Help! Collimation woes.

[gb_astro]

Originally Posted by Renato1

Visually the telescope is great, and i mainly use a Nagler or Meade Ultrawide in it. The only difference is that I don't have diffraction spikes on stars from spider vanes, but instead have sort of a glow around stars from the arc vane.

The other odd thing is that I keep reading that if I use huge exit pupils, I should see the image of the secondary in the eyepiece. Yet with a 9mm exit pupil, I really have to strain to make out slight darkness in the centre of the image.
Cheers,
Renato

You said in post #17 above that you were seeing a doughnut shape, so the secondary must be showing itself there?

gb.

[Renato1 (Renato)]

Originally Posted by gb_astro

You said in post #17 above that you were seeing a doughnut shape, so the secondary must be showing itself there?

gb.

Yes, but all I am saying is despite all these books effectively saying huge exit pupils are useless in a dob because of supposedly having the secondary sticking out in the middle of the image, I find the huge exit pupils quite fine to use as I can barely detect the secondary.

The main advantage of huge exit pupils is that, as I have astigmatism, I twist my eye at the correct angle and the astigmatic flare on stars disappear, without blanking out part of the image - as would have been the case with a smaller exit pupil eyepiece.

I like using a 40mm 2" Konig with a Skyglow filter in my f/4.5 dob to just sweep across the Milky Way. It is quite dizzying some times.
Cheers,
Renato

[CJ (Chris)]

Fixed it!
Something not mentioned in some articles and videos was tweaking the secondary until the collimator laser hit the primary centre mark.
I removed the primary to check the clamps which seem ok. The carrier did indeed have a recess to accommodate the tube seam but I had marked the tube for relocating so that probably wasn't the problem. I then used the laser to adjust the secondary and then the primary. Finally got a clear night last night and hey presto, the collimation was good. Not perfect but very acceptable. Phew!
Thanks for all the comments. I've learn't quite a bit.