Quote Originally Posted by Dave Gooding View Post
Thanks. what sort of range can a film sensibly cover? I did run a series of 20 or 30 test exposures on Ilford HP5 as part of a calibration exercise (to calibrate a sensor against which each unit is checked and adjusted). I measured the negative intensity and plotted it against exposure. It follows an S-curve with a roughly linear region of +/- 4-ish steps in the middle but there are measurable intensity differences between consecutive exposures even at 10 stops away from the nominal, although to the eye these extreme ones have no discernible difference. Would you really operate the film at these extremes?
If you used a single development time for your negatives, you haven't yet actually tested how long a subject brightness range (SBR) the film can usefully record. There's a whole body of technique around how to manipulate exposure and development, in light of a given film's sensitometric properties, to optimally capture any given SBR.

There are special film/developer combinations, such as T-Max 100/DI-13, and techniques, such as David Kachel's SLIMTs, that are designed to tame SBRs well beyond 10 stops to make them printable on enlarging paper. If you're going to scan rather than print directly to silver, high-DMax/long-straight-line films like T-Max 400 can capture ridiculous SBRs that, with considerable effort in digital manipulation, can be reduced to something that can go on paper.

No need to dive into the details of all that if it's not your primary interest. The take-home remains that yes, as a photographer I can use as long a brightness measurement range as you can give me.