I have been observing with an uncollimated scope!

[§AB]

In preparation for tonight's session, I decided to try and address an issue with my 12" dob that has been bugging me for a while. WHen I rack the focuser in and out, the center spot of the primary moves relative to the cheshire dot. Also, the secondary didn't seem to be centered under the focuser.

I decided to tackle this, but after doing everything humanely possible to the secondary, the cheshire dot movement still occured when I racked the focuser. I figured I might need to shim the focuser.....so I jammed some tiny squares of paper between the focuser base and the UTA and VOILA the shift has gone! Also, the secondary appears much better positioned under the focuser

Just now after an hour cooling, I nervously popped my 8mm LVW into the focuser and aimed at Jupiter. Wow there was immediate increase in detail! Even though the mirror is nowehere near equilibruim and the seeing seems terrible at the moment (massive flaring and even double images of the moons), I could see festoons and detail in both the nEB and SEB which were never as obvious before

[Starkler (Geoff)]

I take it you have a sight tube with crosshairs at the end?

If you align the secondary by placing the crosshairs over the primary centre spot this will align the focuser axis to the optical axis, and there shouldn't be any shift.

[TrevorW]

Obviously not enough use !!!

[§AB]

Originally Posted by Starkler

I take it you have a sight tube with crosshairs at the end?

No, it's a tectron cheshire.

If you align the secondary by placing the crosshairs over the primary centre spot this will align the focuser axis to the optical axis, and there shouldn't be any shift.

thanks for the tip, but the sight tube flops around in the focuser too much to be of use.

I've got it sorted now, the focuser needed shimming to get the secondary properly centered (couldn't before) and now the shift I mentioned is eliminated. The collimation didn't move one bit during an all nighter session.