Collimation with a closed tube - placing the washer

[mountainstorm]

I've never had a problem collimating my scope as it's an open tube, but I got to wondering ... how do people collimate a closed tube?  How do they get the washer down to the main mirror and accurately placed?

Is there some special tool they use?

[Peter Drew]

I think the short answer is that they don't. Mirrors in closed tubed telescopes are often fitted with central collimating washers by the manufacturers, owners with mirrors that don't have them usually add them by removing the mirror cell.

[John]

I think all the newtonians I've owned over the years have had the central "washer" / marking applied by the manufacturer. As Peter says, if it's not there you need to remove the primary mirror cell and add the the central marking using a method similar to the one that Gary Seronik demonstrates here:

http://www.garyseronik.com/?q=node/168

 

Edited February 26, 2016 by John