This is a frame of Ilford PanF+, shot on a Hasselblad 503cx with a 50 f/4 Distagon FLE.
I stacked two 3-stop cut filters (a 3-stop ND and a red filter), for a total of 6 stops of light loss. I metered the emerging shadows (Zone III) at EI 50 (PanF+ has a nominal ISO of 50), f/8, 1/15, using a Sekonic L-508II in 1 degree spot mode (you don't use an incident meter for negative film, do you???). From there, I added 6 stops, giving a nominal exposure time of 4s.
This is where it all went wrong. Without immediate access to the Ilford reciprocity failure chart for PanF+ (which is, in fact, available here...I must have forgotten about the miraculous communication device sitting in my pocket), I estimated the additional required exposure to be about 3 stops, or an exposure time of around 30s. Then I decided to add an additional stop just to be safe. So a 1 min exposure for a metered 4s exposure
As you can quite clearly see from the linked chart, the actual adjusted exposure for a 4s exposure on PanF+ is roughly 1 stop, or ~8s. Thus, my 1 min exposure is something like a 3 stop overexposure.
But wait, there's more.
Remember that I metered the emerging shadows. The meter, of course, tells me the correct exposure for Zone V, which means I actually needed to further reduce the exposure by 2 stops, in order to place the metered shadow area into Zone III. I don't generally do this with most films, but PanF+ is notoriously contrasty, and so I like to throw a bit of extra light into the shadows (I sometimes rate it at EI 25, for the same reason). So my metered 1/15 (Zone V) should have been 1/60 (Zone III), and thus my adjusted exposure should have been 1s, which needs barely any reciprocity compensation at all (as per the linked chart).
The bottom line is this: the film was over-exposed by somewhere between 3-5 stops. Processing was in Xtol with no push/pull (i.e. developed to EI 50). The result?
Even with the high dynamic range of my Nikon D800, I wasn't able to save those highlights (note the HUGE vignetting; that's from stacking the 2 filters on top of a UV filter AND a bay60 to 67mm adapter). Basically, I fucked this exposure up. Bigly.
I post this flaming hot mess of a photograph merely to make the point that, despite what you may have read, you cannot simply throw gobs of light at every type of B&W film and expect the highlights to hold. What may work for Tri-X does not work for PanF+, or, for that matter, for many other films.
I didn't set out to (re)make this point, but (re)make it I did. I always knew my incompetence and lack of patience would pay off.