If you look at
this thread you'll see that I have pmrid's F3.8 10" newt with a view to giving the beast a tune up while he's tramping around Europe. I've had quite a few newts and peter had a set of great collimation tools so I didn't think twice to help him out as he just got his MX mount and has his hands full with that. I've found that this thing is hard to get right, I'm getting it closer and closer but I still have problems and maybe you guys can help.
I'm sure the problem is the secondary alignment. It has a
prostar 3" secondary which has the focuser offsets built in. However I found that the 2 short legs of the spider where 2 mm different as well. I spent a lot of time getting the center bolt into the right spot, I have also center spotted the focuser however I had to alter the focuser tilt to get the secondary in the middle of the focuser sight tube which indicates to me something is screwed.
Doing a star test shows it is concentric inside focus but shows coma outside focus. This is giving funny star shapes. When aligning the secondary it always seems to have an apparent flat spot on the top left of the mirror. Does anyone have any tips on aligning the secondary? Should I center the focuser and move the secondary to suit instead of moving tilt on the focuser?
I also have reservations about using an mpcc at this F ratio. The info on opt says it's for newts from F4 to F6 with
visual users reporting good results down to F3.7. I have a qhy9 with wheel hanging off it.
Here's a set of lum on tuc 5sec subs and 253 120sec subs to see how close it is. Check out the big stars. and I had fast downloads on to avoid the clouds hence the vertical bars on tuc.