Photons do not form diffraction patterns in low light conditions. Instead, the appear much as if they were scatter patterns and only evolve into diffraction patterns as the point source photon counts increase into the thousands.
This python program generates low light scatter patterns following the statistical rules for diffraction patterns. An animated GIF file shows how the pattern evolves as photons accumulate.
The "photons.py" script generates accumulation images, one for each new photon. The resulting photons.255.230.gif is an animated images of the sequence.