CN FORUMS ARCHIVE Telescope Reviews: Adjustable wedge

Here's an adjustable wedge I just built for my Questar Standard 3.5. It's designed to mount on a decades-old Bogen 3030 tripod from which I removed the rack-and-pinion elevator shaft and attached tilt-head. The rest of the tripod was left intact.

Until now, I've been using a fixed wedge that's set for my home latitude of 39 degrees. Travel plans convinced me it was time to build something a bit more versatile. This one has a 25-degree range of adjustment, suitable for latitudes from 25 to 50, and thus will work anywhere in the lower forty-eight states.

I already had all of the materials on hand as scrap or surplus from other projects. I didn't draw detailed plans, but relied on a bunch of conceptual sketches. Most dimensions are non-critical, but layout of the sliding arcs (is there a better term?) and accurate hinge placement took some thought and careful construction to ensure smooth operation over the entire range of adjustment.

I stacked and glued 1/2-inch Baltic birch plywood to create one-inch-thick (nominal) construction blanks for structural members. The sliding arcs are 1/2" thick. Beneath the bottom plate, I fastened a turned disc of 1/4" MDF which fits snugly down inside the tripod's center column to act as a hub for azimuth adjustments. The wedge attaches to the tripod with a length of 3/8" all-thread which runs through the center column and is secured at top and bottom with wing nuts. I turned a plywood stopper which fits into the center column at the bottom and provides a bearing surface for a washer and the lower wing nut. The upper wing nut bears against a washer atop a stout alloy disc which is about the same diameter as the tripod's collar casting. The heavy disc is actually a table saw blade-stiffener -- an extra one I had lying around my shop. I recall paying less than $15 for a pair of them a few years ago.

I fretted a good bit about the tilt-mechanism, finally opting to use a pair of 2" solid brass hinges of decent blister-pack quality. Though inexpensive, they exhibit no unwanted play and are perfectly adequate for the task. Plastic bumpers act as a third hand to help position and support the scope for attachment to the mounting plate.

There's nothing fancy about this wedge, and I don't even plan to apply a finish. I'm far more interested in robust performance than style-points, and this wedge, though relatively light in weight, is rock-solid. The vertical cherry inlay on the upright member isn't decorative. Rather, it serves as a reference line for the protractor I use to set the tilt of the mounting plate. I don't trust the accuracy of the little plastic bulls-eye and dual-axis levels on the market and didn't install any on the bottom plate. Instead, I use a small torpedo level to level the wedge before mounting the telescope.

When I observe, I keep the tripod legs fully retracted for the sake of maximum stability. Induced vibrations damp immediately. With the scope aimed at the celestial equator, eyepieces are about 35" above ground-level, a perfect height for me when I sit in my cheap plastic patio (observing) chair. I haven't decided whether or not I should also drill the bottom plate to hold extra eyepieces. Right now, it's a handy place to park the Powerguide II and a red LED flashlight. Perhaps I'll make an accessory shelf to mount on the trip somewhere below the wedge.

In the event I need the tripod for photography or other purposes, I can remove the wedge and reinstall the original Bogen elevator shaft and tilt-head in less than a minute.

The tripod is held together only with screws. I chose not to use glue because I may yet decide to fit the wedge with some kind of micrometer adjustment and would probably need to disassemble it, at least partially, to make that modification.

There's no doubt this simple home-built wedge lacks the sophistication and panache of Questar's elegant Tri-Stand, but it meets all of my needs. Best of all, it didn't carry a $1000+ price tag.

Tomorrow, I'm heading south to see what the moon looks like over New Mexico.

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Questar 3.5 standard - pyrex and BB coatings
Powerguide II
8mm, 12mm, 16mm, 24mm and 32mm Brandons
Homebuilt Galileo scope and very large and ugly homemade tripod
11 X 56 Oberwerk binoculars
other odds and ends, including iPod Touch (and now iPad, too) with StarMap Pro (what a marvelous combo)...

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"Nothing exists but atoms and empty space. Everything else is opinion."
Titus Lucretius Carus 99-55 B.C.