Previously, using an overcast sky, a white styrene 1mm, Plasticard, plastic sheet was placed over the front of the telescope and AstroDMx Capture for Linux was used to capture flat fields and calculate a master flat field. The flat fields were captured with saturation turned off, giving an effective monochrome image.
Master unsaturated flatfield
Note the pixel vignetting gives the opposite effect to classical vignetting as has been reported here previously. With classical vignetting, the centre of the image would be lighter than the peripheral areas. Also note, that the vignetting is asymmetrical.
This master flat field could have been used to do real-time corrections to the video stream in AstroDMx Capture for Linux, but in this case real-time correction was not used as a comparison of flat field corrected and uncorrected results was intended.
Four overlapping, 1000 frame SER files were captured with AstroDMx Capture for Linux so that the whole of the 98.3% waxing Moon was covered by the four resulting panes.
The best 500 frames of each SER file were stacked in Autostakkert 3.1.0 running in Wine; firstly without flat field correction and then with flat field correction, producing four uncorrected and four flat field corrected panes.
The unprocessed data were stitched in Microsoft ICE running in Wine to produce an uncorrected image of the Moon and a flat field corrected image of the Moon. The two images were then made into a blink animation to show the effect of Flat field correction.
Uncorrected vs flat field corrected, unprocessed data animation
The benefit of flat field correction is evident from inspection of this animation.
The flat field corrected image was wavelet processed in Registax 5.1 running in Wine and post processed in the Gimp 2.10
Flat field corrected image
Closer view
Flat fields need only be captured once and can be used many times.
With the correct procedures, the SVBONY SV105 camera is a very capable, low cost, lunar and planetary camera.
