I noticed some COMA on my astrophotographs lately, that didn't show up last December. Stars near the borders of the image tend to form linear shapes directed towards the center.
My setup is: Skywatcher 80ED with a field flattener and a 450D canon to shoot. The OTA should in fact have some coma, but it should be reduced by the field flattener as it always did... somehow now it doesn't anymore.
I've filmed my attempt to focus a star both in the center of the image and on the borders, and you can download the videos here:
I am also adding a picture I took a couple of days ago, 300 secs of exposure at 400 ISO with decent autoguiding and high light pollution... look on the borders, it seems like coma to me!