Unable to collimate?

[Ed the Fox]

Hi all, I wonder if anyone could help.

Today I removed the focuser on my 130m and installed some ptfe to take up the slop. This worked just fine but needed recollimating as the secondary mirror did not line up any more.

I don't know who tightened the cross headed screw in the middle of the splines but it will not turn at all. It's stupidly tight.

Does anyone have any ideas at all to get this undone? Otherwise I cannot collimate the scope. 

Cheers in advance. 

[wulfrun]

Try slackening the three allen-headed screws a fraction, that should take the pressure off the centre screw.

[Ed the Fox]

1 hour ago, wulfrun said:

Try slackening the three allen-headed screws a fraction, that should take the pressure off the centre screw.

Cheers wilf I'll give that a go.

[Spile]

Go through the initial checks on here noting the position of the focuser https://astro.catshill.com/collimation-guide/ 

[doublevodka]

On 07/03/2022 at 15:26, wulfrun said:

Try slackening the three allen-headed screws a fraction, that should take the pressure off the centre screw.

Defo try this first, had the same problem with my secondary

[Ed the Fox]

Firstly thanks to @wulfrun for suggesting I loosen one of the Alan key sockets first. Worked a treat.

So having faffed around for a couple of days I tried out my collimation skills only to be disappointed in my attempts. Stars where blurry and not at all crisp as before. Collimation is not easy !

Now having tried again I realised the secondary mirror was not in the middle of the FOV so having re adjusted that I realigned the primary with tge following results.

Please let me know if its satisfactory or not. Many thanks all.

[Spile]

If you look at the diagram on my site you will see that a<b (confirmed by the dark secondary reflection “pointing” away rather than from the primary) and whilst not as bad c does not equal d. Sort out the offset error first so that a=b and then tweak the rotation/tilt error so that c=d.