Very often, I have seen people using lasers to collimate the above mentioned scopes. Assuming you know that the laser must be well aligned first and you know how to collimate using a laser, is that really good enough?
What happen to the following tool? I have not seen a single person in singastro using this :
The above is the Cheshire eyepiece with a cross hair.
You may think that having your laser hit the centre of the primary and adjusting the primary to hit the opening of the laser means your collimation is good enough. Is that really true?
The problem with laser is that you cannot determine if your secondary is correctly placed. How do you know if your secondary is squared with the focuser? And how do you know if your secondary is offseted correctly?
Scope performance is often robbed not because of collimation, but because of a poorly placed secondary. While your alignment of the primary may be dead on, a poorly placed secondary will waste those precious light, giving you sharp, but dimmer than what your scope should give.
The right way to collimate is to use the cheshire to check the secondary position first. Many people never do this step. They jumped straight to laser. Once the secondary position is corrected, you can then use the laser to check for the primary. Actually, the Cheshire hire eyepiece can do everything and is even more accurate than a laser, albeit less convenient especially when you are doing this at night.
The good news is that normally once you got the secondary in the right place, the secondary should hold that position quite well. But it always good to check that first before every observing session.
For those using refractors, the cheshire is a wonderful piece of instrument to check for collimation. You can't go wrong with it. With lasers, you have to make sure that the laser output is aligned and that you have to decide for yourself if that laser is coming out at the centre of the objective lens. It's quite a subjective thing. And how to do avoid parallax error when you can't look straight at the lens? (there is laser there...dun look straight at it).
The Cheshire can also check collimation in diagonals. It cost half the price of a laser, and is totally maintenance free.
It's time that you guys should take a good look at this under-rated and under utilise piece of instrument.
"The universe is composed mainly of hydrogen and ignorance." 
. anyway, thanks for the suggestion.
