More questions on colimation (/seeing?)

[Solanum]

But specific at least....

Firstly, I think I have things lined up fairly well, the secondary is roughly in the centre of the focusser, the primary is fully visible (roughly in the centre of the secondary) and using a Cheshire eyepiece the circle on the centre of the primary is dead on the central dot viewable through the Cheshire. However, In the reflection of the secondary I can see the edge of the focusser that faces into the tube and it's not central in the secondary reflection. I can see the whole of the focusser edge though. Does it matter and what is slightly out?

Secondly, when viewing a star at high magnification it has always looked like the atmospheric turbulence example here: http://www.skywatchertelescope.net/EducationST.html
(bearing in mind that the scope is new and I've only used it maybe 8 -10 times so far). I've never seen the 'airy disc'. I had assumed that it was limitations of the scope, but now I'm guessing it is the 'seeing'. Where I live we have beautiful dark skies, but the diurnal temperature range is very rarely less than 15 deg C, often more (even in winter). Am I really suffering from atmospheric turbulence? Will it always be so with the diurnal temp range? What time of night is the best seeing?

[Geoff45]

Things should look like this. Look here http://web.telia.com/~u41105032/kolli/kolli.html for the full and very good article.
Geoff

[rmcpb]

To ensure the secondary is centred I use some graph paper as the background. When viewed through the Cheshire, which ensures your eye is centred, you can then count the squares in the FOV on each side of the secondary and then know it is centred.

As for the best views due to seeing, after midnight would be a good rule of thumb as the atmosphere has had time to settle but not very convenient. I often leave my scope out on a covered deck overnight and take it out about 3am for the best views. Early start to the day but great views.

[Solanum]

Thanks for the replies, the secondary seems to be pretty much centred, and the view is approximately like the diagram. Looking at that diagram, within the reflection of the secondary I can see the circular edge of the focusser (facing into the tube) and it is that that is off centre, everything else seems centred as in the diagram. The centre spots are over the top of each other.

I guess, it must be, as Rob suggested, that despite appearing to be centred in the focusser, the secondary must be a little high up the tube. But as everything is lined up, does it matter? If the optical axes are lined up together but a mm or two off the centre of the secondary, will it make much difference? I will try Rob's suggestion with the graph paper next time and check.

I can likewise leave my scope out under the veranda to keep at ambient temp - haven't got up that early yet though, having a 3 month baby and 3 year old twins means every moment of sleep is precious!

Ev

[rmcpb]

Just think of the need for some peace and tranquility in your life with the kids and a 3am rise every now and then is not so hard :)

Besides, Jupiter is fantastic in the early morning at present.

[iceman]

Except this morning, the seeing was rubbish! :bashcomp:

[rmcpb]

Yeh, BUT Saturn and Luna were brilliant last night about 10pm :)

[Sausageman]

Ev
I recently bought a book from Bintel entitled "Introduction to webcam astrophotography" by Robert Reeves. ($69).
It has some very interesting content on collimation on different types of telescopes, easy to follow instructions, and much more on focussing techniques.
It also has a wealth of knowledge on other subjects, not only imaging, such as working out the real focal length, not the one stated in the manual.
This book is a must for any astronomer.

My knowledge has increased a thousandfold, from idiot,:shrug: to almost competant,:whistle: and I'm only half way through the book.:thumbsup:

Mike.

[RAJAH235]

Another good link..>
http://skytonight.com/howto/diy/3306996.html