02-25-2019 09:10 PM
Keep in mind the title is "getting started" ... there's quite a bit not included in this article.
Part of the challenge of astrophotography is "image data acquisition" ... and part of the problem is "image integration and processing".
The author didn't mention a lot of the special types of exposures that are gathered (lights, darks, bias, & flats) as well as the image processing steps involved (special software that deals with image calibration, registration & integration ... this is fairly unique to astrophotography). Ultimately you get a combined "master" integrated image ... but that's just the starting point for the rest of the image processing & adjustment steps.
The cameras tend to be specially modified for astrophotography. You can use a normal camera, but the sensitivity will be weaker and the amount of exposure time will be increased. The Canon 60Da (the "a" suffix is for "astrophotography) was pre-modded by Canon to remove the normal filter and replace it with a more permission filter. Normal cameras are filtered so that the light collected will match the sensitivity of the human eye. But human eyes aren't equally sensitive to all wavelengths across the visible spectrum. We are not especially sensitive to the "reds". 90% of the normal matter in the universe is Hydrogen. The dominant emission wavelength for Hydrogen is mostly the Hydrogen alpha wavelength (656nm). Human eyes are only about 20-25% sensitive to this. Normal cameras gradually ramp up the blocking starting at around 550nm and increase it block 100% by the time they get to 700nm (the end of the visible spectrum on the IR end). At 656nm, a normal camera blocks around 75-80% of the light. But this means you have to run much longer exposures to collect this light. Modded astrophotography cameras replace the factory filter with a much more permissive filter.