Theoldboy Posted October 10, 2019 Share Posted October 10, 2019 Bresser 10 inch Dob, I have just noticed stains on the end of the scope, on the part which looks like an alloy plate, where you adjust collimation etc., is this normal, or does it need to be returned?. many thanks. Link to comment Share on other sites More sharing options...
Theoldboy Posted October 10, 2019 Author Share Posted October 10, 2019 Anyone?. Link to comment Share on other sites More sharing options...
Carbon Brush Posted October 10, 2019 Share Posted October 10, 2019 They look like water stains from your photo. Or maybe a bit of surplus glue from any mirror pads? If so, definitely unexpected. But not doing harm. It is the front of the mirror that matters. Some more pics would help. David. Link to comment Share on other sites More sharing options...
joe aguiar Posted October 10, 2019 Share Posted October 10, 2019 Agree with guy above wont affect anything. It could be from dew or since dobs r really close to the ground was there tall grass there that could have touch the bottom? Link to comment Share on other sites More sharing options...
Astro-Geek Posted October 13, 2019 Share Posted October 13, 2019 When you say alloy plate, if you mean the whitish coloured disc in the centre, that's the underside of the primary mirror. A ten inch primary mirror blank is solid glass almost two inches thick, so the dried water droplet marks are totally isolated from the crucial front silvered surface. I'd agree with the theory that they're where droplets have evaporated from condensation. You could safely wipe them gently with a dampened piece of kitchen towel if you wanted to make certain, but there's no need to do even that really. 1 Link to comment Share on other sites More sharing options...
Rob Sellent Posted October 14, 2019 Share Posted October 14, 2019 Those water stains are on the underside of your mirror, so in theory shouldn't affect your viewing. Other than that, my advice is to not touch your mirror. You're only going to be putting unnecessary wear and tear on the coatings and if you think about it, even after you've 'cleaned' the primary if you look at the mirror in the daylight it is still going to look dusty. Use a bulb blower to blow off any obvious debris, pollen etc after a night's session and leave it at that. In a good few years, if the primary starts to sprout its very own ecosystem, then it might be worth a tender wash, but only if it affects the contrast and quality of image 1 Link to comment Share on other sites More sharing options...
Astro-Geek Posted October 14, 2019 Share Posted October 14, 2019 (edited) Good emphasis there from Rob, I should have qualified my remark about casually wiping the underside of the mirror. That's fine, as the glass blank is very thick, but the top surface that is coated and shouldn't even be touched. This photo of a ten inch mirror removed from the tube but still in its metal holder shows just how thick the glass is compared to the diameter. Needless to say, removing the Primary mirror "cell" like this should only be done with extreme caution and under extreme circumstances. It's too easy to drop it or touch it with hands or tools, which could immediately damage the mirror coating which lays on the front surface of the glass, unlike household mirrors which are coated on the back surface. Edited October 14, 2019 by Astro-Geek 1 Link to comment Share on other sites More sharing options...
Theoldboy Posted October 18, 2019 Author Share Posted October 18, 2019 Thanks guys, for setting my mind at rest. Still not used yet, weather cloudy and wet. Link to comment Share on other sites More sharing options...
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