The Shanghai Synchrotron Radiation Facility (SSRF) contains a 3.5-GeV storage
ring serving as a national X-ray synchrotron radiation user facility
characterized by a low emittance and a low coupling. The stability and quality
of the electron beams are monitored continuously by an array of diagnostics. In
particular, an X-ray pinhole camera is employed in the diagnostics beamline of
the ring to characterize the position, size, and emittance of the beam. The
performance of the measurement of the transverse electron beam size is given by
the width of the point spread function (PSF) of the X-ray pinhole camera.
Typically the point spread function of the X-ray pinhole camera is calculated
via analytical or numerical method. In this paper we will introduce a new beam
based calibration method to derive the width of the PSF online