Barlowed laser collimation problem

[Dave In Vermont]

It's more off now from what I can see. Adjust the secondary to center the red dot in the doughnut, then check the laser to see if the primary needs a tweak.

Dave

[Charic]

The way the secondary is constructed is not an issue, you just need to ensure the mirror is round and central as viewed through the focuser.

When your adjusting, you need to be fairly accurate, but the adjustments are very small.  When you tighten something after adjustment, the tightening is enough to misalign the collimation. Try looking through the colli-cap without locking, does it look good?  then gently tighten the locks.  Are they still aligned, if not, that proves how easy it is to upset the system by further locking? Some folk leave out the lock nuts in favour of just a little tweak prior to observing. 1. saves  time 2. Doesn't upset the adjustment you have just made?

Generally, the secondary needs to be central  and concentric to the focuser axis,  then the secondary mirror  tilted to see the 3 primary mirror clips, then  the primary tilted to return the laser dot into the hole. Beyond this, there will be no further improvement once these parameters are reached.  Concentric Airy rings confirms the set-up.

If you reach the above standard, but  something still looks out of place, and your final image of a correctly focused Star looks good, then its not worth the effort to correct any further.

[Warped Drive]

I have redone it by sight and taking pics and using Al's collimation aid and I have it as near as be damed. Il will have to leave it there for tonight I have to head out to do some work in order to fund the big dob. Thanks every one for all the help

Ohh just looked out the window and the sky is starting to clear might get a bit of observing in after work if it stays clear.

[Warped Drive]

Managed to get the scope set up just in time for the clouds to start rolling in at about 2.00 am last night. I was able to line up on Vega and do a quick star test and it seems to be pretty good Al concentric rings, the secondary and the post it is mounted on seem very prominent in the image should that be the case.