Pushing?

Ilford Pan 400 shot at 1600, Bessa R.

I like pushing film, but usually I don't need to. ISO400 with a lens around f/2.8 should work fine for most situations. Pushing film does somewhat give you flexibility, but it's not really the film equivalent of just increasing ISO as digital cameras do. Nonetheless, it still gives great images, especially since sometimes it's a question of make and break when there just isn't enough light.

I've pushed film from ISO100 to 400, which inadvertent, since what happened was that I usually shoot ISO400 film, but then I loaded ISO100 film inside, but forgot to change the ISO setting, thus, I shot it completely at 400. I was quite perturbed, but the results weren't that bad, and in fact quite good.

Ilford Delta 3200 pushed to 12500, shot on my Seagull TLR

So, what does pushing entail?

Certainly, the first thing you'll notice is greater contrast in your pictures, poorer shadow quality as you step up the ISOs, more blown highlights, and greater grain, which may or may not be a bad thing. The implications of all these mean that your exposure must be more exacting, a bit like slides or digital.

Kodak Tri-X at 3200, Minolta X700.

Technically, this might imply that your pictures might be of lesser quality, but that doesn't suggest anything on the artistic aspect. Ultimately, I don't find that an image should be judged upon how much shadow or highlights it retains, but rather, it's aesthetic qualities are of primary concern. Technical quality simply complements aesthetics. An image can have two shades - black and white, but can still be amazing.