Posts Made By: Sam Greenlaw

We recommend Bob Fies.

http://home.covad.net/~alcoat/index.htm

Simple, cheap, reliable.

His simple approach uses aluminum. Fewer problems than with exotic coatings.

Spectacular.

Construction details, particularly, show years of brain-work. This is one heck of an 18" scope. Not all that hard to build once the design is thought through. (I'm stealing all I can carry.)

By the way: http://antwrp.gsfc.nasa.gov/apod/astropix.html

The December 1, 2003, picture. It's way off topic.

Looks impossible.... ;^)

Assuming that you are going to use silicon glue, a small coin works fine.

This is not critical.

If you're interested in a Christmas tree looking mirror cell, here's what it's like for a 16 inch. Imagine this mess with the cell triangle folder thingies.

This is an easy thing to make.

Takes time to cut and bend the aluminum. About one good long TV or VCR movie. I carried in a little 3" vise from the garage. Set up shop on a yoga towel.

Then drill 39 holes and connect. Experiment, here, is that I used automotive fuel hose over 1/4-20 bolts. Fuel hose is impervious to everything. 3/4" length, tightened to hand-tight plus 1/8 turn.

How's that for heavy duty science? ... ;^)

[Triangles: The folded sides meet. These edges make nice places for epoxy. Conservative design, a lonely epoxy dispenser, whatever.]

The bottom is the usual pair of 3/4" plywood pieces with holes in the middles. (Ads for Dunkin Doughnuts?) The usual adjustment knobs. This bottom set also holds the fittings for trusses and strings.

Mine's truly, abysmally ugly. Prototypical.

So, blow the f#$%er to bits !

And his mother and little sister, too.

Use the 007-meganuke Red Button.


New weapon for enhanced "Sin City" video games.....

The full length inflatible tube sounds cumbersome.

Trusses, though, are a possibility with an enclosed tube. The main aim would be to dampen vibes.

Imagine a straight bicycle tube that fits inside a truss.

Put the inflated tube inside a very thin metal tube, like my shower rod trusses. Pump it up to 60 psi. The tube could stay pressurized, like the bicycle tube.

Instead of having to use tensioned kevlar or nylon strings, the inflated tube might do the trick for eliminating vibes.

Installing tensioned strings is easy to do. Works O.K.

I don't know about inflatibles. Just an idea.

A dial guage works great.

A little geometry compass works, too. K.I.S.S.

The scatter effect is the main problem.

The big problem is light from local background pollution. It enters from all angles. It sets up a little symphony in there.

Baffles eat it up.

This is an argument for slightly wider tubes, too. More room for baffles. Same entry diameter with a top baffle, but more chance to get darker later.

I established a Group over on Yahoo for owners, orderers of Obsidian Optics mirrors. This was done after I won an auction over on eBay for a 16" mirror.

As a guess, you're looking at a similar mirror.

As to thickness: the problem is to get an adequate mirror cell. Since PLOP came along this is not a difficult problem. A standard door plate converts to a 27-point cell for a 16" mirror. (Folded-side triangles are fine. Each point gets a whole 1# force on it.) Don't quite believe models that show super results with 9-point setups.

Pyrex gets the nod. It's easier to work for final polishing, so usually you get better finishing. Better mirrors.

http://groups.yahoo.com/group/obsidian_optics_mirrors/

There have been a few guys whose orders got lost in the mess at Mark's shop and from bad deliveries from his glass suppliers. At present this seems to be straightening out at a rapid pace.

It's no more than three overdue orders now in comparison with several dozen happy campers.

We also recommend a coater and have some tips for construction.

However, be sure to pay with a credit card or other recoverable purchasing medium. If an order falls behind by a year, you need to be able to get a refund. That's not happening now, the long delays, but you never really know dealing with a small business that has long delivery schedules.

Good luck !

The problem with the $300 budget is that you don't have the money to buy a ready-made scope with a good mount, and basic books and sky map info.

Going ready-made: a pair of 9x63 binoculars from Orion, a decent tripod, and books: Nightwatch, Finding the Constellations, and either Touring the Universe through Binoculars or Binocular Astronomy.

9x63's are $189 list; a tripod and adapter go around $60; the books maybe another $70. Close enough.

The tripod will work best with a parallelogram balanced holder, but that's $250 ready-made. ($25 do-it-yourself.)

Going do-it-yourself: Buy a mirror off eBay. Built a Dobson scope from Sidewalk Astronomer plans. Borrow lots of idea from this Forum. Get books, too.

6" mirror's all of $35 with shipping. 8" gets you close to $80 total. Other hardware costs $50 or 75. Bill of materials for the tube, pivots, base maybe $50 asuming you have/can beg use of tools. Call it $200 for the 8" scope.

Eyepieces come up here and eBay, cheap. You're not likely to be using more than 200x with a beginner scope. For the 8" f/6 (FL 1200mm) that's a 6mm. Buy a 12mm, a 40mm and a 2x Barlow. (We all have extras.....) $20 each is fine for starters. You'll find out what's next......

And buy books. nightwatch, finding the constellations, and a map book. Or download map information.

>>>> $300 is a challenge. Buy a $300 boat and see what happens...... ;^)