My 11 yr old nephew was given a National Geographic Dobsonian (I suspect one of the cheapies from Aust Geo or Aldi, not sure of the model number as I forgot to check. He and his parents were complaining it did not work, so it has beeen left outside, partly undercover. When I looked at it, I discovered the focussing rack was jammed, so I freed it up and I was the best uncle ever, for it now worked! However, having been left oustide without a front cap the mirror has some dust and dirt on it. I assume it will be front surface silvered, so what is the best way to clean it? I do have special professional grade camera lens cleaning cloths. Is it possible to remove the mirror? There are some screws at the back which I assume will alow me to remove the mirror. If I remove the mirror, is it just a matter of popping it back in? Or will it need to be aligned? If so, how do I do that?
Good onya Steve , on the cleaning just hit the " search" icon in the blue bar at the top of any IIS page and type in "cleaning telescope mirrors" you will find lots of good info on this .
Yes these mirrors have a basic hard coating ( MgFl ) and if careful it will come up like new , also check the small secondary mirror below the eyepiece focuser .
Good luck and please keep us up to date with your progress .
Photos would be nice .
Location: '34 South' Young Hilltops LGA, Australia
Posts: 1,493
Steve,
Do not rub any camera cleaning cloths professional or not on the surface. You will scratch the coating and possibly the mirror. Read up about it first.
The simple method I use is -
remove mirror from cell
submerge the mirror in a tub of tap water water,
soak to soften the dust,
use gentle running water to wash off as much as possible
Difficult to removing material? It probably won't affect performance.
If you must remove difficult to move material submerge the mirror and waft it off by gently dragging cotton wool over the surface without applying direct pressure to the surface.
Alternative : use a garden hose with the nozzle set to a fine high pressure spray. Be careful the nozzle doesn't come of an hit the mirror.
Rinse once or twice with generous quantity of distilled / de-ionised/ demineralised water. Some people like to use isopropyl alcohol for the final rinse to aid drying. I don't.
Place a towel next to the splash-back of a bench and lean the mirror against the splash-back almost upright so water can drain freely. The odd drying mark won't affect performance.
Good onya Steve , on the cleaning just hit the " search" icon in the blue bar at the top of any IIS page and type in "cleaning telescope mirrors" you will find lots of good info on this .
