Collimation

[Spile]

This is what I do when it comes to the secondary…

Initial steps/checks…

1) SPIDER VANE: UP/DOWN/LEFT RIGHT - Spider vane screws(4) - Check with ruler/pair of compasses/circle of paper to ensure centre screw is equidistant from wall of OTA. 

2) TILT: OUTER BOLTS (3) - Move the secondary away from the primary by tightening each bolt until resistance is felt by each bolt.

The secondary is now positioned sufficiently central in respect of the primary.

The next adjustments will take into account any minor adjustment errors made above.

3) AXIAL: UP/DOWN OUTER BOLTS (3) - Loosen each bolt equally to move the secondary mirror toward the primary until it is cantered in the sight tube

4) ROTATION: CENTRE SCREW - Turn the secondary until the secondary mirror is facing you and is circular

5) TILT: OUTER BOLTS (3) - Make small adjustments to each bolt until the primary mirror (r) edge is concentric with the secondary edge.

 

Repeat procedure (3,4,5) as necessary.

 

Edited June 19, 2021 by Spile

[John]

Personally, over the years, I've found it helpful in maintaining collimation to understand that very small / tiny adjustments to the collimation screws make quite a large difference to the tilt of the optical mirrors and also not to tighten things down. The locking screws on my 12 inch dob are not used at all unless I'm taking the scope in the car.

 

 

[wookie1965]

19 hours ago, John said:

I have a large washer between the secondary bolts and the secondary holder to stop that happening. I have also added the milk carton washers to the arrangement:

https://www.cloudynights.com/topic/446178-secondary-mirror-milk-jug-washers/?p=5775875

 

 

I did that with my 200p a 1mm washer and ptfe washer made collimation a breeze.

[PeterStudz]

1 hour ago, John said:

Personally, over the years, I've found it helpful in maintaining collimation to understand that very small / tiny adjustments to the collimation screws make quite a large difference to the tilt of the optical mirrors and also not to tighten things down. The locking screws on my 12 inch dob are not used at all unless I'm taking the scope in the car.

 

 

I certainly agree with the first part.

I’m new to all of this and I’ve been restoring an old Skywatcher Skyliner 200p. The secondary was way off under the focuser. At first it was most frustrating as I’d get it aligned under the focuser (which required large adjustments), but when I then aligned the secondary to the primary, also requiring large adjustements, the secondary was then back to being out of alignment with the focuser.

In the end I found it necessary to do small adjustment steps - getting the secondary slightly aligned to the focuser, then getting the secondary slightly aligned to the primary, going back and working on focuser alignment - repeat - until it was all in the right place. 

And I must try the washer thing. That sound like a great idea!

[wookie1965]

20 hours ago, PeterStudz said:

I certainly agree with the first part.

I’m new to all of this and I’ve been restoring an old Skywatcher Skyliner 200p. The secondary was way off under the focuser. At first it was most frustrating as I’d get it aligned under the focuser (which required large adjustments), but when I then aligned the secondary to the primary, also requiring large adjustements, the secondary was then back to being out of alignment with the focuser.

In the end I found it necessary to do small adjustment steps - getting the secondary slightly aligned to the focuser, then getting the secondary slightly aligned to the primary, going back and working on focuser alignment - repeat - until it was all in the right place. 

And I must try the washer thing. That sound like a great idea!

 

[iapa]

Don’t know if it will be useful but I posted the trials and tribulations associated with collimating my 10” CF

 

 

Edited June 21, 2021 by iapa
Typo correction

[doughnuts729]

Think I got it it was the twisting of the secondary that was causing the waining crescent like shape to one side like everyone said. It may not look perfect but my phone camera isnt quite at a right angle to the collimation cap eyepiece. Thanks to all that helped.

Edited June 22, 2021 by doughnuts729

[Mr Spock]

That looks really good 👍

[Mr Spock]

I've done my 250mm today. It's new and was in reasonable shape straight from the factory, but not perfect.

The secondary isn't quite central to its mounting (poor workmanship), so I adjusted the vanes to compensate. It was also a smidgen too far towards the primary. Like you I had a crescent shape - not bad, but, needed fixing.
Once I'd done that the secondary was adjusted so my laser pointed to the middle of the primary. Then the primary adjusted (that's the easy bit).

The hardest part is securing the secondary. It's fairly cheaply engineered and would 'fidget' on tightening. A little patience and it was sorted. I shouldn't need to touch the secondary again.

Tools used:
Home made collimation cap
Laser collimator
Bit of cardboard for underneath the secondary as it doesn't stand out too well against black.