I haven't tried post-flashing, but pre-flashing makes a HUGE difference when pushing the crap out of films.
My example is with colour film, Superia 800 exposed at 12800.
FTR, my pre-flash method was double exposure, I held a tissue over the lens and metered through that with camera meter, and determined the pre-flash amount. It was with a Canon AE-1, I used that 'trick' of winding tight the left hand spool and holding it, while pressing the rewind button then gently advancing the frame advance lever.
C-41 @ 6 minutes.
12800 no pre-flash
Superia 800 @ 12800 no preflash by athiril, on Flickr
12800 with 'zone 3' pre-flash (Zones 1 and 2 did nothing essentially, all of a sudden at this point density suddenly jumped up, contrast improved, shadow detail increased).
Superia 800 @ 12800 Zone 3 preflash by athiril, on Flickr
Last edited by Athiril; 10-15-2013 at 08:05 PM. Click to view previous post history.