Secondary Collimation Confusion

[Crimson Sunset]

Hi all,

A bit frustrated here, I'm trying to get my secondary aligned under the focuser but so far i can't get in aligned in the vertical axis. I can centre it with equal gaps left and right and can get it nice and circular, but the gaps at the top and bottom are completely uneven, theres seemingly no way to adjust this axis I'm using a cheshire/sight tube combo so the view is fairly tight.

It was centred fine before but has lost alignment somewhere along the line. Do i need to square the focuser or am i missing something obvious?

[Merlin66]

Maybe you've moved the secondary mirror downwards while trying to get collimation.

The secondary should look circular in the cheshire.

Shouldn't be the focuser alignment if it was OK before....

[Parus major]

That axis is adjusted via the bit knobs holding the spider veins. Us a metal ruler to get them all level and then tweek by eye.

[acey]

If "vertical" means the long axis of the scope then you move the secondary along that axis by loosening or tightening the screw in the centre of the secondary holder (hold the secondary while doing this in case it drops off!).

If you mean the axis perpendicular to this (as seen through the focuser), first try twisting the secondary by hand. If that doesn't work then check that the secondary holder is centred (using a tape measure). If it's not then adjust the secondary vanes. If it is, then the problem must be the focuser - but if it's only a small amount off-centre then you're not going to notice it at the eyepiece. Do a star-test with the star exactly in the centre of field: if the rings look circular with the dark spot centred in the rings then you've got nothing to worry about.

[Crimson Sunset]

Thanks for the advice

As it turns out, i am an idiot and didnt realise i'd put the secondary at a stupid angle when adjusting the tilt when i collimated it the day the scope arrived, sending the mirror off at a daft angle. After i got the tilt back to a normal angle it was fine, just goes to show how much experience plays a part in this process.

Thanks again everyone, glad i got that sorted out and regretting having to ask in the first place

Cameron.