Three MTF machines are compared:
a lloir4 scan of spread function (ODETA V). With this method the Fourier transformation of the spread function is done instantaneously by the PM tube integrating over the image. The microprocessor tasks are limited to A/D conversion, scan control, normalising and data print out.
b Slit scan of spread function. Using this method the spread function itself is loaded into the computer memory (N samples over the x axis). After data acquisition the computer starts an FFT algorithm to produce the MTF.
c Knife edge scan of spread function. With this method an edge instead of a slit is used. The rest is the same, but the signal is the spatial integral of the spread function. Let A = total number of photons in spread function during the measuring time, and N = number of samples along x axis (for ODETA, N = 400).