After much trial & error in taking pan shots of race cars, I have learned I was sub - consiously 'stopping the pan' at the moment I pressed the shutter button. Once I reprogrammed my myself to maintain a constant sweep movement regardless of when I pressed the shutter button, my pan shots improved greatly. I also learned about zone focus, where the camera is focused on a stationary object just behind or just in front of where the photo is set. Then I don't try to re - focus as the moving object passes. With today's digital SLRs this may require disabling the auto - focus feature.