Monday, 19 May 2008


During my last observing session with the 12-inch, the collimation was way off, so I was only able to use low powers which is a pain in the arse when you want a closer look at something. I couldn't suss out the laser collimator I got (it came without instructions - how stupid is that?!) although centering the beam on the primary helped a bit (but do not look down the tube to see where it is before holding a piece of paper in front of the scope to see where the return beam falls if it misses the secondary- if the beam is off, you might get an eyefull of laser and you certainly don't want that!).

However, after posting on Cloudy Nights I found out that centering the beam in the primary is not enough because that means that only the secondary is aligned. Once the beam is in the centre of the primary, you then have to adjust the screws on the primary so the laser return beam is centred on the hole in the centre of the view port on the laser - it will look like a tiny eclipse.
There is a super video on a website called Andy's Shot Glass and this is the best, most instructive tutorial on collimation anywhere I think: collimation video

The laser is great because that eliminates the need for a second person to twiddle the knobs while you look down the eyepiece. If you keep the laser view port facing the back of the scope you can see where the collimation is at and twiddle the knobs. Afterwards you can see what the mirrors look like with a collimation eyepiece (I made one from an old film canister I found in a drawer).

I am hoping for a clear night tonight so I can try it out, so it's full Moon, but that doesn't matter.