So Adrian, I get that you probably won’t need contrast index approaching 0.7 unless someone brings you woefully underexposed film.
You might adopt 0.5 or 0.4 (probably not 0.4). But most of all you aren’t tied to
ASA or Zone System... You get to make the target what’s best for you.
That’s all I wish for all of us.
Yes, but I do also want to make negatives that could reasonably be printed in a darkroom, so it’s about finding that balance that makes best use of the scanner tonal capabilities while still being reasonably nice for analog prints. If I can make it work for both, all the better. For normally exposed negatives, that’s easy, find the time that gives N development for zone system and make a curve that linearizes as much of the toe and shoulder as possible for that time.
It’s when you get into way under or way over exposed film, or even worse, a roll that’s both that things kind of turn sideways. Simply running at n time isn’t doing me or the client any favors, and leads to getting a client who probably won’t return because I didn’t deliver good results.
For most digitization of negative film, less contrast is better as long as you’re not wiping film speed off. The first 0.3 log units of film density above film base plus fog eats half (!!!) of the discrete tonal values you’re going to get out of the scanner. In Stephens case with his Howtek 4500, the PMT ADCs are 12 bits. That’s 4096 discrete tonal units, of which, the first 0.3 log units of density above film base plus fog eats 2048, the next 0.3 eats 1024, and the next 0.3 eats 512, leaving 512 discrete tonal units to handle all the density above 0.9. That’s not very much, as every time you add 0.3 units of density you suck up half the available tonal values left. If you want to avoid visible posterization, you need at least 24 discrete tone values per stop of exposure. If you developed to 0.5, that means each 0.3 log units of density are roughly 2 stops of exposure, which means as soon as you hit 48 discrete tonal units per 0.3 log units of density, you’ll start to see posterization when it’s linearized. For a howtek 4500 that spot is film density 1.8 to 2.1 log. Can you do more than that? Sure. Will it look good? No. The highlights will be chunky and noisy.