[popo]

What is OSC?

OSC = one shot colour. Generally speaking, using a bayer pattern colour filtered sensor like that of most colour cameras. That way you need to have all wavelengths in good focus at the same time otherwise different colours will be blurred due to different focus points of each wavelength.

Colour astrophotography is also done by using a mono sensor and then using separate RGB filters in turn. Thus you only have to focus for each wavelength area at a time and don't have to worry about others. Of course this only really works if the subject doesn't change for long periods so you can align and recombine the image.