During convolution of synthetic images with various PSFs we need to consider if flux is conserved. We calculate such images for a range of alfas and show here the difference in percent of the total flux of the image relative to the ideal image.
-1.6768524 % out1p4.fits
-0.060953825 % out1p6.fits
0.014277556 % out1p8.fits
0.027423956 % out1p9.fits
That is, in an image convolved by the broad PSF with alfa=1.4 1.67% of the flux is lost, while only 0.03% of the flux is changed when convolving with a PSF with alfa=1.9 (the narrowest possible).
The loss (and gain) in flux is not understood yet – but is perhaps related to clipping (in the case of the broad PSF) of halo when the images are padded 3×3 in order to perform the FFT, or roundoff (narrow PSF – many values are rounded below 1 to 0).