Telescope Reviews: Catseye vs. Howie Glatter and Blug??

John,
We've communicated before about a few possible mods that could eliminate any movement that results from design-related issues, so I will just make some notes about the tools used and collimation. Glatter does not make an autocollimator.

Step 1: Center the secondary under the focuser and make it round by rotating the oval until it appears round. This is typically done once, and not again until the mirror is removed for cleaning. The tool to use is a sight tube, or, if you can hold your head steady enough, the focuser by backing your head away a few feet until you see the inside diameter of the focuser *just* larger than the outline of the reflective surface of the secondary. When these are concentric, you're done here.
Step 2: using a single beam laser, or a sight tube, angle the secondary to put the beam in the center of the primary (laser) or the centermark behind the crosshairs (sight tube). Go back to step one to see if the secondary moved. If so, repeat step one and step two as many times as necessary until both agree at the same time.
Step 3: using a barlowed laser (or a Blug), or a cheshire, or a Krupa collimator, align the primary to the optical axis. If the movement was more than a tiny bit, repeat step two to see if there is any movement. If so, repeat step two and three again until both agree at the same time.

To all intents and purposes, you can stop here. When all steps agree, then the return beam of the single beam laser should return to its source. You don't use this to collimate originally because there are many tilt solutions for the secondary and primary that can return the beam to its source that are not correct collimation, but once the scope is collimated, the return beam should return to its source.

At this point, if the laser wanders on the primary mirror when the scope moves up and down, something somewhere is moving. It could be flex in the truss poles, but more likely it is elsewhere--the screws, the spider tightness, the focuser, etc.
But, no matter where it is, it can be tracked down and, if not eliminated, tamed to insignificance.

The autocollimator, at this point, can be used to collimate even more exactly. Some would argue that it's not necessary. Probably true, since, if the previous steps all show good agreement to your ability to discern the details, you are probably within tolerances. But if you want to collimate more exactly, the autocollimator can do so. If it shows no errors at all, it was the final arbiter of collimation. But, more likely, it will show that a further accuracy is possible.

But say you see no collimation movement with the earlier steps. Does that mean you will not see collimation movement with the AC? No. It is incredibly sensitive, displaying changes with movement in the low thousandths of an inch. You can be assured that if you see no movement in the AC with altitude change, there is none to speak of.

If, at a future date, you decide to get a Paracorr to eliminate coma, then you should definitely invest in an autocollimator. Until then, just be careful with steps 1-3 and I think you'll be fine.

If there are some design issues in GSO scopes that result in collimation changes with altitude, but are easily fixed by $0.50 of parts from Home Depot, I don't regard that as a design flaw. It's probably due to an economy in manufacturing. No big deal.