[paulmd]

IMO the most important characteristic that digital lacks is the "shoulder" of negative films. Once you exceed the target exposure of the film by several stops, it starts to take exponentially more light to further expose those areas. This translates into the ability to capture more detail in the highlights. It's not ideal - the tones of the film are certainly "blocked up", and color film may start to show color shifts (usually to yellow). It's better to hit the exposure properly. But with proper scanning or wet-printing technique (particularly split-filter printing) you can recover quite a lot of detail.

On digital - when the pixel goes to 255 light intensity, it's just gone. There's no way to recover data that isn't there. The Magic Lantern firmware has the ability to scan out lines alternating between high and low ISOs to capture blown-out areas, but it's not perfect either.

"Modern" films tend to be very well-behaved with regards to these kind of characteristics, actually. Acros 100 has virtually no reciprocity failure - for exposures between 2 minutes and 10 minutes you need to add 1/2 stop of light. I've recovered pictures off negatives with virtually no visible exposure. The tonality is great and the grain is virtually invisible even with Rodinal. The new Portra 400 is also extremely forgiving - you can get something workable up to about ISO 1600 or 3200 with standard processing, and if you push process (develop longer) it's even better.

[jrockway]

For color I mostly use Velvia 50 and Ektar 100 both which have poor reciprocity characteristics. When the meter indicates 10 seconds I expose for 20, and the results are pretty good: https://goo.gl/photos/uL3a8Ezf3NJfhdP49 Note that it's turning white lights green because of the reciprocity effects, but I kind of like that color. (The datasheet recommends a filter to correct this, making the exposure even longer. Given that I took this picture on a bridge, 40 seconds without a car going over and ruining the photo was going to be a stretch. Indeed, this picture is a little blurred because the bridge moved; my digital camera took a much better picture under these conditions.)

I have some Provia 100F which works to something like 160 seconds, I will try that in the future for long exposures.

I haven't tried the Portra films yet, as I mostly do landscapes, not portraits, and prefer Fuji's inaccurate colors for that application. (Ektar is a bit more muted color-wise, which yields a nice calming effect: https://goo.gl/photos/jMLY9UwS5Uwn2TQW7 )

One other thing: digital camera tend to get rated on shadow detail, not highlight detail, so their built-in light meters tend to "expose to the right", discarding highlights in favor of collecting more shadow detail. If you meter off an 18% grey card, a real light meter tends to give a shorter exposure than the camera's built-in meter, better preserving highlights. As someone who likes a well-defined sky, I'm betrayed by the camera manufacturers here. (But you'll of course notice it on the screen, and you can just turn the exposure compensation wheel to underexpose, and you're golden. It is not quite so easy with slide film, involving a lot of measurements and very careful spot metering. Therein lies the fun.)