SCT Collimation

[Kai]

Do you collimate with a diagonal on or Off ???

If you collimate straight through for a Ccd for example would it affect collimation when you added a diagonal for viewing.

Cheers

[mike bacanin]

This is a question i asked on cloudynights a little while back.

it seemed a good idea to collimate for visual use with the diagonal in place, unless of course you collimate without and then adding your diagonal shows no difference at all.

when i was at telescopehouse last weds having my tak sct corrector cleaned, the scope was collimated without and then we added a TV everbrite 2 inch diagonal.

the everbrite had no effect at all indicating it itself was spot on collimated.

this may not be the case with others, so best thing is collimate without and then see if adding the diagonal causes a change. if it does, recollimate with it in place for visual use.

in particular with an sct, any error introduced by a diagonal will affect the image quality.

mike

[MartinB]

Best to do it without for imaging I think Steve. However, the better the seeing the easier it is to collimate so you need to use a high star. This can make things uncomfortable to say the least. A more comfortable collimation may be a better collimation!

I now use an artificial star. Can then collimate with the scope at a comfortable angle on a cloudy night. You need to be able to get the star a good distance away from the scope though

[mike bacanin]

i would agree with martin, collimate without for imaging.

when you add the diagonal for visual, its down to the quality of the diagonal's collimation.

you will tell by what it does to the out of focus star.

mike

[Kai]

So if its for visual then ,if i collimate with the diagonal in then i would compensate for the diagonal if it was mis-aligned

True ????

[zero]

You should always collimate an SCT straight. Diagonals are rarely 'in' unless you have an Everbrite. Making the scope compensate for a poor diagonal just lets everything down a peg. The diagional's not going to make a huge difference if it's a tad out, whereas if the scope's out you'll see it a mile off.