Collimation

[mattyb217]

I was just wondering when should you collimate a telescope, will I be able to tell if it needs doing or is it just done on a regular basis

[guggle]

Do you pack your scope away when you've finished using it, or does it stay on its stand in the same place?

If, like me, you do the former, then ideally you would collimate regularly - some would even say every time you set up. If its the latter, then it needn't be done as regular.

[OzStarGazer]

The manual for my scope has an image similar to the one below to test if it needs collimation (you test it on a star):
http://www.ellenrooneydesign.com/gsproduction/sites/default/files/images/Star%20test2.jpg (the upper image means it is not collimated when it is out of focus; the other one means it is collimated if the circles are concentric when the star is out of focus).

[mattyb217]

I only move it in & out of the house, when it's not being used I leave it set up in the study, when I am using it I just move it to the backyard.

However I did just take it away with me over the long weekend (to a dark sky area. It was FANTASTIC!) when traveling in the car I put it in the styrene holder it came in when I bought it, so it's secure when in transit.

[guggle]

It's probably worthwhile checking after moving it, particularly to and from your car.

[barx1963]

What sort of scope are we talking about BTW?
As a rule I always check collimation before any session and quite often during sessions. My scope hold collimation pretty well but as temp changes and it is being moved around the sky it will sometimes need a tweak.
Smaller scopes, eg an 8" dob, probably don't need as much checking, but it is still a good habit to get into and the more you do it the quicker it becomes.

Malcolm

[Amaranthus]

SCTs generally require less regular collimation than reflectors, but it's usually worth checking it every few sessions. Doesn't take long to check, or fix.

[mattyb217]

It's an 8" dob

[barx1963]

Smaller scopes like an 8" dob are much more tolerant simply because the components that are likely to move are much lighter (eg the primary mirror) so are held in place more easily. Also usually they are f6 which makes it a more tolerant scope anyway.
Still I think regular collimation is a good habit to get into, once learnt it is very quick and painless and if aperture fever hits and a bigger scope arrives it will be second nature.

Malcolm

[mattyb217]

Well I got to check for collimation last night, going by the image in the diagram it doesn't need doing though I will take Malcolm's advice & get in the habit of just doing it. Thank everyone for the help

[barx1963]

Just be aware of couple of things with a star test. The image shown is pretty idealised in that it represents the view in perfect seeing. An unsteady atmosphere (which is most of the time) will make the rings jump around. It is still doable, just be aware of the fact. Also use a high power eyepiece and moderately bright star, 2nd or 3rd mag is often best I have found, and try for one high in the sky to minimise the atmospheric effects.

Malcolm

[billdan]

Question on star testing, how can you tell from the star image which mirror (primary or secondary) to adjust? Or is it trial and error.

Most star testing articles I've read uses SCT's and they only have one adjustable mirror.

Cheers