Telescope Reviews: Three screw adjustment hint

Most of you know this hint by now, but it took me about a year to figure out, so I thought I'd share it. There are a lot of three-screw adjustments in astro equipment, such as primary and secondary collimation, laser collimator adjusment, and finder brackets. For a long time I found this very difficult. Until I figured out this simple protocol.

Suppose you're using a laser to collimate the primary (the same method should work for all the other three-screw situations). You want to move the return beam spot to the center. You go through all the collimation screws one by one. You can move the screw a bit in any direction to observe the line along which the screw moves the laser spot, and then turn the screw until the spot is on the point of the line closest to the center. Then go on to the next screw. If one's lucky, then after having done all three screws, one will be close enough. If not, one just continues the process. At each step one gets closer, so there is constant progress.

This is so obvious that I'm a bit embarrassed to post it. But I tell my students that if they don't understand something, probably they're not alone, and they should ask a question in class. So, I'm guessing that if it took me a long time to figure this out, some others might benefit. :-)

I think there were three reasons it took me a long time to figure out:

1. The whole business of moving along three non-perpendicular axes is innately confusing for those of us with a habit of thinking in Cartesian coordinates.

2. The confusion was increased by the fact that my collimator doesn't project a spot but a cross, which makes one want to align along the cross's axes, instead of just making the cross's center go to the right place.

3. I often haphazardly tried to guess: "Which screw do I need to turn to fix this?" The amount of time spent trying to guess is wasted (unless one has enough experience with the particular scope that one can just see it right away). Instead, one just systematically optimizes each screw in turn (say, going clockwise around). (Actually, I sometimes still do the haphazard guessing, because I am too lazy to go systematically around.)

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Coulter Odyssey 13.1" split-tube
Coulter Odyssey 8"
Home-made 7.8" F/4 dobsonian travel scope
Home-made 68mm F/5.3 achro (typically used as finder on 13.1")
Skymaster 15x70
BPTs4 8x30
32mm Plossl, 30mm Rini, 27mm Kellner, 13mm Hyperion, 6mm TMB/BO Planetary, Owl 2X Barlow
Palm TX with AstroInfo and RescoViewer