Dan wrote in another thread:
Chuck Hards brought up one in that lasers themselves need to be in collimation to be of value. A common reply to this problem is to "buy a really expensive one" and that will solve the problem. A better approach is to set the laser in a pair of v blocks on a sturdy table, aim it at a wall that's the focal length of your telescope away from the laser, roll the laser around in the v blocks and measure the radius of the circle the dot traces on the wall, if it's more than millimeter the laser is defective.
Absolutely. The low-end collimators that I bought and have see, like this $60 Zhumell model were worthless even with bench alignment. http://www.opticsplanet.net/zhumell-laser-collimator.html The tool would not hold an alignment. Even by the time you do get the laser aligned, the battery runs down. Then you have to pull the laser to replace the battery - which means unscrewing the three laser alignment screws. So, you are back to square one. Or worse, the battery runs down such that it looks okay on the bench, but when you get to the field, it dims while you are collimating the scope. Then when you put the collimator into a 1 1/4" adapter, it isn't machined to the right diameter. The result is for a low-end collimator - and here's the acid test - as you rotate the aligned laser collimator in the focuser adapter through 360 degrees - the laser dot does not trace a 50mm circle on your primary mirror. With the Glatter style lasers - which are admittedly are much more expensive - come well machined and with rubber corking to center the collimator in the focuser adapter. The result is that the collimator consistently traces a 0-1mm oval in the center of the primary. (The balance of the movement error is in my mid-range Moonlight focuser and 1 1/4" focuser adapter.) The battery pulls out the back without effecting collimator alignment. My recommendation for not trying to save by going with the low-end collimator is simply time. With a high-end collimator on a fast-Newt, I can consistently maintain and set right-on collimation in under five minutes. No mess, no fuss, no questions. Based on my experience, going with the low end collimator to lower expense is just not worth the time lost to futzing with a poor tool.
The subject tends to generate a lot of heat and smoke with very little illumination when it comes up on Internet discussion groups.
Definitely want to avoid that here. - Kurt ____________________________________________________________________________________ Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now. http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ