DISTORTION IN BANDPASS FILTERED SIGNAL

A laser displacement sensor was used to measure the displacement of an object vibrating sinusoidal at 22 Hz. The output voltage of laser sensor is acquired using DSO. The same 22Hz signal is acquired with different time/div values. The data is acquired at different sampling rate. when we attempt to filter the 22Hz content of the signal using band pass filtering command in Matlab the outputs are quite different as shown in attached figures. Why the band passed signal outputs are distorted? How to find the optimum sampling rate so that the distortion of the band passed signal is minimal?