Collimation (Yes, ANOTHER collimation thread!)

[lw24]

Hi, i've been recently looking around for a telescope, and have settled for the Skywatcher Skyliner 150p Dobsonian (should be ordering it soon), however I have a few questions regarding collimation.

I have summarised Astro Babys Guide to Collimation into the steps I need to take, and want you to check them over for me.

1) Adjust spider vanes if needed (Probably not)

2) Use a collimation cap to see if secondary mirror is centred with focuser. If NOT, adjust the centre screw on the secondary mirror.

3) Make sure the secondary mirror is presented as a CIRCLE when looked at through the collimation cap. If NOT rotate the secondary mirror <---I'm unsure of how to do THIS

4) Centre the secondary mirror on the primary mirror. Look through a collimation cap/cheshire collimator and adjust secondary mirror tilt screws (the ones that need a allen wrench - Im unsure about this step)

5) Allign primary mirror. Use Cheshire Collimator and adjust primary mirror screws until the crosshairs are pinpointed on the primary mirror centre spot.

Cheers!

Can you please read through it and make any corrections!

[Bizibilder]

Looks about right! The bits you are unsure about are quite simple. - to rotate the secondary you have to undo (slightly) all three secondary collimation screws (the little allen screws at the back of the secondary) you can then rotate the secondary (it will be VERY loose!) and then nip up the allen screws again. It is these same three screws that you use to adjust the secondary mirror tilt in part 4 above.

I see you have a Dob - good! - for your first collimation lie the tube horizontally (put it on a pillow or cushon!) so you don't drop bits down the tube onto the mrror!

Take your time as you first collimation may well take a while - after that it's like riding a bike - once learned you never forget.

[x6gas]

It's easier with a 'scope in front of you...

The bit I'm not sure about if what to do if yours is one of the 'scopes that Astro Baby says shouldn't have everything lined up centrally but off to one side. How you know how much to one side is well beyond me!