Some earlier replies on where on the racket face the ball is first contacted:
Originally Posted by Chas Tennis
Stop Action with DVR. I looked at the clear high speed videos presented on the 2013 Australian Open by ESPN & Tennis Channel. I used my DVR to do stop action. Both ATP & WTA players. Only used videos that were clear with small motion blur. (Rejected double image effects probably due to unknown interlacing effects). Record keeping was poor, about 10-12 total.
These videos were usually winner highlights, where the players appeared to be in good position and intended to hit a very strong forehand. I don't believe that any were of shots that went out.
If the bottom/lowest frame edge of the racket were 0, the top/highest frame edge were 10 and the center line (handle center line extended) were 5 then
the ball hits were in the 4-6 range. I did not see any impacts that were way off the centerline.
Estimating impact spot, where 5 is the center line and the racket face is divided 0-10 bottom to top:
Li Na - 5, 6
Sharpova - 4, 5
Tipsaravic - 4
Some others also.....
I had intended to analyze more high speed videos shots just as Toly has done but have not gotten to it.
I had originally thought that pros deliberately or by trial-and-error practice were hitting most balls in the lower half of the racket face (say at 3 as defined above). Now I don't believe that. I intend to farther analyze videos for this issue as I come across them. The issue could be farther researched.
High Speed Video Analysis Issue- Racket is Rising Rapidly at Impact. One point is that for the current forehand with its rapid rise of the racket at impact, when you look at a high speed video and see ball impact, on the very next frame at 200-300 fps the racket will will have moved considerably higher. Not doing single frame analysis may produce a false conclusion as to where the ball was on the racket face at impact. Requires targeted high speed video with a clear view of the racket face, high frame rates >200 fps ?, a fast shutter speed for small motion blur, and observing ball impact on the strings. Any rolling of the ball on the strings makes analysis less accurate. Both the rapid racket motion up and the ball rolling on the strings might make the ball appear to initially hit low on the racket face if not carefully measured. I think that's what fooled me.
An interesting related question - Do I hit long and in the net because I am hitting high or low on the racket face - much more than the pros do - and the racket tilts while in contact?
This issue needs more work with high speed video that has adequate frame rates to see the ball movement during, say, 5 milliseconds of ball-string contact. 240 fps might not be enough. ?