Exposure Latitude of Black and White Film

A while back I took a class in black and white film developing.  The instructor in the class talked about the exposure latitude of black and white film and how forgiving it is compared to other media such as slide film or digital images.  He made a comment at one point that really stuck in my head.  He said, "I'm not sure I'd be able to tell the difference in one stop between exposures."  At the time, I thought he was just kidding with us.

Fast forward a few months and I'm out with some photog friends doing some night photography in downtown Austin.  I was getting a shot of a high dynamic range scene of a lighted stairwell.  After several meter readings of the scene, I decided on an exposure of 8 seconds.  When I'm doing long exposures I usually have the camera in bulb mode and use a cable shutter release along with a stop watch app on my phone.  On this occasion I was using a cable release I'd picked up cheap somewhere and wasn't familiar with its locking mechanism.  I had been using it for a while that night and had no issues.  On my first exposure of the stairwell, I must have inadvertently hit the cable release lock because the plunger didn't release when took my thumb off.  I fumbled with the release for several seconds before I figured out how to unlock it, resulting in a exposure that was about twice as long as intended - a full stop difference!

Assuming I'd just blown the highlights to oblivion (as would surely have been the case with my digital gear), I grabbed another shot with the intended exposure time and moved on.  A few days later I picked up the developed film (Yes, I'm still not developing at home - yet!) and expected to see a mess of a negative for the overexposed shot.  I was very surprised to see that there was practically no discernable difference!  Here are the two exposures as scanned with no post processing:

Can you see much difference?  Neither can I.  The Fujifilm Acros 100 film I was using does a great job at reeling in the highlights and one stop wasn't enough to make any real difference in the shadows.  Had this been a digital exposure I'd surely have lost a lot of detail in the brightly lit stairwell.  With the black and white film, either exposure is workable and there was plenty of latitude in the scanned file.  My development class instructor wasn't kidding after all!

Here is the final image after a little post processing: