QHY8 Gradients

[RayH]

I have noticed a 15-100 ADU gradient, brighter at the bottom of the frame than the top, on my QHY8.  This gradient is observed on bias, dark, and light frames.  It seems to get worse at higher ambient temperatures.  Looking at old data I took a year ago (June 2008) the gradient was not apparent but it seems to be getting worse as time goes on.  Last winter it was only 15-20 counts but now it has been about 60-80 counts.  Letting the camera TEC operate for longer before shooting seems to help some.

Dark or bias subtraction does not always take care of this problem since it changes as the camera operates.  I use a 12V car battery for the field and a 12  AC power supply for home.  I have used different drivers but nothing seems to make a difference.

Is something going wrong with my camera?

Thank you for any help that you can give.

Ray

[QiuHY]

Hello,

      This is normal. Because the top pixels is readout at first. The buttom pixels is readout last. So that the thermal noise of buttom is bigger than top. The cooling will reduce it. If the cooling has problem maybe cause it heavy than before.
If all other condiiton like the gain is the same. The increase counts means the cooling is not so cold than before.

       Please check if cooling is good. Possible reason is :

1.TEC component get problems.
2.The thermal glue between TEC and the CCD lost.


Best regards,

[RayH]

Thank you Qui,

When this is the largest problem the ambient temperature is near 40 deg C.  The camera case becomes too hot to touch so my TEC must be cooling OK.  I will watch to see if it gets better once the outdoor temperature drops.

Thanks for your help.

Ray