Laser colimators

[deejayry]

I've had my newtonian for a few months now and have not made any atempt to colimate it so far, and visualy i dont see any signs of needing any adjustment at the moment. But i'm thinking it probably could do with being checked properly soon especially as i'm doing more imaging now.

I've seen plenty of guides that mention using a film canister with a hole in the center but i feel i would like somthing a bit more accurate so i'm thinking about laser colimators

Are there any laser colimators that are particulary good, any to avoid?

[RickJ]

At f/8 you don't need anything more precise than the film can. F/8 is very tollerant of errors that would kill you at say f/5. If you want something more precise a sight tube which is just a longer tube than a film can with a small hole at one end and crosshairs at the other can be built cheaply.

With a short focal length dob assembled in the field in the dark a laser is handy for the final tuneup of the mirror but that isn't your situation. If you are working at night a Cheshire type sight tube helps as it gives you a way to get light into the system to see what you are doing. It is all I need even with my f/5 scope but my f/4 does tweak faster, but nor more accurately, with a laser. Though I use the sight tube first to get close.

You can spend little or a lot for a laser unit. Expensive ones claim precise alignment an may use a barlow or other lens system. Maybe at f/3 it would help but its way beyond what you need at f/8.

If you just have to have one, one of Orion's rear view lasers would be a way to spend more money than you really need to. The cheaper $65 is overkill for your system but if there's a fast Dob in your future you'd be all set.
http://www.telescope.com/control/category/~category_id=scope_tune-up/~pcategory=accessories

I prefer a star test for really precise final alignment of a fast scope but use the laser when I'm rushed.

Rick

[deejayry]

Thanks for that info Rick, In that case i won't waste money on a laser one, The Celestron Cheshire Collimator is cheap enough, i guess one of those is more sensible.

[SanitysEdge]

http://www.telescope.com/control/product/~category_id=scope_tune-up/~pcategory=accessories/~product_id=05681;jsessionid=44BF0B883C9EA63DF26E6 D633DC08958.ivprod2
This one came with my SkyQuest XT8. I wouldn't recommend it. It sits too loosely in the focuser you don't get any sort of accuracy. The 10 cent collimation cap it came with works better.

[Tog_]

I sort of built my laser collimator. You need access to a metal lathe though. Basically it's a tube about 6 inches long that it sized to fit inside the focuser. In one end is a hole 1/64th inch in diameter and the other is sized to fit one of those 5 dollar laser pointers. There are three adjustment screws to center the pointer in the tube.

Once you get it in, you rotate the whole thing inside the focuser to be sure that the beam is actually centered. It's possible to have it be off by up to two inches. Rotating it in the focuser will make a circle on the primary if it's off center.

[Wakenaam]

If you have access to a lathe then diy a cheshire also - and if you do go to a laser then you may want to use 6 screws on the adjustment of the laser. I built both of mine and the laser is good to 0.5mm@20ft through the year (the beam diverges to a 15mm ellipse @ 20ft though .. :-)). Build yourself a 'V-Block' - even a simple design out of suitable wood that can be held stable on a work surface removes the focusser slop out of your alignment procedure.