OK an other Collimation issue

[John Mckay]

Hi guys, i have a 10" Sky-Watcher Dob, you have given me lots of great advice in the past. I tried my first REAL Collimation tonite.

No matter how hard i try i can-not!! get the primary mirror clips in the view when playing with the secondary. I have been using Astro Babys guide and it is fantastic, but think i may be doing somthing wrong , my scope seems to have more than three clips??

I use a Cheshire only as dont have a coll cap and have done my best, when looking down the Cheshire now, and after messing with the primary all looks central-ish except at the right of the view there is a dark thin crescent. Is this wrong?

[sixela]

If you can't see the clips no matter what you do you should rack the focuser in some more.

'At "the" right of "the" view "there" is a dark crescent' isn't precise enough for anyone to comment.

Have a look at some other collimation threads for Jason Khadder's diagrmas and pictures and compare, and tell us exactly *what* is different, possibly by annotating the diagrams.

[Neil McRae]

John I did my first collimation 2 days ago using Astro Babys instructions and had a similar problem on my SW 200P. The way I "got around the problem" was tp crank the focus tube fully in and then see that by moving my eye around I could see all 3 clips were relatively central. The rest of the collimation went perfectly and I ended up with images exactly as those in the article. Now waiting for cloudless night to see the reults. Hope this may help but please if this is not correct someone tell me

Neil

[Astro_Baby]

The 250 has more clips but its the same process. Get all the clips in view and at the same distance round the secondary mirror image. You may need a colli cap to pull this off - my own Chesire wont do this as it presents too narrow a field of view which is whay I use a colicap for that part of the alignment. You will also have to rack the focuser in/out etc to get the best view and you may need to be swivelling your eye. I have a 250 which is hoplessly out of collimation which I have to get round to doing soon.