How do I fix frost/condensation on sensor window?

RugbyRene (Rene) · #1 11-01-2021, 07:21 AM

Before I spend yet more money on this hobby I wanted to see if anyone else has had this issue and could help with a relatively inexpensive solution.

Last night I went out to image the Rosette nebula. I cooled my ASI294 down to -15 and took a 5 min test shot. When I looked at it I noticed a red/blue mottling in the centre of the image (see attached images). When I took the camera off the scope I noticed that a very small amount of frost/condensation had formed on the outside of the sensor window. I carefully wiped it off but it returned.

So has anyone else encountered this? I see that ZWO sells a dew heater but am unsure if it will work. Will a dew strap help or will the heat it generates compete with the sensor cooling?

Any help appreciated as I'd like to get out again tonight.

Cheers,

Rene

multiweb (Marc) · #2 11-01-2021, 09:46 AM

There's a cheap alternative that I've used for over a decade with my two QHY cams. Argon purge. Get a small canister from gasweld. That will last you for years.

RyanJones · #3 11-01-2021, 12:16 PM

Hi Rene.

You can use a dew heater strap. The sensor cooler is at the back and the window at the front is far enough away that they shouldn’t compete. Some of the newer cameras ( I recently bought an 071mc ) have a dew heater built in. I may also suggest not cool quite that low. There is normally deminishing benefits below a certain point, maybe -5 and as such it may not get cold enough at the front glass to cause the problem ? I can’t attest to Marcs suggestion but I’m sure if he’s been doing it for a decade that would work too.

Cheers

Ryan

RugbyRene (Rene) · #4 11-01-2021, 12:35 PM

Quote:

Originally Posted by RyanJones

Hi Rene.

You can use a dew heater strap. The sensor cooler is at the back and the window at the front is far enough away that they shouldn’t compete. Some of the newer cameras ( I recently bought an 071mc ) have a dew heater built in. I may also suggest not cool quite that low. There is normally deminishing benefits below a certain point, maybe -5 and as such it may not get cold enough at the front glass to cause the problem ? I can’t attest to Marcs suggestion but I’m sure if he’s been doing it for a decade that would work too.

Cheers

Ryan

Thanks Ryan,

Yeah I did think of using a dew heater strap (probably borrowed from my guide scope). I’ll also try not cooling so low and see hoe that goes.

Rene

ChrisV (Chris) · #5 11-01-2021, 01:08 PM

+1 with Marc. Argon.

Got some from a large liquor retailer (doubles as a wine saver). Every few months I argon purge my asi071 and microwave the desiccant (the 071 has an external connector with extra desiccant, so don't have to open up the camera).

I run it at -5C. When I'm too lazy to purge etc, I find that cooling to -5, then slowly cycling up to +5 and back down to -5 helps.

multiweb (Marc) · #6 11-01-2021, 04:14 PM

Quote:

Originally Posted by RugbyRene

Thanks Ryan,

Yeah I did think of using a dew heater strap (probably borrowed from my guide scope). I’ll also try not cooling so low and see hoe that goes.

Rene

Actually the warmer you are the more humidity is likely to be in the air in the camera. If you go low enough it will ice up. You'll dew up otherwise. In the end the name of the game is keeping the air inside your camera dry.

Cycling the camera cooling for instance because of a power failure or other issue will increase the chances of dew the second cooling around.

Nikolas (Nik) · #7 11-01-2021, 05:14 PM

There are desiccant tabs in the camera, you need to unscrew it, remove the desiccant and "recharge them in the microwave.

ZWO also sells a dew heater for the camera body https://astronomy-imaging-camera.com...nti-dew-heater

https://astronomy-imaging-camera.com..._desiccant.pdf

glend (Glen) · #8 11-01-2021, 05:32 PM

First of all Argon purging the chamber is not going to stop exterior condensation, and most good astro cameras have sealed chambers with dessicant protection inside. As your condensation is on the outside of the AR Window you need another solution. The ZWO adhesive heater element does work well, I ran one on my ASI1600MM-C for years. However, it was sized for the 1600 top case window, and I am not sure if that is the same size on your camera. I would email Sam at ZWO and ask him directly. You may also find the info on the ZWO Q&A pages on their website.

gb44 (Glenn) · #9 11-01-2021, 06:24 PM

Marc
Do you purge the refractor too?
Wondering also about dessicant in the refractor.
Would this work with a 12in SCT?

GlennB

multiweb (Marc) · #10 11-01-2021, 07:45 PM

Quote:

Originally Posted by gb44

Marc
Do you purge the refractor too?
Wondering also about dessicant in the refractor.
Would this work with a 12in SCT?

GlennB

This is only practical for a small volume of air that you replace with argon in a "sealed" environment (leaks via usb ports and power sockets) so you get rid of any moisture.

RugbyRene (Rene) · #11 12-01-2021, 07:23 AM

Went out again last night and tried the dew heater strap around the camera to fight this condensation..............complete waste of time. The dew/frost, whatever it is, was still there.

RyanJones · #12 12-01-2021, 09:18 AM

That’s annoying Rene. So is the frost/dew on the inside or outside of the glass ? I got the impression from when you said you wiped it off in your original post that it’s on the outside ? If so, then the dew heater needs to be on the nose piece of the camera as close to the glass as possible not around the body of the camera. That’s if I’m understanding right where you said you put it ?

RugbyRene (Rene) · #13 12-01-2021, 10:27 AM

Quote:

Originally Posted by RyanJones

That’s annoying Rene. So is the frost/dew on the inside or outside of the glass ? I got the impression from when you said you wiped it off in your original post that it’s on the outside ? If so, then the dew heater needs to be on the nose piece of the camera as close to the glass as possible not around the body of the camera. That’s if I’m understanding right where you said you put it ?

Hi Ryan,

Yeah it is on the outside. The dew strap I have is quite wide so I couldn't fit it properly. I've bought the ZWO dew strap which I've been told fits the 294 and works so I'll be giving that a try.

Rene

multiweb (Marc) · #14 12-01-2021, 10:55 AM

Quote:

Originally Posted by RugbyRene

Hi Ryan,

Yeah it is on the outside. The dew strap I have is quite wide so I couldn't fit it properly. I've bought the ZWO dew strap which I've been told fits the 294 and works so I'll be giving that a try.

Rene

By any chance is your camera pointing down? Are you imaging with a newt and the camera's on top?

RugbyRene (Rene) · #15 12-01-2021, 11:18 AM

Quote:

Originally Posted by multiweb

By any chance is your camera pointing down? Are you imaging with a newt and the camera's on top?

Nope. Sits on the back of a Esprit 100ED.

multiweb (Marc) · #16 12-01-2021, 11:43 AM

Quote:

Originally Posted by RugbyRene

Nope. Sits on the back of a Esprit 100ED.

ok. I had an instance with my QHY9 dewing up the front window when I sat it facing down on an EL panel to shoot flats.

I'd try purging it and put a sock in the front tube adaptors or a rag to keep it warm. That should do the trick.