Dob collimation Help Please

leon · #1 16-07-2010, 03:56 PM

Hi guys I am no new one to Scopes, however I have never owned or used a Dob.

A friend of mine has rushed out an bought a 10'' Dob and because he and me have no idea of how to collimate it,

could some kind person assist.

Now if it were a Tak imaging set-up no worries, but a Dob, no idea.

Leon

erick (Eric) · #2 16-07-2010, 04:04 PM

Do you want me to try and pop up to Ballarat over the weekend with tools in hand, Leon?

What is the make of the 10", please?

Ian Robinson · #3 16-07-2010, 04:57 PM

http://www.skyandtelescope.com/howto/diy/3306876.html

A cheshire and laser collimator and will be a big help too.

http://www.catseyecollimation.com/

mental4astro (Alexander) · #4 16-07-2010, 10:30 PM

Hi Leon,

What Ian is alluding to is the system I use, both the Cheshire EP and a Laser collimator.

The Cheshire optimises the position of the secondary mirror, which the laser doesn't. The laser optimises the alignment of the mirrors, which the Cheshire might be a little soft on, and tricky to achieve without two pairs of hands.

I tried the Cheshire on its own- hard work, and best left to deal with the position of the secondary relatively to the focuser. Tried the laser on its own- no good as it can get the beam reflected back on itself without the secondary's position being optimal. Together they compliment each other brilliantly to get the most out of your Newtonian.

Ian Robinson · #5 17-07-2010, 06:36 PM

Yes. That's what I do.

I have also discovered that when using a 5mW red lasercollimator that if you look at the back of the mirror in dark conditions that I can see a red spot of light (quite noticeable) and so rather than sticking a Catseye centre marker on the front (I bought some before I noticed this) I simply marked the back of my mirror with a small carefully centred circle in indelible marker.
Aluminium have about 90% light.

I have also been thinking of putting a very small dot in the centre of my diagonal on the front surface too but not sure if this will show up in imaging.
Comments anyone on marking the secondary to assist centring. ???

My Chesire is a 1.25" version and I can't see all my diagonal in it. I'll buy a 2" version one day.

leon · #6 17-07-2010, 08:44 PM

Many thanks guys, I have talked to the new owner of this scope and now it has been sorted.

What would i do without, IIS.

Leon

Ian Robinson · #7 17-07-2010, 09:09 PM

Quote:

Originally Posted by leon

Many thanks guys, I have talked to the new owner of this scope and now it has been sorted.

What would i do without, IIS.

Leon

Google or join a club (can always find a newtonian / ATM guru there).