Film is typically used at the speed/ISO/sensitivity it was made for. 200, 400, 800, and so on, but you can push film to take pictures in settings it wasn’t necessarily designed to do so in. These shots are all from a roll of expired Fujifilm 200 film, which at 200, is made for direct sunlight and could also be used with a flash. The lower the ISO, the lower the sensitivity of the film, the more light you need to have coming into the camera in order to produce a clear image. Pushing film while shooting (cause it can also be done in development) is setting the camera’s ISO higher than the film in it.
The above shots were pushed to 400, 400, 800, 3200, and 3200, respectively. Pushing film isn’t the hardest thing in the world but it does call for some quick math if you’re doing it in your head and not using something like a chart or app. For example, the second shot in the subway corridor, I set the camera up at ISO 200, aperture was 2.5 (lowest on the lens) and my shutter speed 1/30th of a second I think but when I checked the light meter it was barely lifting up and indicating the shot would be really underexposed so I moved the ISO to 400 and the needle went a hair above where it previously did. I could’ve pushed to 800 but I wanted the image to be a bit dark.
If you’re wondering why the last two pictures have a slightly blown out look, I’m not entirely sure, myself. I think it’s a combination of using expired film AND pushing it well beyond what it was designed for along with a slower shutter speed. I think those were both 1/15th of a second. If I made any mistakes in this, feel free to correct me and I’ll edit it but I’ve only shooting film for a little over a month so I’m still very much learning the ropes.