PHOTOOG Photography writings by Olivier Giroux


Photography 101: Motivation for Artificial Light

Ed: today I’m taking a slight detour on the 101 series.

You need a surprising amount of light to make pleasing color photographs. There’s little fundamental difference between the processes of color and monochrome photography, but our perceptions (and expectations rooted in history) for each differ much. We want color pictures to have accurate colors and smooth gradations, while monochrome photographs can be grainy and harsh and still please. Your camera and lens have to work much harder to produce the color results you want.

The process of capturing an image begins with illumination of the scene, where colored photons are bouncing around more or less wild depending on the light source. The lens picks up a fraction of these photons and transmits an even smaller fraction towards the sensor, for example at f/4 the transmission represents around 1% of the original signal. A monochrome sensor receives this weakened signal but a color sensor further discards roughly 75% of it in order to isolate base color components first. Photons that survive are then converted into electrons with relatively poor efficiency (around 10%) to form the digital image.

Simply put: you need lots of light to get a smooth image out of the camera because each stage discards much more light than it transmits. Of the light shining on your subject, only 0.025% can be traced to your digital color image. Some combinations of light sources and subject colors, like blue under tungsten light, form even weaker parts of the signal by an order of magnitude.

It’s possible to improve on the efficiency of your system in two main ways:

  • You could get a camera with a more efficient sensor. It’s likely that a better sensor exists out there and if you’re patient enough it’ll surely come to your brand and price range. You can be impatient too, but the cost/benefit ratio eventually becomes pretty poor at this level because prices almost double for every increment improvement at a given time.
  • You could get a lens that transmits a larger fraction of the light, with a larger aperture “f/-stop”. This is where many serious photographers spend their money, at least partly because lenses are longer-term investments, but the cost is often substantial. Photographers going this route eventually also sacrifice compactness, lightness and ease of use.

There is a third option if you’re more concerned about photography than engineering. It involves very little sunken capital, rather a good eye and some patience:

  • You could turn up the lights or otherwise augment illumination to amplify the source signal.

Two schools of thought in this area divide photographers evenly across the spectrum of experience. One camp restricts themselves to light from nuclear origin (i.e. sunlight) and reflections thereof. Sometimes they’ll accept man-made light if the photographer doesn’t control them (fixtures, street lighting). The other camp expands the meaning of “available light” to include any light that’s available at the time – altering existing lights or adding the photographer’s own light.

This the motivation for the use of flash in photography.  Two upcoming articles in this series will focus on the situations where each flavor of "available light" is appropriate, and provide tips to work within each philosophy.

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