When photographing astronomical objects during the day using an astronomical camera, a problem may arise with the visibility of dust on the sensor. Dust, as well as uneven illumination of the matrix, can be easily eliminated using flat field frames. During calibration, the original frames of the Moon are divided into a flat frame, so the output is a frame without dust. This technique can be useful when photographing planets (for example, Venus) during the day.
SHOOTING AND PROCESSING ALGORITHM
1. Shoot a video of the Moon of the required duration.
2. Move the telescope a little to the side so that the Moon goes out of sight. Do not touch the focus and position of the camera.
3. Adjust the white balance in the camera settings so that the sky turns from blue to colorless. Look at the histogram, the three peaks should be approximately at the same level. If necessary, increase the shutter speed; the histogram should be filled approximately 75-85%. If shooting through SharpCap, when adjusting White Bal (R) and White Bal (B), you can simply press the Auto buttons on the right (activate), and then press them again to fix the values. Record a video with a series of flat frames; in the future this will be the main frame of a flat field (flat). I usually record 100 frames.
4. After shooting, drag the flat video into Autostakkert, click Image Calibration>Creat Master Frame, give the file a name (for example, flat). Wait a little. After a short processing, a flat file will appear in the program folder (see video below).
5. Drag the video with the Moon into the Autostakkert window. Click Image Calibration>Load Master Flat, select the created flat file, it will be automatically applied to the video, dust and uneven illumination should disappear.
6. Next is standard processing and adding sharpening.
Of course, flat frames can be shot not only against the sky, but also against another uniform light source (for example, a white wall, laptop screen, etc.). In a similar way, you can remove dust when photographing the Moon at night.