Circular Gradient 294 MC Pro - Dew ?

idsteph

Please could you take a look at the attached images and perhaps let me know your thoughts.

I have noticed when taking flats via the Skywatcher 150 ED Triplet that there is a significant circular gradient on the FITS images concentrated in the center of the image. I have not noticed this whilst taking lights only when doing flats with my LED panel. I have two ASI 294 cameras one is set up permanently on the 150 APO (Camera 1), the other is set up permanently on the 9.25 Edge HD (Camera 2). I do not know which one is the newer or older.

Thinking there was a fault on Camera 1 I changed it out with Camera 2 – its performance was the same when attached to the 150 APO in place of Camera 1. I changed back to Camera 1 and conducted an experiment adjusting the cooler settings.

When I switched the cooler OFF the problem went away but only once the sensor had warmed back up so nothing to do with current. I switched the cooler back on and starting at plus 7’C the problem reappeared. I set the camera back to plus 10’C and the gradient disappeared.

Question 1 do you think this is condensation or dew forming on the sensor ? The ambient temperature during testing was 21’C the local dewpoint from BOM Australia Perth was 12.9’C with 65% relative humidity
Question 2 why do I not see the issue when the camera is on the 9.25 edge HD ?
Question 3 why do I not notice the issue whilst collecting light frames at night, is it because of the dark sky ?

Finally, the reason I pursued this today is that I noticed speckling whist taking Mono 8 shots of the Sun yesterday via a Solar Filter with the cooler set at my normal -10’C, see Grab – image 4

Grateful if you have any solutions/thoughts ? For now I will collect flats with the cooler off and collect Solar Fits/AVI/SER with cooler off also.

Tech@ZWO

hello
you can try to cool down the sensor slowly

you can cool the sensor to 5 degree and wait 5 or 10mins
then set it to your target temperature

Monsak

I have the same problem. If I cool the sensor below 0 degree, it will show circular area of bad pixel.

And the recommend to slowly cool down is not work, I wait for longer than 20 min at -5 degree but the circular defect is not disappeared unless I warm sensor above 0 degree.
I have sent question & my image to support@zwoptical.com but nothing come back.

paoloastrowebcam

hai risolto? ho esattamente lo stesso problema.
Paolo

bafio

Hello,
I have the same problem. I have use to shot at -10°C, but one night observing the flat i saw the same pattern of @idsteph and this disappear when i stop the cooler. I tried a lot of temprature and i noticed that the minimun temperature without this issue is +5°C. I tried to clean the sensor and the protective window but nothing, i tried to dry the dessicant tablets, but nothing, i tried to use the ZWO anti-dew heater strip but nothing. My last canche is substitute the dessicant tablets. What I can do?

Tech@ZWO

we recommend you slowly cooling the camera to solve the problem:

Before letting it cool down to target cooling temp, please keep it at 5℃ for 2-5 minutes, then cool it down to target temp
You also can refer to this guide to redry the desiccants.
https://astronomy-imaging-camera.com/manuals/How_to_clean_ASI_camera_and_redry_the_desiccants_EN_V1.2.pdf

bafio

Ok, thanks, I will try

Astro1

I have been struggling with this problem for a long while with my 294 MC pro , it manifests in a brighter central section in my images that varies in size dependent on FR . I have tried various scopes / C11 / 80mm refractor etc but all show the same effect .
Off the scope with a white card over the camera nose piece the flats look good , but when you look into the camera there is a circular misty patch in the centre of the ccd , it is on the chip not the window and gets worse the cooler you make the chip , two nights ago I tried again with the 80mm refractor with No cooling , it was chilly out but not cold or hot , same issue even on a short image . with a larger scope the effect is significantly worse , c11 flat attached . the frost is illuminated by the light cone , the size of which is dependent on FR