Image of the day

Captured by
David Marks

Lightning in the desert

My Account

New to Astromart?

Register an account...

Need Help?

Posts Made By: Dick Jacobson

December 29, 2004 05:27 AM Forum: Telescope Making

Power to a secondary heater

Posted By Dick Jacobson

Aluminum is an excellent conductor so that should work, but I'm not sure whether a shroud that's damp from dew could cause a short circuit. Anyone have experience in this?

December 30, 2004 01:30 PM Forum: Equipment Talk

Aperture mask, is this really an Off-axis Newt?

Posted By Dick Jacobson

I understand that off-axis Newt mirrors are made by making a big paraboloid and then cutting the outer portion into circular pieces. So I think you're right, the portion of the mirror that is exposed is exactly like the mirror of an off-axis scope.

January 5, 2005 01:14 PM Forum: Telescope Making

Appleply/Europly distributor near Pittsburgh?

Posted By Dick Jacobson

You might try a Rockler woodworking store (rockler.com), according to their web site they have a Pittsburgh location. They sell "Finnish Birch" which I have used, it's excellent. Don't know whether their 24x30 sheets are big enough for you.

February 6, 2005 07:39 AM Forum: Telescope Making

Making Finder Scope out of old 7 x 50 Binos

Posted By Dick Jacobson

I've made finders out of 7x35 and 10x50 binoculars. I think they work far better than any commercial finders. The straight-through, erect and correct view makes it much easier to locate objects compared with either inverted-view or 1x finders.

The trickiest part to disassembling the binoculars was removing the central focusing mechanism (it sounds like you may already have that problem solved). Starting with Orion "Outsider" binoculars, I used a hammer and a large bolt to remove a tube that was tightly press-fitted inside the rings holding the two sides of the binocular together. Once this was done, you end up with a pair of rings attached to the body of the binocular, and another ring attached to the eyepiece. You can use a bolt and some nuts and washers to hold the eyepiece in place.

One other problem that needs to be solved is to provide crosshairs or something similar to mark the center of the field of view. Instead of crosshairs, I used a tiny machine screw (#0 I think), sharpened at the tip, driven into the focal plane from the side. This works better than crosshairs because the screw is visible in dark skies without illumination.

For a dewcap, I attached a PVC pipe coupling. To attach the finder to the scope, the dewcap is attached with a bolt, and the back end is attached with a pair of turnbuckles. This provides a very solid mount that is easy to adjust even with gloves on.

January 13, 2006 01:04 PM Forum: Telescope Making

Tube cutting

Posted By Dick Jacobson

I've had good results simply using a hand crosscut saw, the same kind that you use to cut wood. Make a line around the tube and support it well on both sides of the cut. Then slowly cut around the tube, keeping the saw nearly tangent to the outside of the tube. It's best to work so the end of the cut is coming towards you, just as if you were cutting a sheet of plywood. This results in a very nice smooth, straight cut.

January 14, 2006 02:57 PM Forum: Telescope Making

Ebony Star discontinued?

Posted By Dick Jacobson

I saw your message today, went to my local Home Depot in a panic and ordered a sheet for $2.83 per sq ft. Ebony Star wasn't crossed off his list, so presumably they still have some in stock; I'll find out for sure in a week or two. The salesman didn't know anything about it being discontinued, but he didn't seem to know much about anything else so I wouldn't be too sure.

January 30, 2006 12:33 PM Forum: Equipment Talk

Parka ?

Posted By Dick Jacobson

The word "Parka" implies an insulated hood that you pull over your head. I find that this restricts visibility too much. Instead, I use a very warm wool cap with an insulated lining that pulls down over my ears down to my neck and closes in the front with Velcro. I call it my Chinese Peasant Cap because that's what it makes me look like. Not very stylish but who cares in the dark!

This, together with a very warm down parka jacket (with the parka hood left down), neck warmer, ski pants, long johns, Sorel boots, heavy wool socks, and ski gloves keeps me warm at zero degrees Fahrenheit.

February 24, 2006 01:36 PM Forum: Beginning Astronomy?

What do you look for in an observing site?

Posted By Dick Jacobson

I found a near-perfect observing site in a wildlife refuge. The area is kept clear of trees so the naturalists can observe the critters with their spotting scopes during the day. At night there is almost no traffic, no light pollution. Good public access and lots of parking areas.

April 5, 2006 01:40 PM Forum: Telescope Making

Is this wild idea possible? (bi-refractor)

Posted By Dick Jacobson

This reminds me of rangefinder binoculars that were sold many years ago. They had long barrels with right-angled prisms at the objectives. There was a hinge at the center so you could use them either like a binocular periscope (barrels together) or a rangefinder (barrels 180 degrees apart). In the second configuration, the objectives would be about 2 or 3 feet apart.

April 6, 2006 01:30 PM Forum: Telescope Making

Is this wild idea possible? (bi-refractor)

Posted By Dick Jacobson

Stu,

Since you and I both seem to be fascinated by bizarro telescope designs, you may be interested to hear about the "Alphorn" telescope I built several years ago. (This was inspired by the Porter turret telescope where the eyepiece stays in a fixed location.) The Alphorn scope was a small refractor with TWO optical flats in front of the objective. These flats allowed you to see any point in the sky while the eyepiece did not move. The tube was always pointed down along the polar axis. I built a mechanism employing a bicycle chain so I could turn one of the mirrors while seated at the eyepiece without reaching way down near the ground where the mirrors were located.

I gave it the name "Alphorn" after the musical instrument it vaguely resembled.

The scope was a dismal failure. Not only was it big and clumsy, but it was nearly impossible to find anything with it. I mounted a right-angle finder scope on the stubby little tube holding the first mirror, but this didn't help much.

Hope you have better luck with your ideas!