collimation fault

[ultramol]

Hi I was wondering if anyone can point me in the right direction. I am collimating my 200p and as I rotate the secondry mirror it never acheives a circle. It almost gets there but as it gets close it starts elongating in the other direction, never reaching a circle. I have never had this problem before but recently I removed the focuser and was wondering if it could be that

Many thanks    Geoff

[wimvb]

Can you center the secondary in the eyepiece (using a collimation cap)?

If so, then after centering you adjust the secondary by means of its collimation screws.

Collimation requires several adjustments to be made together to succeed. It's difficult to pinpoint what the problem is without actually being there.

(Which is another way of saying that the above is just one suggestion.)

 

BTW, sorry for the loss of your bins

 

Good luck

[acey]

The secondary mirror is elliptical in shape, and when viewed at an angle of 45 degrees you see it as a circle. If you can't see it as a circle then for some reason you aren't getting it to 45 degrees. Secondary holders in most scopes are frankly crude - I'd try manipulating the secondary mount by hand to try and bring the mirror to a circular appearance, then gently secure any loose bolts. I doubt that the angle of the focuser  would matter, there should be enough play in the secondary. If you can't manipulate it sufficently then make sure the adjusting screws are loosened, you've maybe got one screwed in too far. Just one precaution to bear in mind - do all of this with the tube horizontal, in case the secondary mount should happen to detach completely. Unlikely, but you wouldn't want it falling on your primary.

And I hope that whoever stole your bins gets the karma they deserve.

[ultramol]

Thanks for that help. I have never had any trouble before. I first centrer the secondry using a webcam and collimating circles, then use the 3 screws to adjust the angle of the secondry but for some reason I just cannot get it to form a circle. It is quite a bit off, I have always got it spot on using this method but for some unknown reason I cant get it now. Back to the drawing board.....Thanks again....Geoff

[REG78]

Have you tried your centre screw beside your adjustment screws fiddle about with tht I had to do th same until my secondary became a circle and centred in my focuser thn everything became a lot easier collimated hope ths helps out