Home made Laser CollimatorBased on Nils Olof Carlin's excellent design found at http://w1.411.telia.com/~u41105032/kolli/kolli2.htm#mklaser
Some design differences:
The project costs about $20 and about 4 or 5 hours. It's not that acurate, but I think it's definitely good enough to bring things to the point where all that's needed is star collimation. I could be wrong, but if seeing isn't good enough to star-collimate, then you probably won't be able to tell the difference anyway. The inner tube is a 4 inch long, 1 inch outer diameter piece of pvc pipe. The outside tube is also 4 inches long, and (almost) 1 1/4 inch outer diameter plastic sheath used for lamps (picked up two of them at Home Depot near the electrical isle for 79 cents or something). Other materials are a cheap laser pointer keychain, 6 screws, one large thumb screw, electrical tape, and a plastic or cardboard disk with a hole perfectly in the center, and cut to fit the inside of the 1 1/4 tube. The electrical tape is just used to make the tubes wider. The inner tube has several layers so that the outer tube fits it well, and the outer tube has about one and a half turns so that it fits the focuser well. The disk in the middle serves two purposes: narrow the laser beam (the cheap laer pointer I got had a funny oval shaped beam and was very wide) and give a target for the return beam to reflect off of. Mine is just a piece of 3x5 card that I used a compas to cut to a perfect circle with a hole in the middle, colored with a black magic marker, and hot glued in. I'll probably pull it out and make one out of plastic instead (a film canister bottom, for instance). The hole in the disk should be very small. A laser beam is potent and should be easy to see even if just coming through a pin hole under a millimeter, but widen it to your liking. Finally, use a hobby knife to cut out a window in the outer tube so you can see the laser beam returning. A variation would be to put the disk in at an angle (it would actually have to be an ellipse if you do this), much like a cheshire, making it easier to see the return beam. I'll probably do that when I replace the cardboard with plastic. But that's laser collimator 2.0...
To callibrate it, first center the output side of the laser in the front screws, then use the rear screws to aim the beam so that it shoots straight. As Nils' guide suggests, you can put it in an L shaped structure (two books layed down in an L shape, for instance) and rotate it. When it no longer traces a circle on a wall across the room as you rotate it, it's centered. As a couple final notes, be very acurate about all your work. If a millimeter error can throw things off in a collimation, a millimeter error in the collimator design can do just as much damage. When you turn it on using the thumb screw, only turn the screw just enough to turn the laser on. Tightening it too much can damage the laser pointer, but also it can throw off the alignment by bending the laser pointer's body and angling the beam away from center. Also, with that in mind, you should probably check the alignment of the laser (with the L-shape method) very often. Such is the hidden cost of a $20 laser collimator. To use it, first center your secondary via a site tube, site tube with crosshairs, or just a simple peep hole cap, whatever. This usually isn't necessary unless your scope is very out of whack. Once that's done, adjust the tilt of the secondary so that the laser beam is dead center of the primary. Finally, adjust the tilt of the primary untill the beam doubles back on itself and reflects right back to the hole it comes out of in the collimator. This is why we cut the window in the tube. Speaking of the window, don't make it too big, or the tube will be too weak and may bend under light stress (which will again throw off the centering of the beam). Ordinarily, I have enough confidence in what I say that I won't put a disclaimer, but in this case, I'd like to ask readers to look at other websites too. I only learned how to collimate a couple weeks ago and though I think I have a good idea of how it works, I have to warn you that there may be something I missed. You shouldn't trust everything you read on the internet anyway. Except for those pyramid schemes. They really do work. Honest. ;) As they say, clear skies!
Updated April, 2003 |
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