Comment by alephnil

You would need a frame rate higher than the Nyquist frequency of highest harmonic you want to capture. Since the fundamental frequency of the lowest pitch sting is 83.4 Hz, and you want to capture up to the fifth harmonic (at 83.4 Hz * 5 = 417 Hz) and double that to get the Nyquist frequence, so at least 834 fps. So you would need a high speed camera with 1000 fps to capture the real vibrations.