anywhereSF

Day 27: January 27, 2014: Corona Heights

I don’t tend to post too much technical stuff, preferring to share the images and any interesting stories behind them, but that doesn’t mean I’m not thinking about the technical thingies. I am a scientist, after all, it’s kinda just how I operate.

Tonight was a little technical experiment on exposure and film vs digital, so gather round for a quick science lesson. You see, film has this property that digital does not, known as reciprocity failure. Essentially, the way photography is supposed to work is that the shutter is open for a set amount of time to expose the film or digital sensor to the correct amount of light to get an image.  If the exposure time is doubled, the film should collect twice as much light. However, it turns out that due to some complicated to explain physics and chemistry, this relationship breaks down in very low light. A digital sensor individually measures each photon of light that hits it, while film needs to collect energy from those photons to get a chemical reaction started. It works out that a certain threshold of energy from collecting several photons photons has to be reached to undergo the chemical reaction and leave an exposed point on the film. If the photons are too far apart in time, the energy can dissipate before the next one hits, and it ends up taking more light than you would expect to get the same exposure with film under the same settings in low light.

Assuming you’re still with me, I went out to test just how much extra exposure I would need at night. Taking a few shots perfectly exposed, underexposed and overexposed, according to the camera meter, I settled on this one as the best.  It turned out to be the most overexposed, at just about 2.5 times the expected exposure time. The others with shorter exposure times could be salvaged by the scanner, but came out super grainy. I find that even in better light, negative film likes to be overexposed a bit, where I almost always underexpose my digital night shots to keep the highlights from blowing out.

The corresponding digital shot with a modern Canon 6D below is massively higher in sharpness and resolution, which isn’t so unexpected since 400 speed film gets relatively grainy. I love the way the film handles bright highlights, though. Just like with the sun in yesterday’s photo, film just seems to have a different character. All of those signs, neon, all of those red lights on the buildings, they all stay colored with film, but they all seem to end up going white with digital. Maybe that’s partly the technology and partly my technique, but I dig the colors I get with film.

Lessons for the day: Everything has it’s advantages, get out there, try them all and see what works. Oh, and don’t be afraid of a little science 🙂

(Kodak Portra 400 in the Canon 650 metered for a 6 second exposure and shot at 15 seconds)