Expert: Paul Wagner - 2/23/2011

Question
Hello,

I would like to disassemble a primary mirror on a Newtonian telescope.  I can see that the mirror needs to be cleaned and I can't reach it.  I would also like to see how the collimation screws work so I can have a better idea of how to collimate it.  There are six collimation screws, three black and three white.  It looks like on the  inside of the telescope there are three points that coincide with the black collimation screws where the primary mirror is held on with two phillips head screws at each of the three points.

Do you know if I can disassemble this without harming the primary mirror?  I've never tried to take it apart before.  Any recommendations for cleaning a mirror (will glass cleaner hurt it?)?

Thank you!

Answer
HI Josh

Step one:  Be very careful.  A dirty mirror is still a lot better than a scratched one!

Step two:  the mirror mount itself is attached to the tube by those philips screws. Very carefully take those screws out, and you can slide the whole mirror mount ( including the mirror ) our of the tube.  The tricky part is the last couple of screws...because the rest of the assembly will be a little loose and sloppy at that point. And beware--the mirror weighs more than you expect.  When you take it out of the scope, the tube will be very unbalanced...and unless you restrain it, it will want to swing around.  Don't let it do that!

Step three: once you get the mirror mount out of the scope, you'll be able to see that it has some clips that hold the mirror onto the mount.  Put the whole thing on a stable table and take off or loosen those clips.

Step four:  Now you can take the mirror out.  

Step five: put the mirror in a bowl of distilled water and let it soak for an hour or so.  That will loosen up a lot of the dirt.  Then take a very soft cotton ball (not a Q-tip--as they will scratch the mirror) and gently clean the mirror while it is still in the water.  If it is still dirty, you can try adding a few drops of dishwashing liquid.  Rinse with distilled water, and let it drip dry.  At the very end, you may want to dap the last few drops up with another cotton ball, but if your water is really clean you won't have to.

Step Six;  Put it all back together again.

Step seven:  learn how to collimate your scope---because it's going to need it now!

Hope that helps

Paul Wagner