Internal SCT Dewing

[Earl]

My 9.25 is suffering from really bad internal dewing Mirror and inside the corrector, any advice how to deal with this?

[Psychobilly]

Gave you got any bags of dessicant....?

I drilled a couple of holes in the bottom of an old 35mm film pot put a dessicant bag inside it and then would leave this inside the Visual back... make sure it can't fall through uding tape to form a lip...

For the initial dry out put the OTA and a couple of dessicant bags in a sealed plastic bag...

You can but Dessicant Eyecap plugs...

http://www.optcorp.com/product.aspx?pid=12725

Peter...

[Doley68]

Earl is spot on.

I recently had dew on all surfaces of my refractor, front, in the air space and on the innermost surface.

I thought that I may have to take the lens cell apart.

Then I remembered that I have a ready supply of silica gell pouches at work & thought I'd try it. One taped to the back of the objective lens cap & one resting just infront of the diagonal in the draw tube & Hey Presto, totally clear the next morning!

I just need remember to take the one out of the drawtube before observing:)

They can be recharged by baking in an oven for two hours at 120 degrees C.

[Earl]

I have ordered some so ill report how it goes.

[Lars]

I also use silica gel in my 9.25 but mainly when I am about to store the scope for some time since I find the gel rather slow working.

To get rid of the dew I point the scope a little downwards, put on the dew heater I have around the corrector and remove the diagonal or camera from the back so the moist can be vented out of the scope. This works fine for me and i get rid of the moist in a couple of hours.

/Lars

[Earl]

I have some silica now, but i have to report that i now have mold growing on the internal flocking !!!

This says things are way to damp in there!

[E621Keith]

I keep my C925 in a plastic box with bathroom sealant applied to the lid. I put the mount on top of the lid to keep it air tight. cheap alternative to peli case.

SAMLA Box - transparent, 79x57x42 cm/130 l - IKEA

Then I put something like this in the box with the c925

Moisture Absorber Unit from Homebase.co.uk

You can get one from Tesco or as ASDA for a quid, but I can't find a link for it.

I use these reusable silica gel pack for my eyepiece case and the peli 1500 case where I kept my APO. They turn pink when they are full. The silica gel pack needs to be recharged every month for the APO, so one pack is no where near enough to handle a c9.25, which is why I went for the larger pot for the c925.

2X Silica Gel Desiccant Moisture 4 Absorb Box Reusable | eBay

[michael.h.f.wilkinson]

Beware of that mold! If it gets into the coating you have a serious problem! I always put every back of silica-gel I find in any package into the box containing my scope, and it is stored in a very dry place.

[LukeSkywatcher]

My SCT has thus far been stored in the back tv room. The heating rarely goes on in there. I think i'll have to move it to the lounge so it doesnt dew up or mould grows on it. The room has had damp problems in the past.

Just means longer cool down time when i take it for a walk.

[michael.h.f.wilkinson]

My SCT has thus far been stored in the back tv room. The heating rarely goes on in there. I think i'll have to move it to the lounge so it doesnt dew up or mould grows on it. The room has had damp problems in the past.

Just means longer cool down time when i take it for a walk.

My Garage in largely unheated, so it could get damp, but putting a healthy amount of silica-gel in the box of the scope does the trick. I also allow it to dry in a warm surroundings before storing it. That helps a lot. I have never had any moisture inside the scope.

[Earl]

Im considering a complete strip and rebuild to remove as much internal moisture as possible now

[nightfisher]

Earl, have you had similar issues with the 180 pro?

[Earl]

Not at all which is odd i though it would be the same

[Dunkster]

I stuck my 6 in a room with a dehumidifier (actually portable air conditioner that didn't get used last summer ) for a couple of hours. Clear as a bell. Don't expect it'll last once I take it out back next...

[Earl]

It is starting to clear now, however the water marks from runs on the mirror are really bad, when it finally clears hopefully it will be usable.

[Phil Fargaze]

I`m glad I have noticed this thread because I have been getting some internal moisture in my C9.25 which looks to have left some marks on the inside of the corrector plate. It has lived in the observatory for a few months so I thought I had better bring it indoors for a dry out. I havn`t noticed any water marks on the mirror so far. For tonight I am going to leave a silica gel packet in the visual back. What Lars suggested seems like a good idea so I might try that as well.

[LukeSkywatcher]

Isnt there some kind of silica tube thingie you can buy to insert into the visual back of the SCT to draw moisture out?

Seems exspensive if all you have to do is insert a bag of it and tape it down so it doesnt fall into the OTA.

[Earl]

I have had a bag of silica inside the eyepiece end now for almost a week and its still dewy inside, but not as bas as it was. hopefully ill be able to clear it without a complete stripdown

[Leda]

I thought these cat scopes where hermetically sealed, no?

Does it get in via the rear tube just?

Is there any nitrogen purged cat scopes?

[damnut]

Hi Leda,

Cannot be hermetically sealed as you have to observe via the rear port. You can put a permanent filter in place as a dust stop though. I do not as a preference on my SCT.

[Earl]

An update:

The internal dewing did clear a little with a Silica bag in the end but not totally.

So I have bitten the bullet and took of the Corrector Cell, I have not taken the corrector out as there is no need to do so, (not sure why people do if they are not specfically cleaning it.

The dew as gone the mold was very fine white tufs which has all come off the flocking, im drying it all out internally and I have a hair dryer blowing cold air inside the ota to remove as much moisture as possible without using heat.

There are a few water marks on the mirror, but im not going to worry about that, from what i have read a mirror has to be really dirty to warrant cleaning, so ill leave it be.

Im going to leave it open for a few days before i put the corrector cell back on just to let it completely dry out.

I must say im much happier at this point than i have been for quiet some time.

[dweller25]

Earl, this sounds unusually damp - could it be associated with the flocking ???

[Earl]

Earl, this sounds unusually damp - could it be associated with the flocking ???

I have been pondering that, but it didn't feel damp to touch.

[Space Bat]

I keep mine in the kitchen - and it is relatively warm

I do have a home made dew heater which helps when observing - but after a while struggles to keep up if really severe.

One thing I do is put it nose down with a diag in and allow cold air within the tube to escape once inside as it warms up.

I do have silica as a back up but seldom find the need to use it.

[Caldwell 14]

Mine is in an Orion padded case under the bed, it can stay there, scary stuff this is! My heart goes out to you Earl, i'd feel sick