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Jerry's big Astroscan: more than a mere novelty project, this instrument amplifies the virtues of the venerable Edmund telescope.

You can't help but smile when looking at the picture below. Readers familiar with the iconic Astroscan telescope introduced by Edmund Scientific in the 1970s might think that the image is one of those clever Photoshop fakes that show up on the internet. But no, the giant Astroscan is as real as its creator, science-fiction writer and avid telescope maker Jerry Oltion.

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Although Jerry's giant Astroscan lacks the compact size and portability of the original 4Vs-inch Edmund scope, it delivers nearly four times the light-gathering power thanks to its 8-inch f/4.2 primary mirror. Most of us would consider that a worthwhile trade-off". And while the scope's resemblance to its predecessor is obvious, it actually owes much of its DNA to Jerry's trackball telescope, featured in this magazine's August 2006 issue, page 100. "When I showed my trackball scope at various star parties, people would look at the spherical base and ask if I'd modeled it after the Astroscan," Jerry recalls. "I hadn't, but those comments planted the idea."

So he ground and figured the 8-inch primary mirror and set to work making the spherical back end of the scope. Retracing some of the same steps he took while building the trackball telescope, Jerry found a supplier of large, acrylic lighting globes and ordered a 20-inch sphere. Unfortunately, it proved to be much too flimsy to work without reinforcement. "The spherical section of my previous trackball scopes was made of fiberglass that I had molded over a child's rubber ball," Jerry recounts. "So it was simple enough to add a reinforcing layer of fiberglass to the acrylic ball--but this time on the inside." This approach meant the ball would have a nice, exterior finish without laborious sanding. As a bonus, it also yielded a rough-textured interior, which helps suppress scattered light when painted black.

To keep the big Astroscan portable, Jerry equipped his scope with a removable upper section. The 11-inchdiameter tube was made from a plastic trash can fitted with a series of reinforcing rings that do double duty as light baffles. The ring at the bottom of the tube has four keyhole slots that engage the heads of bolts mounted on the top of the ball, as shown in the photograph at top left on the facing page. Separating the two parts is easy. "You don't have to unscrew anything to remove the upper tube section," Jerry reports. "Just hold the ball with your knees and give the upper tube a little twist while lifting it upward."

Central to the look of the Edmund Astroscan is the integrated rubber-roller focuser--an aftermarket focuser for the bigger version simply wouldn't do. The focuser Jerry built consists of two pieces of Vs-inch-thick PVC sheet. He heated the parts with a candle and bent one of them into a U shape, and the other into an L. He glued them together and sanded them until the joints were invisible. As Jerry explains, "The focuser was the make-or-break component--it would either make the scope look fabulous, or funky."

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While doing everything possible to keep his scope true to the original, Jerry's 8-inch contains several notable upgrades. One of the most important is that the primary mirror can be collimated. This is accomplished by using a special long tool he built to reach down the front of the scope to turn spring-loaded adjustment knobs on the primary mirror's cell.

[ILLUSTRATION OMITTED]

Another improvement on Jerry's scope is the curved-vane spider for the secondary mirror used in place of the Astroscan's optical window. "I wanted to use an optical window, but I couldn't find anything optically flat enough at a price I could afford," Jerry notes. "So I did the next best thing to give the scope the same spike-free views--I made a curved spider out of steel cargo strap." As an added bonus, this secondary support won't dew up.

So what's it like to use an 8-inch Astroscan? As one would expect, the views are just like those provided by any other fast Newtonian reflector of the same aperture. But it's the big Astroscan's utility that makes it a winner. "It has very smooth motions and I'm happy to say that the ball doesn't get in the way of my knees as I originally thought it might," says Jerry. "It's a fun scope to use--it's such a silly thing, it's hard not to smile while enjoying the views."

Readers wishing to know more about Jerry's scopes can do so by visiting his website: www.sff.net/people/ j.oltion/.

Contributing editor Gary Seronik has built numerous telescopes and can be contacted through his website, www.garyseronik.com.
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Title Annotation:Telescope Workshop; Jerry Oltion
Author:Seronik, Gary
Publication:Sky & Telescope
Geographic Code:1USA
Date:Sep 1, 2011
Words:778
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