My friend suggest me non-interlacing progressive mode to my Sony Nex-3N with low shutter speed and a lot of light and one camera photographing the player and one camera photographing the ball. Is there any ready made device to get the speed of tennis ball without manually calculating it from the pictures?
Traditionally, the speed of the tennis ball is measured with radars based on Doppler effect where the difference in pulses reveal the speed. This device costs about 100EUR and it is bulky to carry around besides a camera. So trying to get the speed in other ways:
Programmatically in Mathematica? Thread here.
Comparisons of shots
If you goal is to have measurements comparable to the professionals then you need to find a tool that is measuring the speed of the ball right after the racket hits the ball.
There are multiple tools commonly found in online tennis stores, but almost all of them measure the speed of the ball close to the net, which makes it not comparable to the "official" measurements of the pros.
It depends what exactly you hope to achieve with that measurement.
Is it for fun or to quantify progress or do you want to compare yourself to the professionals? I ask this, because this is a topic that was discussed endlessly in tennis forums I've been quite active in.