I built a Krueger & Berry style Dobsonian strut Mount telescope a few years ago around a 12.5″ full thickness mirror that I swapped for. The only problem was that even though the mirror sits in a box, said box has no bottom; hence, it’s no problem for all sorts of dust, pollen, and god bows what else to land on the mirror; obviously, the more Schmutz that gathers, harder it is to see stars, planets, galaxies and so on.
When I inspected the mirror last week before a little neighborhood star party at the home of another telescope maker who lives North of Baltimore, The mirror was so disgusting that I removed the mirror from its box and cell and washed it off carefully in a laundry tub that I first washed out. (Recipe: wash tub, wash hands, rinse both, put mirror under tap, rinse off as much as possible just with its flow, then fill tub part way with lukewarm water, add a fragrance-free detergent, swirl that around with fingers, then start running your clean, wet, slightly soapy water gently around the mirror. Use fingernails to pick off anything you feel. Respect. Turn mirror. Rinse. Repeat. Then rinse a bunch more. Remove mirror from water, put it on a soft clean towel that’s not hot fabric softener, on its edge; use a clean washcloth to pat dry if needed on the front.
It worked great.
Btw I’m willing to do this because I can recoat it whenever I want in our club’s alumunizer.
But taking it out & putting it back in is a PITA, and dangerous, to boot — good chances of dropping it coming out or going back in!
So I designed an inner mirror cover. It took a lot of iterations, using measurement, a geometry drawing program, numerous full sized models made from corrugated boxes we were going to recycle, and hot glue – just for the five or six cardboard prototypes. Then I used some thin lauan plywood and some reinforcements carved by band saw from thicker plywood, and some plastic sheet, pink duct tape, and colored thumbtacks.
Here are photos of the result;