Keyboard Shortcuts
Likes
Search
Moisture on primary mirror - frosty morning
¿ªÔÆÌåÓýThis morning there was heavy frost here in New Mexico, 22 degrees
F, and while observing Jupiter at dawn I had to use a hair drier
frequently ( on low setting, gently ). When I ended my session and
was replacing the front cover lid I noticed that there was
moisture on the primary mirror inside the scope.? I never noticed
any moisture before on the primary mirror all through last year
and I used the scope a lot. I keep the telescope always in place outside under a telegizmos cover. It is never inside. Is this common to have moisture develop on the primary mirror??
See moisture at arrows in pic. I wonder if something changed ( unsealed or something? ) over the course of the year with my C14 Edge HD? Thanks in advance for any replies. Thomas
|
Gary Jarrette
¿ªÔÆÌåÓýHey Thomas ? I have never had this problem because I have a permanent observatory but you might have luck with putting a low wattage light bulb, filament type, under the cover to keep a gentle heat under there. I do not know if anyone else has or does this but it would be interesting to see if someone has. You only need to elevate the temp perhaps 10 degrees above ambient to keep dew from forming I would think. It goes without saying that you should have a dew shield and a dew heater but as far as storage goes the bulb may be enough. ? The bad part of getting moisture on correctors and mirrors is that there is usually already a fine coating of dust on these elements and when the dew appears it turns this dust to mud which then sticks to the lens or mirror and makes it harder to clean without removing the mirror and putting it under running water after soaking in a mild soap solution. ? ? ? There are many good articles and YouTube Videos on cleaning but preventing this in the first place is better of course. An ounce of prevention is better than a pound of cure! ? That small amount of heat might be just enough to prevent condensation. It usually gets very humid just before dawn as evidenced by the dew on the lawns. ? It is a very common thing to put a cloth over a frost sensitive plant with a light bulb under it so this might work for the scope. It is just a miniature heater of course. Maybe 60 watts could help. ? You would of course have to make sure the bulb is in a cage or something to prevent a fire hazard. That is what I would do if my scope was outside. ? I wonder if anyone else has tried this bulb heating idea? ? Gary ? Carpe Noctem. ? From: C14_EdgeHD@... [mailto:C14_EdgeHD@...]
Sent: Friday, November 6, 2015 8:29 AM To: C14_EdgeHD@... Subject: [C14_EdgeHD] Moisture on primary mirror - frosty morning ? ? This morning there was heavy frost here in New Mexico, 22 degrees F, and while observing Jupiter at dawn I had to use a hair drier frequently ( on low setting, gently ). When I ended my session and was replacing the front cover lid I noticed that there was moisture on the primary mirror inside the scope.? I never noticed any moisture before on the primary mirror all through last year and I used the scope a lot. I keep the telescope always in place outside under a telegizmos cover. It is never inside. Is this common to have moisture develop on the primary mirror?? See moisture at arrows in pic. I wonder if something changed ( unsealed or something? ) over the course of the year with my C14 Edge HD? Thanks in advance for any replies. Thomas ? ? |
"Are you inserting the camera into an external focuser or directly into the rear of the SCT?" Direct.? Don't use an external focuser or anything else (e.g. no filter wheel). It is a pre-HD OTA with no vents. So once it is closed it is pretty much sealed.? Also, I use a front-end cooler (replaces the secondary)?prior to nightfall, so the inside?is?fully exposed to?twilight?humidity.? Maybe I should incorporate a desiccant into the cooler fan. Stan |
Also on my corrector I get no moisture on either the inside or outside because the corrector heated a very?small amount above ambient which insures no dew will form. The? DIY circuit I posted earlier measures ambient temperature and the temperature of the corrector then automatically keeps the optics above ambient.
|
"The? DIY circuit I posted earlier measures ambient temperature and the temperature of the corrector then automatically keeps the optics above ambient." "You could market that device, though it would not make you rich. <g>" I know. In 1999 when I first posted the DIY circuit? for ATMers??there were no commercial? dew prevention circuits? on the market that monitored ambient temperature?and optics temperature and automatically kept the optics above ambient. |