Condensation in an APO triplet?

[skogpingvin]

Hi all, Bill here

Took my new scope out yesterday to the ASV dark site for some time with Eta Carina (fighting the glow from the Moon as well). It's a Sharpstar 107PH APO triplet. Next morning I noticed a layer of condensation on the lens - it was pretty dewy, so that's OK, but looking closely at it, I'm not certain it was on the outside of the lens. Of course, it's hard to tell just by looking, and I sure as hell wasn't going to touch it my my grubby paws! I left it in the sun for a half hour and it cleared nicely.

My question is: with an air-gapped triplet, is the gap open to the atmosphere, or is it sealed (in which case it should probably be filled with something like nitrogen, right)? Is this going to be a problem, or is it just something that happens and I can get around with some warming tape or something?

Any thoughts or advice are welcome.

[Wavytone]

+1 leave in the sun.

When finished observing leave it open in the car or bring indoors, rather than leave it sealed up in a box damp.

[Kunama]

I doubt any would be sealed within the cell. To clear it, place ota with objective end down in a warm location with diagonal end open so any moisture can escape. A sunny spot inside the house is better so no little critters make their home in it.

I use a Starlight Instruments 2" Desiccant cap and replace the desiccant every couple of weeks.

[glend]

I always bring my APO inside the house after a night of imaging, i don't leave it in the observatory. At the dark site i put it in the car. I wipe external dew off of course and put a dessicant cap on the rear and another inside the front cap, it always stays clear. You should be running dew heaters on the scope around the objective at this time of year.

[Slawomir]

+1 for desiccant cap. I use Farpoint. Also using two dew heater straps on the OTA on both sides of the lens cell - don't want to risk spoiling the lens with any moisture.

[leon]

Leaving in the sun is just stupid, :screwy: yes you will get dew and condensation whilst using your scope, that is normal, when finished viewing or photographing just leave it where it is and maybe cover it with a towel or something similar.

Taking it inside from 10 degrees to 20 degrees inside will form lots of moisture. :)

Just leave it covered outside and let it cool normally, unless you have an Observatory than just leave it alone :)

Leon :thumbsup:

[Kunama]

That is not going to remove moisture if that moisture has somehow got in between the lens elements as the OP suspected. If the moisture is on the inner lens surfaces and is not removed it will give fungus a nice healthy place to grow.
If there is moisture inside the OTA, it needs to evaporate out and the best way is to leave the tube in position where the moist air can escape. The desiccant caps will absorb any remaining H20... :thumbsup:

[N1]

The clasiest way to "leave it in the sun" is to attach a Herschel wedge and do some white light solar observing. Fungus won't like that either. 2 birds, one stone. :thumbsup:

[The Mekon]

I would use a bit of Leon's and a bit of Matt's advice here. I agree it is not the best to take it straight inside the house. But putting it out in the sun the next day for a few hours will help dry out any residual moisture. Never put the scope in the box and shut the lid after a nights observing. If it has to go in the box for transport, leave the lid open or open as soon as you are able.
I used an AP 130EDT for 22 years many times in icy and wet conditions. Always put the scope in the garage in the open when done for the night. When I sold it the lens was like new.

[casstony]

For general storage don't put the scope in a case, unless it's an airtight case with dessicant. Otherwise just leave it covered with a towel to let air circulate and keep dust off. You can leave the objective cover off or put it on when the air in the room is especially dry (after heating has been running for a while for instance).

[Kunama]

+1 :thumbsup:

I leave mine in the car with the case open. I would leave it at the observing site but I fear Phil would just add it to his collection :mad2:

[kittenshark]

Desiccant in its carry box/case is a must. I've 3d-printed some desiccant caps for a customer once. Big fat one for an Esprit 80. I think it'll help.

[LewisM]

Desiccant gel packs (bought separately or retrieved from packing of other goods) - zap in the microwave for 20 secs or so to refresh.

I just tape the sachets inside my lens (camera) or dewshield covers and stoof one in the diagonal nosepiece. Viola, and no need to buy fancy schmantsy anodised caps - just remember to remove the one in front of the diagonal before use :)

If you don't like the idea, blame Brian - it was his idea hey bro! :P

[Exfso]

I don't put the dew cap back on instead I use a "beany" over the dew shield, allows airflow and keep unwanted out. Next day take the beany off and put cap back on. I found originally by putting the cap back on after viewing that there tended to be a layer of moisture form on front of lens. Now none at all, yeah also use dew strap as well.

[LewisM]

Agree Peter. If I am at home, I'll simply bring it in without the dewshield cap on, and put it on the mount. I'll then put one of those air conditioning / hospital blankets over it (the open-weave ones). Let it dry. Then cap it.

If I take it out to the Dark Side...errr...site, I'll wrap the scope in an aerobics neoprene floor mat, and leave the cap off - it has about 8" of neoprene hanging over the exposed end anyway. Protects it for the ride home (it rides in a bubble wrap lined box) and lets it breathe.

The dewheater straps just about mitigate it altogether usually anyway :)

[leon]

You know what Guys I had a Tak Imaging system, some of you may know of it and I did take some reasonably good images, :shrug:

Admittedly it was in a low cost observatory and some nights when i was finished it was dripping after a -2 frost.

I would never warm it, but left it open with a fan running constantly all night and day.

No issue with moisture,taking a cold scope/camera inside is looking for trouble leave it out side to come to room ambient temp and it will be fine

Do it the other way if it going to be a big freeze and you want to be out in take it out well before dark and let it cool, right.;)

Leaving in the Sun is just stupid, :sadeyes: I have seen this at Astro Camps where people leave their stuff in the red hot Sun all day :screwy:

Leon :thumbsup:

[skogpingvin]

OK, I'll leave it to dry in the morning, but not in the sun, and leave the box open on the way home with the cover off (maybe a cloth over the end to stop anything falling onto the objective). At home, it doesn't normally live in its box anyway, I leave it up on the mount with the cap on.

As to dew straps, I'll get enough for a 4" refractor - but I have more questions?

First, will the ones below (for a 4" tube) be the right ones - and will the controller I've linked to be the right one?

https://www.bintel.com.au/product/kendrick-premier-heaters/
https://www.bintel.com.au/product/kendrick-micro-d-controller/

Second - and possibly stupidly - where do I wrap the strap on the tube? The optics at the end of the tube are hidden under the dew hood (about where the second "s" is in the photo), so if I wrap the strap around where the optics are, won't they be nicely insulated by the small air gap between the hood and the tube? Alternatively, should I wrap it around the tube at the base of the hood when it's extended?

I hope these aren't dumb questions. :help::thanx:

Bill

[Slawomir]

Hi Bill,

Might be best to ask the guys at Bintel - they are very helpful. I use Digifire and two straps ,and so far it kept dew away for miles! :lol:

http://www.iceinspace.com.au/forum/attachment_browse.php?a=212596

[LewisM]

Yeah, but you fry your chruschiki on your scopes Suavi :)

I use one generic, Chinese made $35 a pop heater strips on mine - no dew problems yet, and there have been some sopping nights lately. Good thing about these is they have their own built in heat controllers, so you don't HAVE to use a standalone controller if you don't want to. One push is low (green LED), then 2 more pushes is hot (red LED). Good enough for me.

[Slawomir]

Chrusciki and pierogi! :lol:

[skogpingvin]

Goodness, is there a mount under all that spaghetti?

So two straps - the blue one on the bottom end of the hood and the black one on the upper end of the tube?

Thanks!

Bill

[skogpingvin]

Mine's a haluški, thanks. Married a Slovak.

[Slawomir]

That's right. On one night I had dew forming on the inside of the lens, that's why I have now two straps that gently heat up the areas in front and behind the lens, and use desiccant plug after each session.

I will one day tidy up the wires, (when I will build an obsy), but in spite of all the wires, it is actually very quick for setting up and packing up - it takes me only about 5 minutes to set up the telescope and perhaps 20 minutes to accurately polar align.

[skogpingvin]

Sounds like a good idea - I had what looked like condensation inside the air gap last time I went out. I didn't like that!

[Marke]

little tip dont buy an expensive desiccant plug just find an old plastic film canister and put a couple holes in the end and grab some little desiccant packs off ebay for a couple bucks and put them in it and cap it off , it does exactly the same job :)