I found trying to correct fall-off in Photoshop to be too much work. My Photoshop skills are such that the less work I have to do in Photoshop the better. I bought an expensive Schneider IIIB (?) center filter. I use it with my 55mm Apo-Grandagon, 65mm Super Angulon, and, when I had it, I used the CF on an 80mm SSXL.