How to build a useful grab-n-go telescope on a budget!

Three simple small scopes

No. 1, a four-inch refractor:

Late last year, I realized that I wasn't using my larger reflectors very much any more because they took so long to haul outside and set up. Often, all I wanted was a quick look at one of the planets, the moon, or some other bright object. It was then I decided to build this scope, something I could pick up and haul outside in one trip. I can take a quick look, maybe take a picture, and then carry it quickly back inside. It turned out to be the scope I use more often than any other. If this sounds like you, read along!

I listed six major requirements when I started looking:

• Portability. I wanted to be able to carry it outside in one trip.
• No central obstruction. Obviously, a refractor. I guess a small Mak-Cas would have been a good compromise.
• Affordability. I didn't want to spend the money on an apochromat, so I looked for a Japanese achromat, preferably one by Vixen.
• Stability. Typically, commercially available telescopes are supplied with a mount that just barely holds the scope. Ideally, the mount should cost as much or more than the scope if you want a stability and good tracking.
• Wooden tripod legs. To dampen out vibrations quickly. Also, they're cheaper than heavy aluminum legs, and lighter than heavy steel legs. Nothing is worse than cheap aluminum tripod legs.
• Automatic motor drive with manual override. GPS Go-To scopes are wonderful, but just more stuff to fool with.
• I'd like to do a little casual astrophotography--sun, moon, planets, bright objects.

I decided that a four-inch refractor would offer the most portability when combined with a heavy mount. My six-inch refractor sits idly in my study because it just takes too long to set up. I wanted to be able to carry the entire setup outside in one trip. The Celestron 4-inch refractor (shown in the photo) is sold with the CG4 mount. Feeling that the CG4 is too light for this scope, I bought a used Optical Tube Assembly and a used CG5 mount.

The CG5 mount is one of the best values for the money on the market today, but it is notorious for a couple of problems that are easily fixed. You can pick up a new mount for about $300 anywhere, and a used one for about $200, but be prepared to do a little work on it. The drive (below) is available from several sources for about $150. The motors attach to each axis and the hand control allows slewing at 2X 4X and 8X speeds in any one of four directions. When the unit is turned on, it automatically tracks the stars at the sidereal rate. A 12V battery pack holds four D cells.

Note the wooden tripod. Not only is it much nicer looking than the original aluminum, but it is more stable and allows vibrations to dampen out much more quickly. This one is maple. The light color makes it easier to see and harder to trip over in the dark. A great website for building a wooden tripod: Astronomyboy.com.

A new CG5 mount is lubricated with a substance that thickens like old glue in cold weather. The gears become so locked up that they won't even turn under power from the motors. This problem is covered in detail on a number of sites, and one site in particular gives precise instructions for dismanteling, deburring, and relubricating the mount. It takes about four hours if you haven't done it before but the result is more than worth the time. I used a lithium based marine lubricant, and the result is that you can turn the gear axles with your fingers, even in the cold. Complete instructions for overhauling this mount may be found at www.astronomyboy.com.

Here's a modification that I haven't seen mentioned anywhere else. This is the most fragile part of the mount. The connector on the declination drive is just a thin piece of circuit board with a telephone jack soldered onto it. The board sticks out into space, unsupported. After a number of users reported that this small connector had broken off, I fashioned this protective cover to keep it from getting damaged. The small wooden brace underneath keeps it from flexing downward and breaking from tugging on the cord (see photo below). The cover can easily be made by bending a small square of aluminum. Two holes are drilled directly into the bracket on the mount and threaded to accept two small screws. Don't worry about drilling the holes in your mount since the cover will probably never be removed. You could also superglue it on, but the screws are more permanent.

The tag indicates that this refractor was made in Japan, not in China. There is nothing wrong with the new Chinese refractors imported by Celestron-- they are wonderful instruments and still represent an excellent value for the money. But the older ones were made by Vixen for Celestron and are noticably higher in optical quality. These are sometimes found on the used market. If you can find one with the "Made for Celestron in Japan" label, consider yourself lucky!

Another simple upgrade: replacing the plastic focusing knobs with a pair of precision machined aluminum knobs. Not only are the knobs easier to see in the dark, but it's easier to focus more precisely. The knobs are available from www.focusknobs.com

I replaced the six-inch mounting bar with the fifteen-inch bar shown in the photo. This allows the scope to slide back and forth easily to balance it when you add a camera. Much easier than loosening the rings! The extra long bar is available from Hands On Optics.

As of January of 2008, inexpensive (under $3000.00) apochromatic 4-inch telescopes are now available from Orion, Stellarvue, Williams Optics, and other manufacturers. Most of these use a doublet with ED glass to give color-free images. The short focal length makes them even more portable.