Re: ATM 4" scope plans...

["Shane LaPierre" <shanelapierre@dellnet.com>]

> Some of you may have read about my 'friends and family' scope making
> plan, where I plan to make a handful of simple 4" scopes as gifts for
> friends and family (to encourage them to look up once in a while).
>
> I have the glass for the first 3 of these, and I wanted to run my
> basic plans by you all to get a reality check. As a point of
> information, my only experience to date is the 6" f/6 (spherical)
> dob scope I just completed
>
> - first goal -- keep it simple and inexpensive.
>
> - 4" f/5's. Is this a reasonable focal length? Will it be difficult to
> parabolize (unlike the 6", I want to go all the way with these as
> experience for the 16" will do for myself next).

I think you will find a 4" tougher than a 6".  It's just small, but you'll
be fine.


> - PVC pipe for the OTA -- I know it sweats, and isn't too stable, but
> I don't see many non-wood alternatives for this, and this is small
> enough I don't think it will hurt (we're talking like 18" total ota
> length here).

I don't see any problems.

> - A simple fork type mount -- I am envisioning these as being table
> top scopes, not used for anything but casual moon and planet gazing,
> and I really want to make them easy to setup, move, and not be in
> multiple pieces. Is a fork mount (wood?) reasonable?

Forks are great... especially while eating.  Are you going for alt-az or
equatorial?  I would stick with alt-az in this size.  The small dob is
basically a fork alt-az mounting.

> - A stiff single wire diagonal holder.

It'll work, but at F5 collimation is particular if you plan on doing
high-power (as far as 4" go)

> - Some kind of homemade friction fit focuser -- I have heard of these
> being made from pipe fittings, etc, is that right?
>
> - A simple push/pull bolt cell made from some thin hardwood.
>
> - Should I make the diagonals too? Will I save much money?
>
> So that is the plan in a nutshell. I am trying to keep construction of
> each under $100. The glass was $20, so I have $80 left for the rest.
>
> Any comments, suggestions, etc would be really appreciated.

Sounds like fun.

Good luck.
Shane LaPierre,
http://www.geocities.com/stellar1972