Determining and Setting Exposure

Determining and Setting Exposure

Exposure is a fancy word for how bright your final image appears. The more ‘exposed’ a sensor is to light the brighter the picture. For an easy way to remember the components of exposure, picture me, sun tanning indoors beneath a skylight (don’t get too carried away).

## Aperture

The skylight itself is the aperture or “opening”. If I install a bigger skylight, more light gets through. Simple as that.

## Shutter Speed

The ceiling fan that sits between me and the skylight is the shutter. If I stop the fan with one of its blades covering the opening, no light gets through (in film a 0º shutter). If I stop it so the blades aren’t affecting the light, all the light gets through (in film a 360º) shutter. Shutter speed is simply how long I am exposed to the sun for. Aperture is fixed over time, shutter speed is all about time.

## ISO

I have sensitive white skin that is easily affected by the sun. It doesn’t take much light coming through to make a difference (perhaps this is why I’m sun bathing indoors). Replace me with my wife however and she’ll require a significant amount more of light to get crisped. This is the concept of ISO or the “sensitivity” of the sensor. If you have a highly charged sensor, ready and willing to take light, then you won’t need much to make a difference.

This ones easily for me to recall–all I have to remember is that “I is sooooo white”. The acronym refers to the “International Standards Organization” if you’re curious, but remembering that probably won’t help your pictures or your social life.

So how do these work together?

## The f-stop Scale

## Exposure for Video

The principle of aperture applies the same to photo and video. Shutter speed is a bit simpler in the video world. Since we usually shoot at 24 frames per second for a “cinematic look”, and the shutter opens and closes twice-per exposure, all you have to do is double your framerate to get the denominator (bottom number) of the appropriate shutter speed. So a 1/48 shutter works well for 24 frames per second. If you’re shooting higher frame rates then the same rule applies–a 96 frames-per-second shot benefits from a shutter-speed of at least 1/192.

## Exposure for Photography