Originally Posted by SystemicAnomaly
Not so sure that the image sequence from CharlieF is an optical illusion either. It's hard to say for sure. The camera position/perspective does not change. The ball appears to rising in this example. If anything, this camera perspective tends to disguise/minimize the amount that the ball is rising. If this was shot at an angle that is parallel to the court and close to the height of the contact, we would see that the ball actually rises more than this sequence of images would seem to indicate.
Let's look at the next photos of Stosur kick serves.
Figure 10. Sam Stosur Kick Serve
Unfortunately every picture produces an illusion. Nevertheless, it seems that the ball falls after contact even in case of kick serve. IMO there is no way it rises in case of twist serve.