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 Post Posted: Thu Dec 14, 2017 2:43 pm 

Joined: Thu Dec 14, 2017 1:08 pm
Posts: 1
I just bougt the ASI294MC and the first thing I did was to take some bias frames. I downloaded the frames via USB3 port on to my windows 10 PC with SGPro. Gain was 120, temp -5°C. When opening the frames in Pixinsight and applying the STF (screen Transfer Function-stretch) Some brought horizontal banding becomes visible on all of the bias frames but not always on the same place in the image. So the sensor or cooling can't be blamed. To take a closer look I made 30 Bias frames and integrated them.
After integration I cropped from the middle a 2048 x 2048 square. From one of the bias frames I did the same crop. Then I subtracted from the cropped bias frame the cropped integrated bias frame and did an FFT (fast fourier transform) using the FFT module from PI. The result shows me an image with a vertical bright line in the middle. If the pixel distribution of the bias frame would have been Gaussian I would have only a bright point in the middle of the image. The vertical line seems to tell that there is a high frequency component in the downloaded bias frames. Maybe a badly shielded clock frequency???
The method used is described by QSI in their article: Interpreting Fourier transforms: link:
Can you tell me what your interpretation is of this phenomenon?
Attached the FFT and one of the bias frames.
Kind regards

File comment: FFT analysis of bias frames
DFT_magnitude.jpg [ 130.86 KiB | Viewed 31 times ]
File comment: single bias stretched with STF in PI
Bias USB3_0001.jpg
Bias USB3_0001.jpg [ 71.85 KiB | Viewed 31 times ]
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 Post Posted: Fri Dec 15, 2017 4:13 am 
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Joined: Thu Feb 21, 2013 2:51 am
Posts: 2352
sorry to say there is such noise with 294
almost all CMOS cannot have very clean bias frame as CCD
but this is not very serious problem
because these noise is very small and can be averaged by stacking
or covered by sky glow

ZWO Founder
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SuZhou China

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