New - see section on astrophotographic collimation of newtonians below:
Suffice to say, the basic principles that you need to learn about are as follows
1. Square the focuser with the OTA.
2. Square the secondary in the focuser.
3. Align the secondary with the centre of the primary.
4. Adjust the primary.
There. Simple. :-) Seriously, go and read around.
The idea is to remove the inaccuracies of the wiggling laser collimator by transforming the laser from a coherent beam of light to a light source placed an infinite distance away. Or something like that. Anyhow, read on, it works.
This removes the wiggle factor from the equation.
1. Do a normal collimation of your telescope.
2. Find a barlow. I have a 1000mm focal length Newtonian telescope, and get on best with a 2x barlow, but you might want to experiment.
3. Make a mask. This needs to be a little circle of paper or card with a 2mm hole in that is secured over the telescope facing side of the barlow. Personally, I have a barlow I never use, so employ some bluetak and a dremel cutting disc.
4. Put the laser into the barlow where you would normally put eyepiece. Now, look down the OTA. You will see a circle of light on the primary mirror, roughly over the centre mark. If its not over the mark, wiggle your barlow a bit.
5. Now find a small mirror. I use a CD. Something by Pink Floyd works well. Something you can fit into the top of the OTA without touching the sides or the secondary. The idea is to try and view the face of the paper/cutting disk mask that is hidden up the focuser.
6. This mask has the reflected blob of light on it. Look very carefully and you will see the shadow of the primary centre marker.
7. Now adjust the primary mirror so that the dark ring is centred on the hole in the mask. This will involve either an assistant, or a lot of running back and forth. Or rig up a webcam, or something.
8. Now the magic bit. Whilst looking in your mini mirror at the centre marker shadow neatly centred on your mask hole, reach around with your third hand and wiggle the laser/barlow/eyepeice holder assembly. You'll see the blob of light move, but the ring of shadow from the primary centre marker remains steady! Clever, eh?
Note: You might not need the hand mirror, with some setups you can see everything you need by looking in the primary and seeing the donut relfected in the secondary.
The really elegant part being you have made the CCD perpendicular to the axis that light normally enters the camera. Not level to the box, or lid or whatever. Its lined up to that optical axis you have been struggling to get collimated for the last dozen paragraphs.
This is a great place for collimation information
At first glance newtonian telescopes appear fantastic for astrophotography. Lots of inchs of aperture for not very much money. The reason they are not perfect is that compared to expensive refractors they do not have a large illuminated field. Also, they exhibit off-axis coma. The coma is inherent in the optical design of fast newtonians, and gets worse the faster they are. To understand how factors such as secondary size effect these things look at this spreadsheet.
The point I am trying to make is that on most newtonians the "sweet spot" with good illumination and low coma is very small. Which means that you need to make sure the light cone is collimated to hit the ccd chip squarely.
It is my opinion the part of the collimation that effects this most is adjusting the secondary so that is is centred when you look down the focuser. The secondary rotates in it's holder. If the secondary is not rotated so that is it pointing direcly square with the focuser, the light cone will miss the centre of the ccd. Most collimation instructions skim over this section, telling you something about making it look centred when you look down the focuser. I think this is very hard to do.
This first thing to do is make sure the secondary hangs down the tube the correct amount. Use a ruler to mesure the distance from the top of the OTA to the centre line of the focuser, and make sure that the centre of the secondary is at about the same position.
Next, look at the secondary holder. Usually they have three screws for adjusting the tilt of the secondary 120 degrees appart. You must make sure the spider that holds the secondary is correctly fitted. You should have one screw pointing at the focuser side of the tube.
Now, the key is to rotate the secondary into position, and only use the front screw (nearest the focuser) to adjust the tilt. First make sure that the 3 screws are extended the same amount. Then put the laser into the eyepeice holder. The red spot will point somewhere onto the mirror. Slacken the three screws so that they just hold the secondary in position, and rotate the secondary so that the laser spot falls on an imaginary line between the primary centre spot and the wall of the ota in line with the focuser.
Now adjust the tilt of the secondary so that the laser spot hits the primary centre spot. You must tighten and loosen either the focuser side screw on its own, or, the two other screws together. If the spot moves off the imaginary line on the primary, do not use the back two screws to tilt the secondary, you must rotate the secondary until the laser spot is back on line, and then try to work the laser back onto the centre spot again using either the focuser side screw or the other two together. Once the laser spot reaches the primary centre mark, your secondary is correctly aligned, and you can carry on normally with tweaking the primary.