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It's funny, but one of the hardest things for me to "relearn" was that I could change ISO from shot to shot, depending on conditions. I grew up using film, and having to judge ahead of time what the lighting conditions were going to be like for the next 12, 24, 36 shots. Sometimes it was easy - if you were in the middle of shoot you already knew what the light was like.

However, sometimes you were packing film for a trip. Even weekend trip might entail bringing a dozen, two dozen, three dozen rolls of film. "Surely, you're not going to use all of that film?" To which you'd reply "No, but I don't know which kind of film I will be using, so I have to bring enough of each type. And don't call me Shirley."

Black and White or Colour. Slow film or fast film. Saturated colours or flat. Print or transparency. For the BW alone, you might bring Pan F, HP5, and SFX.

Being able to change the ISO on the fly has been a wonderful improvement, in my opinion.

However, I think we have also lost a lot by not having all of the film choices. Software can emulate many of the different looks we had with film, but it's still not always the same. When we changed films types, we were in actuality changing the sensor. Roll to roll, we could change the characteristics of the sensor. Modern camera sensors cover most of what film was seeing... but sensors can't see quite everything that film can see.
 
I typically stick to 400, film and digital. If conditions are right, I will shoot my DSLR at 100 for its advantages, but I like being able to use higher shutter speeds for increased sharpness in most situations and have found no distinguishable difference between noise levels at 100 and 400 in any practical application.

With film, I always shoot 400 for maximum versatility. With b+w, I like heavy grain, so I generally shoot HP5 and develop in 1:25 Rodinal to bring this out. Rodinal makes films faster than 200 especially grainy. If I really want ridiculous amounts of grain, I rate the film at 1600 and push 2 stops. Grain city!
 
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