Older Skywatcher Dobson Collimate question

[Newbie2019]

Hello,

I have an older Skywatcher Dobson. Can you please tell me what screws I need to turn to Collimate the mirrors for the primary and secondary mirrors. Pictures attached. 

Thanks.

[Avocette]

In (simple) answer to your question, the primary mirror locking screws are the grub screws which are reached with a small Allen key type wrench, the adjustment screws are the cross head screws. For the secondary mirror, the adjustment screws are also grub screws requiring an Allen key. The cross head bolt in the centre of the secondary mirror fitting, holds the mirror against the pressure from the adjustment grub screws, so will need careful adjustment at the same time.

However, are you sure that you need to make ANY adjustment at all? Although the scope is an earlier model, the primary adjustment screws look just like my Skyliner 200p did in 2012. Behind the adjustment screws are neoprene O rings which after years may have lost their elasticity having been effectively ‘crushed’ during factory collimation. Even when new these O rings permit very little adjustment but good manufacturing tolerances probably make this approach adequate for most scopes. If you do start making adjustments you may well need at least replace the O rings with fresh ones, or better, change the adjustment screws and locking grub screws to longer ones and use small springs in place of the O rings. Then you could also spend on Bob’s knobs (which I ended up doing) for easy tool free adjustment. But this will mean that you cannot stand your scope (temporarily) on the bottom end of the tube without risking affecting the collimation.

[alacant]

2 hours ago, Newbie2019 said:

what screws I need

Hi

Secondary: m4. Remove the hidden screws -if there are any- using an allen key and replace with m4 screws. Much easier to adjust like this.

HTH

 

[RolandKol]

I would suggest, do not touch Any Screws of the Secondary at the start.

Colimate the primary Only, the secondary usually comes in close to perfect position from the factory.

So once you colimate Primary, which is quite easy, run a de-focused start test on the bright star and if you will get a Close to symmetrical result, - do not bother about the secondary as it may lead to even more issues.

The adjustment screws of the Primary mirror are based at the bottom of the scope.

[JOC]

Follow this http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

Do not deviate in any way, carry out every instruction no matter how odd it seems and you should get success.  A Cheshire Collimator is a good thing to have.