Whats the best way to get moisture out of a SCT?

[g__day (Matthew)]

I guess their was either a leak or a bit of condensation - but when I balanced my scopes the other day I noticed about 50ml of (hopefully rainwater or condensation) inside my main SCT.

I tilted it on the mount so the lens pointed down and most of it eventually dribbled out thru the seam at the front of the OTA. I notice the mirror still has condensation on 50% of it and so does the main corrector plate - on the inside.

What is the best way to get rid of the remain water - just wait for a sunny day and take the rear eye piece off and let the sun slowly evapourate it? Blow it carefully with a hair dryer on the rear and front of the OTA?

Secondly - how to prevent this happen again?

Thirdly does it need a service (or how do you decide this) when this sort of thing happens?

[casstony]

Since you live in Sydney give Bintel a call and get a price for service. Alternatively it's not hard to remove the corrector, cover everything with a fine cloth and wait for it to dry out. You need to check for orientation marks and shims and make sure it all goes back the same way.

[g__day (Matthew)]

Tony,

Thanks I know the guys at Bintel well and am well aware they service equipment. But my questions remain unanswered so to re-state:

1. What is the best way to get rid of the remain water - just wait for a sunny day and take the rear eye piece off and let the sun slowly evapourate it? Blow it carefully with a hair dryer on the rear and front of the OTA (or blow warm air in from the rear eye-piece?

2. Prevention - is this common - is the cause likely condensation over time or a leak in a roof in the wrong spot?

3. How do you decide if it needs a service or not (versus whom to do it)?

Matthew

[acropolite (Phil)]

I'm with Tony, I'd take the corrector off pronto and let the thing dry out thoroughly. Removing the corrector plate is easy, I had to do it to retighten a loose secondary holder, the plate should have alignment marks, if not put a small mark at the outside of the plate and on the tube to indicate alignment. It won't be necessary to remove the secondary from the plate but if you do make sure that is marked for alignment as well. Whatever you do don't leave the water in there, it takes no time at all for mould to form and the any form of mould usually will result in permanent damage. I'd be trying to work out where the water has come from, I've never had any moisture at all inside my SCT OTA. Here's a page on corrector removal from Jan's LX site

[OneOfOne (Trevor)]

Leaving it outside on a warm day should evaporate the remaining water into the air in the tube, but you would still need to exchange the moist air for dry air from outside. The baffle tube means you can't leave it face up or down and expect the air to find its own way out... Leaving it on it's side would be the best compromise, but of course the baffle will still prevent the air from easily getting out. The best option would be to take the corrector off...better you than me!

If you don't want to take the corrector off, or if it was me, I would put it outside on a warm day to let the whole thing warm up and evaporate the remaining water and put the Cat Cooler into it and leave it run for a couple of hours. The cooler would change the air in the tube easily, but I am guessing you don't have one. Otherwise you need some way of sucking the existing water laden air out of the tube. I have only had mine for 5 months so I can't say if it is "normal"...I suspect it is not.

Good luck!

[Mark]

I agree with Phil. Pull the corrector and let it dry out thoroughly. Do not use a hair dryer to blow warm air in the rear port. Do not use a hair dryer to blow inside the tube once you pull the corrector.
I used a sunny day to dry out a C5 some years ago, but it only had a 50cent size area of condensation on the inside of the corrector. Worked well.

I then used a silica gel pack snugged inside the rear port to keep the moisture out. I never had a repeat of the condensation, but I don't know whether it was the silica gel or good management.

An SCT is not really a sealed tube, so if water drips or runs onto it, it WILL get in. You should definitely check for leaks. If it's just a case of condensation over time, the silica gel packs will stop that. Alternatively, you may consider a dehumidifier of some sort if it's a fixed observatory.

Hope this helps.

Mark

[sheeny (Al)]

50mls! You know how to make an SCT owner uncomfortable! I just had to check mine - nothing luckily, but the reason it worried me is that I have experienced strange "fogging" phenomena on some nights when imaging the moon. The ToUcam just loses all contrast like the objective was fogged over, but it is clear as is the primary mirror... I haven't solved that one yet...

Sounds like those more experienced are suggesting the corrector plate needs to be removed. I don't have the experience but that sounds like good advice to me as long as you're confident about doing it.

If you really want to try to remove the moisture without dismantling you'll need a way of heating, drying and circulating the air in the OTA. If you have an SCT cooler, and air conditioned room you might get away with it. Crank the air conditioning up to warm/hot and circulate the air through the tube with the SCT cooler. When it's all evaporated, continue to run the cooler and bring the room temp down, so eventually you end up with a cool, dry tube.

You could try leaving the OTA out in the sun to warm and evaporate the moisture, but the rate of diffusion through the rear hole will be excruciatingly slow.

Keep us posted. I'm fascinated to know how it got there. I trust you haven't used it as life preserver!

Al.

[wasyoungonce (Brendan)]

Silica gel is a good idea but it absorbs only so much moisture and can do no more (ie: it changes colour from blue to pink...sometimes the beads turn white).

You can re-activate the gel sachet buy putting it in the oven on a low temp to draw the moisture out or the beads. But, you cannot do this if the sachet is in the OTA.

Better to have a sachet in the SCT visual back assembly, maybe put the sachet in a holder like an old plastic film cannister that has holes in it that lead into the OTA.

[rumples riot]

Yep, remove the corrector plate. Very easy to do and will be the best way to remove the moisture.

Of more concern is you getting moisture of that amount in the first place. I have had that quantity of water in my SCT's in the past.

To remove the water, try to use a lint free tea towl. That will get most of it out and then let it dry naturally. If you look in my sig there is instructions on how to pull an SCT apart under peltier cooling a C14. They are all basically the same construction.

[matt]

Originally Posted by sheeny

50mls! I'm fascinated to know how it got there.

Me too, Al.

That seems like a lot of water, just from condensation

[beren]

Noticed in your gear pics the inside of your observatory is covered with black ground plastic sheets, would that be contributing to high humidity levels ? for future prevention might be time to invest in one or two these http://www.pwtec.com/ddcap.htm

[g__day (Matthew)]

Well both ends are always capped - but yes plastic would keep moisture in apart from the roof of the dome where there is 1/2" gap to breathe!

What a night that was - came home early and finally got all moisture out of the OTA... Then the main PC wouldn't boot past Windows screen - lovely - after 5 Windows restores it finally booted.

Then it wouldn't connect to the hand controller - so restarted that. Tracking wasn't as good as before so I only slightly adjusted counterweights. Scopes where still aligned well even though I'd tightened retaining bolts on the 5" MAK. Focus was slightly out on my main OTA - took about 5 steps forward and 12 steps back on the Meade electronic focuser to get focus to where it was. Then the lever of the DEC friction clamp simply broke in two under minimum pressure! Used a 13mm spanner to work it last night. Centred on a star and all gotos were excellent - so pointing is still brilliant. Then I trained PEC again and 10 minute guided shots looked fine.

So I would say I can balance the counterweights better - then see if I am better than 1 arc second a minute off RA drift.

Took hours to get it all back to where it was (apart from adjusting position of the counter weights). One more cloudless night will see how well I can tune it before I start seriously playing with MaximDL for guiding and PEMPro for PEC training and / or polar alignment check!

Rang Bintel and I think I will take it for a service and clean next year once its all quiet. The front corrector looks like it has a small smear on the inside and I think a tiny white bug has invaded!

Great fun these challenges!

[GLENN A DAVIS]

Make sure that before you remove the corrector, to mark the orientation position of it relative to the tube.
A small texta mark on the edge of the corrector and one on the metal section where the corrector fits, will asure it goes back in the same position!

[g__day (Matthew)]

I ponder did it rain once recently and I somehow didn't notice? Its goy a super sized lens cap - maybe it acted like a rain scoop - and I didn't notice water was in it and it slowly leaked into the OTA?

I'm kinda at a loss to really know what has happened.

Anyway - my mission is not to get tracking as good as I can - so to polar align it as best I can - then seeing if I can really hone the tracking.

Once tracking is top notch - I'll look to get the OTA cleaned and serviced, then start dreaming of an S-BIG!

[astro_nutt]

Just a thought..every seen those damp-absorbing kits for areas prone to high levels of moisture..might be a worthwhile investment!!
Cheers!