Collimation troubles

[Bryan196]

Hello all. Today I was trying to collimate my skywatcher 250 dob and ran into a bit of bother. The main screw in the centre of the secondary mirror holder is too tight, I tired to loosen it with a screwdriver but it just won't budge. Any ideas on how to loosen it without the secondary falling off? Thanks in advance

[Naemeth]

Hello all. Today I was trying to collimate my skywatcher 250 dob and ran into a bit of bother. The main screw in the centre of the secondary mirror holder is too tight, I tired to loosen it with a screwdriver but it just won't budge. Any ideas on how to loosen it without the secondary falling off? Thanks in advance

First of all, are you sure that the secondary mirror has been incorrectly positioned, because it is far more likely that it merely needs tilting if it needs anything. If the secondary is in the wrong position in the tube, that's more likely to be the manufacturers mistake or that someone has had a mess around with it, it doesn't slide up or down the tube on it's own!

For the tilt screws, there should be three around the main screw which will probably be hexagonal, so you will need an Allen Key. I've found a Metric set a great help, and I use the second smallest (2) on my mini Dob, I think it may be the same as yours, but it would be good to check .

In addition, never adjust anything unless the Dob is horizontal, you don't want a screwdriver denting or smashing the primary.

[Moonshane]

what you have to remember is that the three tilt adjusters push and the central screw pulls the secondary holder so they all work together to hold it in place try loosening the three adjusters and this will make the central bolt loose. as mentioned be careful not to drop the secondary but there's usually plenty of thread on the central bolt so it should not be too scary. occasionally if not adjusted for a long time you may have the firmly hold the secondary assembly with one hand (to prevent rotation) which you unscrew things with the other. be careful not to touch the surface of the secondary.

[Bryan196]

Thanks for the advice guys, will have to go try it out now

[Mr Q]

Bryan - Before you attempt any adjustments, you should do a star test to see IF the collimation is off. If you have'nt, the link below will show you how and what to look for.

COLLIMATION