Tips

		Updated
		01-Apr-06
		05/27/01
		10-Dec-06
		22-Jun-03
		24-Nov-06
		19-Jun-05

Click on the links below to navigate directly to the tip of interest

This page contains a list of the some of the techniques I employ on my Dobsonian reflector telescope(s)

Tip #1: Locating "faint fuzzies" with a Telrad and binoculars

Tip #2: Modified collimating adjusters for a Novak secondary holder

Tip #3: Laser collimation technique

Tip #4: Using a de-focused star for an accurate star alignment

Tip #5: Preventing inadvertent battery drain on a laser collimator

Tip #6: Using a large 12v portable fan to cool the primary mirror

Tip #1 - Locating "faint fuzzies" with a Telrad and binoculars

The Telrad (and other "reflex" finders) is probably the single most important piece of equipment for the novice astronomer. Well, the most important AFTER the telescope and eyepiece. The Telrad projects a "bull's eye" pattern onto a clear window against the night sky. You adjust the position of the bull's eye so that it matches where the scope is pointed. Once properly aligned finding objects is fairly easy. And you get the added benefit of knowing where the scope is pointed in relation to the sky and constellations. This is hard to do with a standard finderscope because the image through a finderscope doesn't match what you see in the sky (because of the magnification involved). Star hopping is the best exercise you can use to actually learn how to locate objects in the sky. There will be times when you need more magnification in order to find a particular object because star hopping using naked eye stars won't get you where you need to go. I've found that I can use binoculars and the Telrad in tandem to locate fainter objects. Here's my technique: 1) Turn up the intensity (about 3/4 full with new battery) on the Telrad. 2) Position yourself so that you're behind the Telrad. 3) Locate the object (or "guide stars") in the binoculars. 4) Slowly move the telescope to bring the bull's eye projection into view. What you're doing here is actually looking through the Telrad's projection window with the binoculars. 5) Center the bull's eye over the object and take a peek through the eyepiece. I use a 10x30 set of binoculars which are small enough to easily hold in one hand (leaving your other hand free to move the scope, etc.).
Back to Top

Tip #2 - Modified collimating adjusters for a Novak secondary holder

If you have a Newtonian reflector and must travel to get to your favorite viewing site then you have to learn how to collimate (align) the optics (see Tip #3 below). My Obsession has a Novak secondary mirror holder and I have found this design doesn't lend itself to easy adjustment of the secondary mirror's alignment. Collimation of the Novak holder is supposed to be accomplished by adjusting three phillips head screws with a screw driver. Let me tell you about a certain paranoia that sets in when you are fiddling with a screw driver over a 20" primary mirror: your mind really isn't on the collimation result.

I replaced the three phillips screws with three of the assemblies like the one above. This is a 4" threaded bolt with a wing nut and some "locking" nuts. The two nuts below the wing nut serve to keep the wing nut from moving independently from the bolt. One would probably be sufficient. The two nuts at the other end (the end which screws into the Novak holder) are at a height equal to the length of the original screws. Both nuts are needed to be certain they stay in place. A little black paint and you're ready to go.

The 4" bolts give the right amount of clearance over the vanes of the secondary spider. Collimation adjustments are made by turning the bolts by the wing nuts. Simple, and no tools needed.

Notes: This does add some weight to the top end of the telescope and can throw off the balance of a tube assembly, especially those that don't have much friction in the altitude bearings. If this is a concern then I recommend using aluminum components, or adding a counterweight to the lower end of the tube assembly. If you own a large Obsession or equivalent Dobsonian then you shouldn't have to worry about the extra weight added by these collimating bolts.

Back to Top

Tip #3 - Laser collimation technique

I use a laser collimator which is a real time saver. I had previously used a Cheshire eyepiece but couldn't get consistent results, especially when collimating at night. The basic, no frills, just a single red dot version of the many laser collimators on the market works fine. Laser collimators, while more expensive than a Cheshire eyepiece, are worth every penny. Especially if you're relatively unskilled (like me) on collimating the optics on your telescope or find yourself collimating under low light conditions.

I collimate my telescopes by adjusting the secondary so that the laser dot is dead center on the primary.

Then I adjust the primary mirror so that the laser dot return beam is dead center over the exit of the laser.

Notes: The secondary mirror must first be centered through the focusing tube in order for this technique to be successful. This is usually a one time process and shouldn't need to be repeated very often. Secondary centering can be approximated (and monitored) by looking through the focusing tube and positioning the secondary mirror holder so that the mirror is the centered within the tube. If the edges of the secondary mirror are seen then reposition until 1) no edges are seen, or 2) the same amount of edge is seen all the way around the tube. A more accurate centering can be made by following the technique described on page 290 in Kriege and Berry's The Dobsonian Telescope (1997, Willmann-Bell, Inc.).

Back to Top

Tip #4 - Using a de-focused star to accurately align your telescope to a star

An accurate star alignment of your telescope doesn't have to involve a cross-hair or illuminated reticle eyepiece. Instead, you can use an out-of-focus star with a medium power eyepiece. The first part of this technique is to locate a fairly bright star (magnitude 4 or brighter). Don't worry about getting the star exactly dead center just yet. Your image should look similar to this:

Next, you need to de-focus the star until the expanded star image almost completely fills the eyepiece. Then you simply move the scope so the "gap" between the expanded star and the edge of the field is the same. The image below is what you can expect to see with a Newtonian telescope (Dobsonian or Schmidt-Cassegrain).

If you're using a GoTo telescope or Digital Setting Circles (DSCs) you can set your alignment to the appropriate star using this technique. It's accurate and, more importantly, fast. Now you can focus and you're ready to begin viewing (or align to a second star if you're doing a 2-star alignment). Plus you don't have to buy a special eyepiece that you only use for alignment.

Back to Top

Tip #5 - Preventing inadvertent battery drain on a laser collimator

I have found that the Howie Glatter laser collimator I use has a tendency to engage the battery when the unit is stored in my accessories case. The first time I found that the battery was dead I thought I had forgotten to disengage the battery contact plug. After spending about $9 for a new battery I made certain that I disengaged the contact plug by at least three full rotations before storage. A couple of weeks later and I was out at a dark site with, you guessed it - a dead battery. My solution to this annoyance was to cut a 1/2 inch circle out of the top to a plastic container (sour cream, butter, etc.). Now, I place the plastic circle between the battery terminal and the contact plug before storing the collimator. Problem solved (and it only cost me $27 in batteries!).

Tip #6 - Using a large 12v portable fan to cool the primary mirror

Click on this picture or follow this link to see the fan I use to cool the primary mirror on my 25" Obsession telescope. Using this fan significantly reduces the amount of time required to cool the primary mirror close to ambient temperature.