Laser collimator for skywatcher skyliner 200P?

[Coastliner]

Thanks all, all posts read and digested - this is all good stuff and has pushed me further up the learning curve. I like the bit about the primary mirror essentially pivoting around the center spot.

Cheers,

Neil.

[Coastliner]

Also, I spent a while collimating last night (I understand it, but still find the primary adjustment fiddly to get it perfectly aligned) and agree that the star test can be difficult - the black dot in the defocussed star was central but the airey rings were difficult to perceive as the star was twinkling a lot due to the atmospherics.

[Jason D]

One common mistake with star collimation is defocusing the star little too much. If you see many rings and the diffraction pattern of the spider vanes are visible then you have defocused too much and the star collimation is no longer accurate. You need to defocus enough to see ~3 rings at high magnification. In addition, you need to evaluate only when the star is at the center of FOV.

Jason

[Scooot]

One common mistake with star collimation is defocusing the star little too much. If you see many rings and the diffraction pattern of the spider vanes are visible then you have defocused too much and the star collimation is no longer accurate. You need to defocus enough to see ~3 rings at high magnification. In addition, you need to evaluate only when the star is at the center of FOV.

Jason

Hi Jason, slightly off topic but others might be interested as well. Everyone try's to collimate to the coma free sweetspot at the centre of the primary. However as a Paracorr creates a much larger coma free area do you know whether being so accurate with the secondary would be so necessary if using a coma corrector? In other words if the laser dot was say, just missing the centre. It's something I've been wondering so I thought I'd ask you as you seem to be the person who'd know

[Jason D]

An interesting question.

A paracorr does increase the coma "free" zone; however, the focal plane of the paracorr needs to be as parallel as possible to the focal plane of the primary mirror. That implies the secondary mirror tilt adjustment is more critical when a paracorr is used -- kind of counter-intuitive.

In other words, you will not get the most out of your paracorr until you adjust the tilt of the secondary as accurately as possible. 

Jason