Determining QHY8 Offset & Gain with MaximDL


Howto Determine the Gain & Offset settings for a QHY8 CCD Camera using MaximDL

I’ve seen many questions from people who have purchased a QHY8 camera concerning the correct setting of the Gain & Offset values. This short guide seeks to instruct people on how to determine those values using capture software, in this case, MaximDL v5.

After you click the “connect” button in MaximDL, a small window will appear which allows you to enter the camera’s Gain & Offset values. Based on what I’d seen others using, I started with a Gain of 1% and an Offset of 126.

The next thing you need to do is capture as short an exposure as possible (ie, a Bias frame) with the camera covered. Go to the Camera Control window and enter the settings you see below.

QHY8 1ms exposure instruction.jpg

Once you have taken the exposure (ie, pressed the “Start” button), the resulting image will be loaded into the window. The goal here is quite simple. You need to adjust the Gain & the Offset values and keep taking exposures until you achieve an average pixel value (as shown in MaximDL’s Information window) that is just below 1,000.

I played with my Gain & Offset values to see how close I could get to 1,000:

Gain = 1%, Offset = 126 – Average = 916

Gain = 1%, Offset = 127 – Average = 1021

Gain = 5%, Offset = 126 – Average = 968

Gain = 10%, Offset = 124 – Average = 886

I ended up settling on a Gain of 5% and an Offset of 126

QHY8 Bias shot.jpg

That’s really all there is to it. Once you have found the best values for your camera, remember them as they should not change.