Thanks for the advice Alistair and John,
Yes, sorry an f/5 12" dob (SW truss), but i'm also probably getting at an f/4 or f/5 8" for imaging.
Righto, so the Orion tube is also good but only comes in the 1.25" (i think). whereas the catseye package (i forgot to mention) has the 2" tube. So as long as the 8" newt i buy has a 2" focuser I should be alright.
John i think the extra $29 differentiates between two types of autocollimators that catseye offer (in addition to the cheshire).
it looks like you can choose options on what image it projects eg 'red triangle 3/16" or 'red triangle 1/4" 'does the size make much difference?
Thanks again
