laser collimator for collimating SCT?

[Astroblagger]

Hello just wandered what your thoughts were on using a laser collimator to collimate an sct? or is it better just using a star?

[cgarry]

You have to use a star in the first place either way. In theory a laser collimator can get you back to a known collimated state but will not help with the initial collimation.

Personally I would say a laser collimator is a waste of money for an SCT.

Cheers,

Chris

[Dave]

You have to use a star in the first place either way. In theory a laser collimator can get you back to a known collimated state but will not help with the initial collimation.

Personally I would say a laser collimator is a waste of money for an SCT.

Cheers,

Chris

I second that.

Dave

[StevieDvd]

Unless I've got it all wrong you use a laser collimator on an SCT to record the correct alignment so you can bring it back to that setting if it gets changed. Not sure you can use a laser collimator to put a badly aligned SCT back to optimum without the original settings.

I recently added Bob's knobs to my SCT and recorded the setting and made sure it was the same after the knobs were replaced. A star test showed it was collimated OK but I need a longer session to fine tune it.

There is a thread around here somewhere that discusses aligning an SCT visually too.

No doubt someone can confirm/clarify or correct any of my understanding.

Note I was typing this out before I saw that others had already replied - must type quicker

[Peter Drew]

It shouldn't be necessary to use a laser to visually get close to good collimation on a SCT. The only component that is adjustable is the secondary. If you place some form of collicap into the eyepiece holder and look through at the secondary you can immediately see if there is a substantial error. The secondary mirror has an external baffle that appears as a black ring round it, if the secondary is out of collimation then this ring will appear thin on one side and thick on the other. If you adjust the secondary until this ring appears concentric the collimation is pretty close and suitable for fine tuning on a star. Two things can help to make this initial process a 5 minute job, Bob's Knobs and an assistant to look through the collicap to tell you which way to progress.