- Take two flats.
- Raise the level of one of the flats slightly.
I am doing that in Pixinsight by using the Pixelmath expression $T+0.2.
- Subtract the other flat from this first flat
Again, in Pixelmath: Ha_01270-Ha_01269. (these are the names of the flat fit files).
- Measure the standard deviation in the middle.
In Pixinsight, I create a preview in the middle of the new image and with the Statistics process measure 5.1259e-003 = 328.06 DNA (*64000)
- Divide by sqrt(2) = 231.97 - this is the noise (or to be exact the quadrature sum of shot noise and read noise)
- Now subtract a bias frame from one of the two flats
- Use the same region (I drag and drop the preview that I created in step #4) and measure the average value: 6.1413e-001 = 39304.32 DNA (this is the signal)
- Now, gain = signal / (noise^2)
gain = 39304.32 / 231.97^2 = 0.7304
Tuesday, October 25, 2016
Estimating gain of my camera
I wanted to try out using the subframeselector script to assign weights to all frames. For that, I needed the gain of my camera. I can't find the data sheet from FLI anymore, but Richard told me a quick way to estimate the gain good enough: