[ATM] Cheap Optics for Public Terrestrial Telescope?

["David Sleeter" <d.sleeter@roadrunner.com>]

Hi Folks:

First of all I'd like to thank the people who responded to my question about
a cylindrical cage-style tube for a 16" Newtonian. Their suggestions were
helpful.

Regarding my current question, In addition to my interest in telescopes, I'm
a volunteer building a hiking trail on a 1,000-foot mountain at the edge of
our neighborhood here in Moreno Valley in Southern Calif. It's my daily
exercise, and I've been working on it for 6 years. As the trail has grown in
length, access to the mountain top has become easier. When I started, I'd
see maybe 1 or 2 sets of fresh footprints per week. Now hardly a day goes by
when someone doesn't hike to the top, and on weekends, I see entire families
making the climb just to enjoy the spectacular view.

>From the top you can see all over Southern California. To the South and the
East are Mt. Palomar and Mt. San Jacinto. To the West and Northwest, Mt.
Wilson and Mt. Baldy, and to the North, Lake Arrowhead and the San
Bernardino Mountains, and to the East, the 12,000-foot peak of Mt. San
Gorgonio.

This past week it occurred to me how nice it would be to have a
permanently-mounted terrestrial telescope up there that hikers could use to
look at the many points of interest around them. I'm thinking something
heavy and "clunky-looking" that wouldn't be worth stealing, but optically
good enough to provide a nice view.

I have a machine shop, so I could make it myself, and I'm thinking that I'd
probably make it from PVC plastic pipe, put it on an alt-azimuth mount made
of galvanized steel pipe, and use inexpensive optics to keep the cost down.
I'd make the eyepiece drawtube the simple slide-focus type with a stop on
the inner end. Then I'd glue the whole scope together so it would be
weather-proof, and so that you'd have to cut it apart to get the lenses out.
I'd weather-seal the slide-focuser with greased o'rings.

The optics I'm thinking I'll need will be an achromatic objective from 50 to
80mm. in diameter, achromatic lenses suitable for making a Plossl-style
eyepiece (1-1/4" would be o.k., but lenses for a 2" eyepiece would be even
nicer), and an erecting prism, and I'd like to make the magnification in the
10X to 20X range.

Regarding the fate of the telescope once it's in place, I'm guessing that if
I make it homely-looking, that will discourage people from trying to steal
it. About 6 months ago I put up signs asking people on motorcycles to avoid
riding on the trail (motorcycles were becoming a problem), and both I and
the neighbors have been pleased with how well the people who use the
mountain are now respecting those signs. If I include an appropriate sign on
the telescope, I think there's a pretty good chance that people will respect
it too.

In surfing the net today, I've found numerous good deals on objective
lenses, and potential eyepiece lens sets (I could even cannibalize a Rini
eyepiece), but I'm striking out on the unmounted erecting prisms. All
suggestions on sources for cheap objective lenses, eyepiece lenses, and
erecting prisms will be greatly appreciated.

Regarding the optics, with the understanding that the scope might be stolen
or damaged, and that I'll eventually want to make another, it would be nice
to find sources where I could buy replacement lenses and prisms if needed.

Finally, I've seen a new scope sold by Apogee. It's called a "Beer Bottle"
telescope, and because the ads all say it can be used as a spotting scope,
I'm guessing that it has a built-in erecting prism. But I can't find any
descriptions of this scope that verify my assumption. With its 50mm.
objective and its 18X magnification, it might contain all the optics I need
in one package, and though it's physically smaller than what I'd like, with
its low internet price of $19.95, it's certainly cheap enough. Anyone looked
through one of these? Any opinions on the Apogee Beer Bottle scope would
also be appreciated.

Dave Sleeter/Moreno Valley, CA




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