Collimating question

rossh · #1 23-01-2008, 10:06 PM

Hi,
I have a 250 mm reflector on a Dobs mount. It's been in the cupboard for a while and have decided to check the collimation. I have used a home made sight tube and seem to have it close - except: when I focus the eyepiece inwards towards focus I get the concentric rings around a star. These get closer and closer together then at the point of focus I get a flare. I have been using Rigel as a target star and have found that at 250 x mag. the flare makes it hard to see the small Rigel B star. Also on the other side of focus, I don't get the concentric circles appearing again - this is what makes me think that something is out of alignment.

Any ideas, thanks

Ross

duncan · #2 23-01-2008, 10:16 PM

I dont know much but it sounds like your primary is out, (tilted) in relation to secondary.
Others on here will give you better advice.
Cheers