Anything less and the times that the need for magnification will be more
difficult to achieve while anything more will tend to keep the scope from
looking at the stuff that is near overhead at the moment. At 14", the
choices are rather large and I'd suggest the longest that you can feel
comfortable with will be the best choice. Also look at what any particular
EP will give for a FOV if you are more desirable of the larger views.
I'll also note that there is nothing wrong with a partial figuring with the
mirror and you should probably do so.  Since you are making up a stressing
harness, why not do it in reverse (push on the center of the glass while
doing your final polishing) and see how close you can get to a paraboloid
while doing that.  My bet is that you will very nicely do a paraboloid the
first time if you can do a good sphere while the mirror is stressed! Bob
May
http://nav.to/bobmay
bobmay{at}nethere.com
NEW! http://bobmay.astronomy.net

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