Collimation tip

[acey]

For collimating my 12" flextube I always use a laser for the secondary and cheshire for primary. The other night I had my first session for a couple of months and the scope was way out. I collimated as usual but found that although the dot and ring coincided as I looked through the cheshire, the cross-hairs didn't align. Suspecting that some rotation of the secondary was at fault, I rechecked the secondary with the laser, and sure enough, the secondary was now out - because I'd moved the primary so much. So I realigned the secondary, getting the laser dot inside the primary ring, and of course now the primary was out, when viewed with the cheshire. And once the primary was sorted, the secondary was off...

But it was getting closer with each iteration, so I just repeated the same procedure three or four times, until I got perfect collimation. If I'd been in daylight then I could have got the secondary rotated well enough straight off. As it was, I managed the whole thing in darkness (with a red light to illuminate the cheshire) with a bit of patience.

Haven't had to do it before so just thought I'd pass this on as a tip.

[Bart]

acey,

wow, did you get any observing in after all that?

[acey]

Took about 20 minutes while the moon was setting, then I did 3 hours observing until clouds rolled in at 3a.m. - it was a great night and I was glad I took a bit of time to get things right at the start.