Cross over hairs on collimating eye piece

[Jim Gillard]

Hi All, probably been asked loads of times before but hear goes anyway have just got myself a Celestron Cheshire Collimating eyepiece put into my Tal 100RS could just make out the spots merging into one enogher so great no problem there but the merging spots are out of alighnment with the cross hairs and not at centre point of cross over hairs mind you if the circles had been at that point of cross over hairs I would not have been able to see them anyway surely the awnser would be to remove the cross over haires a bit like a filter but of course I can`t do that.

Will I still need to correct the converging spots to bring them into the centre of cross over hairs and is this also to do with the ajustment of cullimating screws.

[umadog]

Yes, you need to center the spots under the cross hairs. John Reed Home Page Collimation - Cheshire

[Jim Gillard]

Cheer`s umadog I assum the reason the rings are off central axis is to do with the focuser alignment and only the more expensive refractors supply ajustment for this.

[umadog]

Ooh. Sorry! You have a refractor? It seems logical that you would need to measure and correct at least two things to achieve axial alignment but I don't know which two those would be. I'll therefore shut up and stop guessing

[AndyH]

Before fiddling with the Tal's lens cell, have you done a high power star test? Preferably 'straight through', without the diagonal? How does the image look in and out of focus?

Bare in mind the supplied Tal diagonal is collimatable and sometimes can be a bit off and needs a bit of a tweek. Simply take the backplate off to reach the sprung screws.

Andy.

[John]

One way to find out if the focuser is square is to use a laser collimator (accurately collimated itself of course !). The red spot, as the laser beam exits the scope at the objective end, should be in the centre of the objective lens.

The star test that Andy mentions is worth doing as well.

The cheshire that I use for collimating refractors does not have any cross hairs.

[Jim Gillard]

Thank you every one for all your comments they are very helful and I have learnt a lot.