Re: ATM Newbie question on 8" f8

["Andrew Schott" <aschott@digital.net>]

I've done everything but actually grind the mirror on my "scratch" scope
projects.  I'm definitely grinding my next mirror myself and am considering
a 8" f/9 in Zerodur.  I've been using a 6" f/11 for years now and love the
long focal length.  I would like a little more aperture without lengthening
the scope too much.  I'm limited to a 6' tube without having to make it
collapsible.  It's in dreamland now but if the right blank comes along...


----- Original Message -----
From: Brian Lloyd-Newberry <newbeb@yahoo.com>
To: <atm@shore.net>
Sent: Wednesday, March 14, 2001 11:11 AM
Subject: ATM Newbie question on 8" f8


>
> Hello all,
>
>    I have for some time wanted to build a scope from scratch (no pun
> intended...), and have been lurking here for awhile and even asked a
> question about hand pain and TM many months ago. I have decided to leap
> off the bridge and have bought pretty much all of the TM books that
> willbell had (much to the wife's dismay).
>
>    In the months to come I am planning on picking up a blank and the
> necessary materials. I am leaning toward an 8" mirror and I know that
> the "rule" has been 6" f8 or 8" f6 for the first mirror. Having used an
> 8" f6 that a friend of mine owns I have determined that I do not want
> to be kneeling that much and I am thinking that an 8" f8 would be
> better for those of us who sit for a living and want to stand upright
> on our free time. ;)
>
>    I am thinking that the eyepiece would end up a little less than 5
> feet from the mirror (in a newtonian config) which when I put the dob
> base on would probably bring it right up to my eye level (5'6" at the
> eyes) at the zenith. My wife might need a "step" to use it at the
> zenith, but that would beat kneeling on the cold and usually wet
> ground.
>
>    Anything I should know about an f8 vs an f6? There will be less
> glass to move and it should grind a little faster, no? The tube will
> obvoiusly be longer (that is the point) but I figure that if
> I build a simple box tube and split it in the middle I can still fit
> the pieces in the trunk of my Honda Civic without trouble, and with the
> box design they won't roll around.
>
>    Another issue is that I am planning on using BVC for the primary
> because it is slightly cheaper (and my wife is already going to kill
> me). Is there anything that I should know about BVC vs. Pyrex/Plate? I
> am guessing that I can use the same process as Textereau outlines with
> possibly more precaution against scratching because the BVC is a little
> softer.
>
>    Thanks for the invaluable information that you all share. I am sure
> that I am soon to be using it more directly. :)
>
> -Brian
>
> Brian S. Lloyd-Newberry
> newbeb@yahoo.com
>
>
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