Note: I also made a tutorial how to collimate my LX200 SCT telescope
When I compared my astro images with those captured by others while using comparable telescopes I began to fear that something was wrong with the collimation of my TAL-2M.
So I captured a star-out-of-focus image and submitted it to the QCUIAG community.
I know the image below lacks lots of quality, but it clearly shows that I did not have the required perfectly round "do-nut" image I had seen at Thierry Legault's site.
You can see the diffraction rings, the 4 spider vanes and the dents of the 3 clips holding my primary mirror
... and there is always room for improvement ...
But now back to the beginning of my collimation story ....
The response of the QCUIAG community was: I had to collimate my Newtonian telescope.
So here I was: scared to approach the delicate optics of my telescope with a screwdriver. Several people encouraged me and pushed me over the threshold.
Then came a more difficult step: I had to put a marker in the exact centre of the primary mirror. I had read over and over again to be extremely careful with the mirror: fingerprints, scratches etc.
I wonder why manufacturers of Newtonians don't put such a marker there already ?? Strange ...
I took my primary mirror from the tube and used a sheet of white paper to cut that to the precise diameter of the primary mirror. Now I had a square piece of paper. I folded it to get the exact centre = the exact centre of the mirror. I put a self adhesive notebook reinforcement ring - from the bookshop - at the centre of the paper. Next I carefully cut out the ring, so now I had a square piece of paper with a centred hole matching the size of the ring. Gently I put the paper at the mirror and inserted a new self adhesive ring in the hole = the centre of the primary mirror. I took care not to touch the mirror through the hole of the ring, as laser collimators use that spot (!) I removed the paper and now I have a mirror with a ring in the centre.
Note: I did NOT use a pen to mark the centre of the primary mirror as all the guidelines told me, but that I used the sheet of paper as a mask instead. My main reason is that I read somewhere that laser collimators use the centre of the primary mirror, so if you put ink there I assume that would not be a good idea.
Look HERE (you have to scroll down a bit once you are there) to see the ring on my primary mirror.
I re-installed the mirror in my OTA; the other end of the OTA I covered with a sheet of white paper. I illuminated this paper with a bright light, giving a nice diffuse but yet clear light inside the OTA.
I peered through my collimation tool (the canister with the hole) and I adjusted the primary mirror in such a way, that all spider vanes were more or less of the same length. I did this by using the controls - in very small steps - at the back of the mirror. I stopped when I was satisfied that all spider vanes were equally long now.
I looked again through my collimation tool and with some difficulty could see the notebook reinforcement ring. However, this ring (at the centre of the primary mirror) was not yet in the centre of the secondary mirror. So I adjusted the primary mirror a bit more and presto: there my ring was right in the centre of the secondary mirror. I was pleased to see that now the lengths of the spider vanes were even better matched than they were before.
Next I turned the focuser up and down while peering through the hole: the ring stayed nicely in the centre. Now I was satisfied and could not do anything else. The waiting for a clear sky began: the ultimate test.
That night there were quite some clouds but also a lot of stars and Saturn and Jupiter were visible once in a while.
I did a star test of course WITH my camera mounted and me looking at the screen with and without my new 2x Vixen HQ Barlow (and also the 4x Barlow). Result: I saw nice concentric rings and perfect donuts, like straight out of the textbook. So I am happy. And my images show that I have improved.
I am sure a lot more can be told about laser collimators and what have you, but all I wanted to do is to write down in a step by step manner how I overcame my fear to collimate ....
Some remarks (thank you Cor Berrevoets!):
The top row (#1 through #4) are overexposed, but the white dot in the centre is showing nicely: a sign of good collimation.
#6 has most information: the inner and outer rings are equally well exposed and the inside diffraction ring shows the same characteristics: with imperfect collimation the light balance usually is distorted.
Real life raw screen print of my collimation (of course I use my webcam when collimating: easier to see what I am doing).
September 14, 2003.
You can see the 4 spider vanes and the 3 clamps that gently hold the mirror.
The horizontal lines are caused by noise of the camera.
November 13, 2003.
I bought a laser collimator to ensure that I really got the most from my scope.
In spite of all my previous collimation efforts I was amazed to see that the secondary mirror was way off, as the laser showed me.
I bought this laser here: Teleskop Service - München.
And here is more about Laser Collimators
This commercial - but realistic - images shows how to check and improve the collimation of the secondary mirror.
The goal is - while looking into the tube - to move the red laser dot to the centre of the primary mirror.
This realistic image shows the collimation of the primary mirror: the red laser dot should be right in the centre.
And here is more about Laser Collimators
Andy Raiford: very useful animation with sound