  The combined PSF of the BFI and the SOT onboard the Hinode spacecraft is
investigated. Observations of the Mercury transit from November 2006 and the
solar eclipse(s) from 2007 are used to determine the PSFs of SOT for the blue,
green, and red continuum channels of the BFI. For each channel large grids of
theoretical point spread functions are calculated by convolution of the ideal
diffraction-limited PSF and Voigt profiles. These PSFs are applied to
artificial images of an eclipse and a Mercury transit. The comparison of the
resulting artificial intensity profiles across the terminator and the
corresponding observed profiles yields a quality measure for each case. The
optimum PSF for each observed image is indicated by the best fit. The observed
images of the Mercury transit and the eclipses exhibit a clear proportional
relation between the residual intensity and the overall light level in the
telescope. In addition there is a anisotropic stray-light contribution. ...
BFI/SOT operate close to the diffraction limit and have only a rather small
stray-light contribution. The FWHM of the PSF is broadened by only ~1% with
respect to the diffraction-limited case, while the overall Strehl ratio is ~
0.8. In view of the large variations -- best seen in the residual intensities
of eclipse images -- and the dependence on the overall light level and position
in the FOV, a range of PSFs should be considered instead of a single PSF per
wavelength. The individual PSFs of that range allow then the determination of
error margins for the quantity under investigation. Nevertheless the
stray-light contributions are here found to be best matched with Voigt
functions with the parameters sigma = 0."008 and gamma = 0."004, 0."005, and
0."006 for the blue, green, and red continuum channels, respectively.
