Ice on ccd sensor?

[speckofdust]

Hello all, came across this issue 3 nights ago. I think it is ice forming on the ccd sensor, but not sure why it happened as the outside temperature was about 10 degrees on average through a 3 hr imaging session (started at around 13 degrees). Turned on the cooler on the camera for a target temp of - 5 degrees which was maintained throughout.  after about 1 .5 hours the image started developing a weird shade at the centre. checked the objective, which was clear of dew. ( dew heater strap was on). looked down the scope and found a oval shaped area of fogginess at the centre of the CCD sensor, which I assumed to be ice. turned the cooler off and blew some warm air from a distance towards the camera and recommenced imaging after 10 minutes and after the fogginess was gone. The sub frame afterwards was good with no abnormal shade. So I presume this to be ice forming on the sensor, but its a bit weird, as I have not had this problem before and I have run the camera much colder at colder ambient temps.  Any comments/ advice welcome. Thanks  

equipment- sw E80 ED refractor, camera asi 1600mm with Baader LRGB filters on zwo electronic filter wheel

Edited November 15, 2020 by speckofdust
addnl info

[discardedastro]

Probably not ice but dew, and likely on the front of the sensor window rather than on the sensor itself. ZWO sell a dew heater specifically to warm the front of the camera, which may be all you need to add to fix this in future - alternatively a heater to wrap around the frontmost element in your imaging train.

If you can confirm it's inside the sensor window then you may need to consider dessicants - I'm not sure what the ASI1600 uses (if anything) on that front.