DavidTrap
19-10-2012, 09:02 PM
Hi,
I bought a second hand scope recently and have had problems with the mirror dewing up at the drop of a hat. The scope has fans to help cool the mirror and I wondered if these fans are cooling the mirror below the dew point.
The mirror was rather dusty and I have also pondered if the dust was acting as a nidus to facilitate the dew forming.
Today, I decided to clean the mirror. When rinsing the mirror, I noticed that rather than the water forming 2-3mm beads, there were thousand of microscopic beads across the surface. These evaporated quickly to leave a clean surface. However, I am now concerned there could be fine pits across the surface which could also be acting as a nidus for dew formation.
When I first saw the beads, I thought it might be an oily film on the mirror surface, but it did not change with repeated washing (soap and running water only, not rubbing)
Obviously, my first step will be to try the mirror outside and see if it dews up, but the dramatic warming of the weather over the last couple of weeks might invalidate that test.
Any suggestions?
DT
I bought a second hand scope recently and have had problems with the mirror dewing up at the drop of a hat. The scope has fans to help cool the mirror and I wondered if these fans are cooling the mirror below the dew point.
The mirror was rather dusty and I have also pondered if the dust was acting as a nidus to facilitate the dew forming.
Today, I decided to clean the mirror. When rinsing the mirror, I noticed that rather than the water forming 2-3mm beads, there were thousand of microscopic beads across the surface. These evaporated quickly to leave a clean surface. However, I am now concerned there could be fine pits across the surface which could also be acting as a nidus for dew formation.
When I first saw the beads, I thought it might be an oily film on the mirror surface, but it did not change with repeated washing (soap and running water only, not rubbing)
Obviously, my first step will be to try the mirror outside and see if it dews up, but the dramatic warming of the weather over the last couple of weeks might invalidate that test.
Any suggestions?
DT