Plate Solving is precisely what the name says: you take a photographic plate, note down the position of stars in the plate, create asterisms and compare with a catalog of known asterisms, with known star coordinates, and solve for the coordinate of the center of the plate.
Given an exposure (a "plate") the first thing you need to do, before finding the asterisms, is to identify what a "star" is. To do that, most systems will reject saturated pixels, and they will also reject something so bloated (unfocused) that they do not look like a star.
So, you need to start with that. Make sure that no more than one or two of the stars in the frame are saturated. ASIAIR will not recognize anything that is saturated as a star.
This is important. Use only as much exposure as needed. Typically one to five seconds is sufficient, unless you have a very narrow band filter that does not admit enough photons.
You want to identify asterisms of brighter stars, since the catalog of asterisms may not even include dimmer stars. So, make sure not many bright stars are saturated, and thus get thrown away. Sometimes, you cannot avoid having a star or two (for example, having Vega inside the frame) saturating. That's fine. Just don't expose so that more than a couple of stars in the frame are saturated.
Equally, if not more, important is to have tack sharp focusing (which also helps with signal to noise ratio). Use a Bahtinov mask to focus the exposure before even attempting to plate solve. ASIAIR will reject blobs that have FWHM that is over some amount. Try to get the average FWHM to be below 3 pixels if you can.
Make sure the plate sees nothing but the sky. Clouds, tree branches, chimneys will all block some stars and not others, and that will change what asterisms the plate solver assembles.
A lens with horrible geometric distortion (a fisheye lens is an extreme example) will also confuse the plate solver.
So, focus, focus, focus, and expose for no more than necessary.
Chen
