Now it's winter and my QHY8 keeps freezing over

[NocturnalOne]

Hi,

I thought I had a handle on my camera. I taped it shut, put silicone sealant around the connectors, sealed up the nose piece and dry out my camera with an EVA Dry in a plastic bag for days before going out. Worked fine all summer. Now it's winter and my CCD keeps frosting up. It disappears after maybe an hour or so but that's still not acceptable. Right now it's about -6C outside so I've unplugged the TEC in hopes of at least being able to take some pictures. The frost is still there, I guess I'll give it some more time.

So what do I do? Does desiccant even work when it's that cold? I thought perhaps the relative humidity inside the bag was too high at room temperature so I put the whole thing in the freezer. No ice on the sensor when it came out but apparently still plenty of moisture inside the camera.

I'm getting a little desperate here. This is the best time of the year to image and the ice is ruining it. Does anyone have a desiccant reference that says what the best strategy is for drying an enclosed space like a camera? Hot? Cold?

Thanks,

   Sander

[fetoma]

Sander,

Can you keep it locked up outside somewhere so the camera stays the same as the outside temperature? Worth a try maybe?

Frank

[NocturnalOne]

Frank,

I figured the freezer would take care of that. It's not that cold during the day. I could keep it powered all the time I guess but that's a bit drastic.

[QiuHY]

Hello,

       Normally speaking the freezing is easy happen in summer but hardly happen in winter. Espcially at -6degree. In this conditions the RH should be dry .What's the RH do you get?

And where is the frost? On front of the CCD sensor or on front of the optic glass?

Best regards,

[Gama]

If you have no power to the TEC, then it may be the way its moved from one area into the cold area.
This suggests a large differential temperature/humidity between ambient and camera body temp.
If its the front filter, then possibly use the heated window ?.

Theo.

[NocturnalOne]

Hi,

I wrote 'CCD keeps frosting up' which is exactly what I meant. The sensor itself, not the filter in the nose piece. I get nice tiny ice chrystals all over it. These slowly dissipate and disappear in about an hour or maybe two. Somehow storing the camera in a bag with an EVA Dry desicccant isn't drying the camera enough. I may have to bake the camera again to fully dry it out.

I was thinking of installing a small heater around the sensor so I can 'help' dissipate the chrystals when they form. Would that work? Clearly I wouldn't leave it on but just temporarily heat up the front of the sensor so that the ice can evaporate and deposit itself on the cold finger instead.

The other issue is that I don't really understand how desiccant works. Water moves into the gel because it's hygroscopic but doesn't realy bind with it because otherwise heating wouldn't drive the water back out. So to dry a camera as much as possible shouldn't I dry it cold? My experiment seems to indicate this doesn't work but I don't understand why.

Thanks!

[QiuHY]

Hello,

          The problem is the CCD sensor is cooled too fast. The cold finger has not catch all and CCD sensor get ice .Once the ccd sensor get ice , it is not easy to be disappear.
The best way is let the cold fnger freeze at first, then the CCD sensor will not freeze any more.  Normally speaking, once ccd sensor not get ice at starting, it will not get ice in future after cooling down.

You try this way:

1. Clean the cold finger at first.(Remove any oil on it. it is more easy to catch the water.
2. Slow down the cooling speed.


Best regards,

[fetoma]

You try this way:

1. Clean the cold finger at first.(Remove any oil on it. it is more easy to catch the water.
2. Slow down the cooling speed.

1) I suppose the camera needs to be completely disassembled for this?
2) How do you slow down the cooling speed with a DC101 that isn't regulated?

Frank

[QiuHY]

Hello,

     No need disassemble. Just take off the optic windows and clean the metal bard arround the CCD sensor.

    DC101 can not slow down it. But you can use some other method like let the camera cooling in a enclosed eviroment. The fan will not take much effect in this condition. After the cold finger take effects then take the CCD out. 

[NocturnalOne]

Hi,

Yesterday I refreshed the EVA Dry and let the camera dry for a day. I then plugged it in, first inside the house. No ice. I then moved the camera into the freezer and let it sit for an hour, with the power on the TEC. Still no frost. I will try again tonight and put the camera outside, see what happens.

It'll be a little hard to clean the cold finger as I put a piece of flocking material on top of it. There is space between the flocking material and the cold finger but maybe it is interfering somehow. The problem is that the cold finger reflect like a mirror and with the hyperstar that really isn't good. Let's hope I'm now ice free so I won't have to adjust the flocking.

Thanks,

  Sander

[QiuHY]

Hello,

        If there is flocking material covered with the cold finger. It may affect cold finger's capability to catch the ice. The cold finger must be fully contact with the air inside camera then it can take good effections. You can do a piece of black paper. With a retangle hole .This paper can be fixed in internal side of front case.

Best regards,

[NocturnalOne]

Hi,

if the ice issue has not gone away I will revisit the flocking. There should be space between the cold finger and flocking material but maybe there isn't enough. I know the piece of flocking material can be made a bit smaller than it currently is as it extends beyond the T2 opening.