QHYCCD

QHY294M Pro High Gain Mode Problems

Re: QHY294M Pro High Gain Mode Problems
« Reply #15 on: December 29, 2020, 10:31:44 AM »
From the image you post I believe the problem is solved. The satuarted level is close to 65000. Before this fixing the satuarted level is just about 30000. Much lower than the satuarted level.
Dear Qui,
Thank you for the reply but something is definitely not right.
Well the thing is that during my test the camera was pointed at a bright light source and neither 20 nor 100 sec was enough for complete saturation. Every pixel should saturate to ADC full scale if the camera is exposed for enough time.
Now we have the following in 11 MP mode: gain=0-1599 saturaion is complete; gain=1600-~2000 saturation level is only close to 65k but never complete regardless of exposition time.
« Last Edit: December 29, 2020, 01:04:35 PM by OnTheArrow »

QiuHY

  • *****
  • 5005
    • View Profile
    • Email
Re: QHY294M Pro High Gain Mode Problems
« Reply #16 on: December 31, 2020, 10:41:54 PM »
From the image you post I believe the problem is solved. The satuarted level is close to 65000. Before this fixing the satuarted level is just about 30000. Much lower than the satuarted level.
Dear Qui,
Thank you for the reply but something is definitely not right.
Well the thing is that during my test the camera was pointed at a bright light source and neither 20 nor 100 sec was enough for complete saturation. Every pixel should saturate to ADC full scale if the camera is exposed for enough time.
Now we have the following in 11 MP mode: gain=0-1599 saturaion is complete; gain=1600-~2000 saturation level is only close to 65k but never complete regardless of exposition time.


Hello, 

      I think  " Every pixel should saturate to ADC"    should not be right.  There is no rules to say that every pixel should satuarted to ADC.  The gain is just play the role that adjust the ADC input level to match with the signal.  You can adjust the gain to let it match, over-match or sub-match the ADC.

     Since 1600 is the HGC/LGC switch point. And both HGC/LGC has their own Gain adjustment.  So 1600 is the gain=0 for HGC mode.

     For gain = 0.  We always want to let the whole range of all pixel is under the ADC range.  For both CCD and CMOS, the pixel photodiode fullwell has a little difference. For example. Pixel(0,0) has a fullwell of 65000 . Pixel(0,1) is 66000. Pixel (1,0) is 64800. So it is a spread.  Normally we want to keep most of the pixel does not exceed the ADC range in gain 0.  So you will see a histogram near the 65535.

     If you keep on incrase the gain, for example, increae to 2000 . The amplifer ratio will increase and cause all the pixel saturate signal exceed the maxium range of the ADC. And you will see all pixel become 65535.

Best regards,
Qiu Hongyun

     
Qiu Hongyun