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Observatory telescope (non-electrical) dew solutions

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#1 Trackerthedog

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Posted 21 October 2020 - 02:01 PM

I know this might have been addressed in other questions, but I'd like to know if anyone with an observatory has found good (Non-Electrical) ways to prevent moisture / dew formation on their telescope when it is left year-round in the observatory. ... My observatory is built on rural land owned by a couple and I have to use their electrical power sparingly. ... I can't really leave a heater or dew heater band turned on all through the winter (also partly because of fire / insurance concerns). I live on Vancouver Island (just above Washington State) and it can get down to around zero or even minus 5 degrees F. here. .... I own a very large refractor and am mainly concerned about the back side of the objective lens - since I can place desiccant close to the external side of the objective. Placing little desiccant packs in the cap for the eyepiece end of the telescope doesn't really help (they turn pink in one or two days) since the OTA is 2200 mm long. ... My observatory is about 3/4 of a mile from the sea and is at about 300 feet of elevation - if that is helpful information. ... Anyway, has anyone managed to use purely non-electrical techniques / systems to protect the lenses of a large refractor that stays in their observatory year-round? ... Once again, I'm sorry if this question is repetitive or in the wrong forum, but I think it might be a kind of unique question. ... Thank you for any responses!



#2 Cliff C

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Posted 21 October 2020 - 02:23 PM

There was a product called "Damp Rid" that I used in my boat cabin back in the day. It did a fine job keeping mildew away. Two or three placed in my cabin kept mold and mildew away for the long winter. You will need perhaps a half dozen or so. Look into whether or not any byproduct gas is released that could eventually eat away at the lens coatings. 

Another idea would be to hook up a photovoltaic solar collector outside the observatory to power one or two dew heaters set to a low power setting. A little bit of heat should keep the lens elements dry.



#3 wrnchhead

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Posted 21 October 2020 - 03:26 PM

I have seen Vancouver Island from the south! I have to feel skeptical that there would be enough sunlight, especially as low as it gets up there (Plus clouds) in the winter to reliably power anything really.

I wonder if there would be some way to seal it such as vacuum sealed. In a plastic bag maybe with a desiccant in there? That shouldn’t get saturated very quickly assuming the seal stays good Interesting challenge.

#4 Trackerthedog

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Posted 21 October 2020 - 03:43 PM

I have seen Vancouver Island from the south! I have to feel skeptical that there would be enough sunlight, especially as low as it gets up there (Plus clouds) in the winter to reliably power anything really.

I wonder if there would be some way to seal it such as vacuum sealed. In a plastic bag maybe with a desiccant in there? That shouldn’t get saturated very quickly assuming the seal stays good Interesting challenge.

Thanks wrnchhead, I have managed to place a bag around the outer side of the objective with a desiccant (orange bead) in it, but I am most concerned about the inner side of the objective - since the eyepiece-end cap desiccant (little blue bags) seems to turn pink within a day or two. ... I am going to use some bucket desiccant in the observatory ... as well as charcoal briquettes - which I found are apparently very good moisture absorbers. I guess there is probably no way short of electrical to protect the inner side of the objective lens. Cheers.


Edited by Trackerthedog, 21 October 2020 - 03:44 PM.


#5 dhkaiser

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Posted 21 October 2020 - 03:50 PM

Desiccant inserted in the eyepiece end?



#6 Trackerthedog

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Posted 21 October 2020 - 04:01 PM

Desiccant inserted in the eyepiece end?

The problem with the eyepiece end desiccant is that the OTA is so big - 2200mm long - and the little desiccant bags get used up within a day or two -> and don't really help the farthest parts of the tube (where the back of the objective lens is).


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#7 wrnchhead

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Posted 21 October 2020 - 04:30 PM

Yeah, that's what I was supposing, the bag doing the sealing and the desiccant wouldn't get saturated so quickly that way, since you're creating a mini-environment independent of the outside air. 

 

There's always the heat sticks they use for gun safes, (electric) or an incandescent bulb, though you would want to be able to check on it's operation in person conveniently and regularly. I don't suppose those would draw too much current. I am expecting someone has solved this problem and will give you some real pointers. 



#8 John Fitzgerald

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Posted 21 October 2020 - 05:02 PM

Use dew heaters or 130 volt light bulbs.   Pay the property owner for the excess power? Even if it was 25 watts, 24/7, it's not much cost, $1.80 per month at 10 cents per kWh. For 40 watts,  it would work out to $2.88 per month.  Cheap insurance.


Edited by John Fitzgerald, 21 October 2020 - 05:08 PM.

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#9 ssagerian

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Posted 21 October 2020 - 05:21 PM

Are you gettting dew formation with the scope while its stored in the observatory? How is the scope normally stored? Im assuming its in a closed space? a dome or ROR with the roof closed? Are you still getting dew formation in those situations? Or are we talking about when its operating?  Roof rolled back, mirror and tube pointed out the starry night?



#10 John Fitzgerald

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Posted 21 October 2020 - 05:39 PM

I have had an 8 foot dome for about 11 years.  I use a water resistant canvas cover over the refractor when not in use. The refractor is parked facing the pole, with the counterweights at the bottom. The cover comes down just below the counterweight shaft.  The cover is left open at the bottom. The focuser and diagonal are covered with another canvas bag, secured to the lower tube. Under the cover is a 40 watt light bulb attached to the pier at about the height of the bottom of the counterweight shaft.  It's in a reflector type fixture facing up.

 

The bulb is on a timer in warm months to only run at night.  During the cold months, it runs continuously when the refractor is not in use.  Using a 130 volt bulb, they last generally about 4 to 6 months each.

 

Using this setup, I have never had a moisture problem.   When the refractor is in use on dewy nights, I run a 10 watt dew heater band around the objective lens cell.

 

In your situation, I don't see any viable alternatives other than using house current.  Some desiccant chemicals are corrosive,  and at any rate won't last long at all in an unsealed building. 


Edited by John Fitzgerald, 21 October 2020 - 05:45 PM.

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#11 Trackerthedog

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Posted 21 October 2020 - 05:45 PM

Are you gettting dew formation with the scope while its stored in the observatory? How is the scope normally stored? Im assuming its in a closed space? a dome or ROR with the roof closed? Are you still getting dew formation in those situations? Or are we talking about when its operating?  Roof rolled back, mirror and tube pointed out the starry night?

Hi ssagerian. It is a PodMax dome observatory. I understand the risk of dew formation when the slot cover is open and the observatory is operating. I am trying to find a good way to protect the optics (triplet objective lens) when the observatory is not operating. ... The PodMax sits on a wooden deck which is covered with outdoor carpet / covering. The base of the walls is not sealed, but the deck is sloped in 4 directions to allow any excess rain water to drain away. ... The concern is that, with the colder, damper weather hitting Vancouver Island  now, the scope's optics may start to cool below the dew point.



#12 Trackerthedog

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Posted 21 October 2020 - 05:48 PM

I have had an 8 foot dome for about 11 years.  I use a water resistant canvas cover over the refractor when not in use. The refractor is parked facing the pole, with the counterweights at the bottom. The cover comes down just below the counterweight shaft.  The cover is left open at the bottom. The focuser and diagonal are covered with another canvas bag, secured to the lower tube. Under the cover is a 40 watt light bulb attached to the pier at about the height of the bottom of the counterweight shaft.  It's in a reflector type fixture facing up.

 

The bulb is on a timer in warm months to only run at night.  During the cold months, it runs continuously when the refractor is not in use.  Using a 130 volt bulb, they last generally about 4 to 6 months each.

 

Using this setup, I have never had a moisture problem.   When the refractor is in use on dewy nights, I run a 10 watt dew heater band around the objective lens cell.

 

In your situation, I don't see any viable alternatives other than using house current.  Some desiccant chemicals are corrosive,  and at any rate won't last long at all in an unsealed building. 

Thank you for that information, John. It is obviously based on a lot of experience.



#13 John Fitzgerald

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Posted 21 October 2020 - 06:24 PM

Thank you for that information, John. It is obviously based on a lot of experience.

Yes, it is.  I have found something that works well, and am glad to share it with you.   It is very humid here, so what works here should work for you.  No harm in you trying it out for a couple months, and adjusting the wattage as needed. 



#14 Trackerthedog

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Posted 23 October 2020 - 05:41 PM

I have had an 8 foot dome for about 11 years.  I use a water resistant canvas cover over the refractor when not in use. The refractor is parked facing the pole, with the counterweights at the bottom. The cover comes down just below the counterweight shaft.  The cover is left open at the bottom. The focuser and diagonal are covered with another canvas bag, secured to the lower tube. Under the cover is a 40 watt light bulb attached to the pier at about the height of the bottom of the counterweight shaft.  It's in a reflector type fixture facing up.

 

The bulb is on a timer in warm months to only run at night.  During the cold months, it runs continuously when the refractor is not in use.  Using a 130 volt bulb, they last generally about 4 to 6 months each.

 

Using this setup, I have never had a moisture problem.   When the refractor is in use on dewy nights, I run a 10 watt dew heater band around the objective lens cell.

 

In your situation, I don't see any viable alternatives other than using house current.  Some desiccant chemicals are corrosive,  and at any rate won't last long at all in an unsealed building. 

Hi John, just one more question. Do you use the newer 40 watt light bulbs - i.e. the ones that don't produce as much heat as they used to? ... It is hard to find the old bulbs here in Canada. If you use the old 40 watt bulbs, then I will need to look for one of the new, efficient ones that gives off as much heat. Thanks.



#15 John Fitzgerald

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Posted 23 October 2020 - 05:48 PM

Hi John, just one more question. Do you use the newer 40 watt light bulbs - i.e. the ones that don't produce as much heat as they used to? ... It is hard to find the old bulbs here in Canada. If you use the old 40 watt bulbs, then I will need to look for one of the new, efficient ones that gives off as much heat. Thanks.

I use old style 130 volt bulbs. Regular screw base.

Try to find 130 volt bulbs. Most electrical supply houses will carry them.  They last much longer.

The set of six below might last you about two years.  At 120 volts, they will  be about 36 watts, mostly heat, and not blindingly bright.

 

https://www.amazon.c...03493075&sr=8-8


Edited by John Fitzgerald, 23 October 2020 - 05:49 PM.


#16 MalVeauX

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Posted 27 October 2020 - 07:19 AM

Heya,

 

Depending on what you're willing to do, since this is remote in many senses, is to look into off-grid solutions. Just depends how spendy you want to get.

 

Solar - You've already looked into this I'm sure. But, even on an over-cast day, there's energy coming down from the sky that you could be using. You don't need massive reserves, just enough to keep something 1 or 2 degrees warmer than ambient. This can be in the form of a light bulb or anything you can find that generates heat (including just warming strips at low temps).

 

Water & Color - Use black colors and paint everything to absorb heat. You can put in big drums of water that are sealed and paint them black. This is a common trick for people with green houses and plants. The drums that are black and full of water will heat up from exposure and store heat for a long while and release it overnight when its cooler around it. You can get creative with implementation.

 

Geothermal - This takes a lot more install, but if you drop some pipes deep below the freezing soil line, you can benefit from the temperatures down there being warmer than ambient. You could put one pipe down next to the pier and just cover your scope with a sealed cover with the pipe sharing its volume with the covered volume, should be a degree or two warmer than ambient during the really cold times.

 

I'm in Florida, 99% humidity all night every night and very common in the morning and evening too. Everything dews over immediately. My observatory is not sealed. I used to use different moisture absorption devices that would be good for a few days then need recharging. I used to use fully sealed covers over the mount & scope in the observatory and put a light bulb inside, then a safe warmer inside. Worked well. Dry as a bone. But was annoying to fool with all day. Now, I just cover the equipment with a clear shower curtain inside the observatory and it stays open so it can ventilate with the rest of the observatory space. My observatory is painted all white to avoid absorbing heat all day (Florida). None of my gear is dewing over at all these days, no matter if my humidity is 99%. The gear is protected from wind, so its ambient minus wind chill. Ambient is cooler than inside, so nothing dews over. And having a loose tented cover works miracles for giving a buffer of air between ambient and the equipment. Enough gradient to prevent dew formation even in 99% humidity conditions. I do the same with my outdoor grill and smoker; tented covers, no dew, no water formation on the grill, so no rust. I just applied the same concept but bigger scale to my observatory. So bottom line, put a tented cover over your scope/mount inside your observatory. It may be just enough to not need anything else.

 

Very best,



#17 Stevegeo

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Posted 27 October 2020 - 08:27 AM

A simple solution if going with he bulb...go  for an OVEN 40..watt  bulb

 

That's about the only ones that have not gone LED.. I use one in my Observatory in fall and spring when the dew is a bother. 

My dome is 9ft dia and a 40 at the base of the scope at the  mount will keep the dew all night.

I run it on a.few.hours before observing. Warms the pier up. The scope base and mount. The radiation alone from just this keep the dew off with shutters open most of the night.  My bulb is under the mount below the rat trap with foil on top . It radiates the heat mostly down into the steel pier which is filled with concrete just shy of the  top.

 

My next pier will have roof warming strips in the concrete .. radiant floor style.. this is very effective as it keeps the inside temp just above the dew point.   

Stevegeo


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#18 SteveInNZ

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Posted 28 October 2020 - 02:43 PM

One approach you may want to consider is replacing the moist air by purging it with air from a scuba tank which is required to be very dry. Then the dewpoint drops to around -50F and your desiccant only has to cope with any external air that leaks in. Duct tape and trash bags to the rescue.

 

Steve.



#19 t-ara-fan

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Posted 03 November 2020 - 03:07 AM

  •  I have to use their electrical power sparingly. ...
  • I can't really leave a heater or dew heater band turned on all through the winter (also partly because of fire / insurance concerns).
  • the OTA is 2200 mm long. ...

If all your gear is UL/CSA approved why would the insurance company care?

 

That is a BIG telescope. Pics?  

 

Use dew heaters or 130 volt light bulbs.   Pay the property owner for the excess power? Even if it was 25 watts, 24/7, it's not much cost, $1.80 per month at 10 cents per kWh. For 40 watts,  it would work out to $2.88 per month.  Cheap insurance.

Exactly.  I would put a dew strap on the dew shield, and two on the OTA right by the objective. Run the dew straps at 1 amp to make my calculation easier. 1kWh  per day is a dime. Maybe two dimes with the racket they have charging for delivery, riders, service, administration, green tax, fighting Alberta, etc.

 

I will go out on a limb and suggest a massive refractor, mount, and shack cost you $50K.   Six bucks a month to keep the fungus off that lens sounds like a bargain. 

 

Dessicants are not going to do it.  And I hope we never see a post from you asking "is this fungus on my objective". 

 

 




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