Monday, 20 August 2012

Understanding Exposure – The Exposure Triangle

Exposure triangle is all about the three elements of photography that determine the correct exposure for an image and their inter-relationship. The three elements that we speak of here are Aperture, Shutter Speed and ISO. They all have their respective contribution in deciding the final outcome of the picture.

The Exposure Triangle
The Exposure Triangle
Aperture controls the size of the lens opening there by controlling the amount of light that gets through for any given duration. It has direct bearing on the depth of field of the resultant image.

depth of field
Photo By Toomanytribbles

Shutter Speed controls the duration of the exposure (exposure time – the amount of time the shutter is open letting in light). Shutter speed affects motion blur or how motion is captured in a picture.

shutter speed
Photo By Expressmonorail

ISO is the measure of sensitivity of the digital camera’s sensor towards light – ISO affects the noise levels in an image.

Photo By Seanmolin

Aperture in 1 stop increments:              f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/22
Shutter speed in 1 stop increments:     1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000
ISO in 1 stop increments:                     100, 200, 400, 800, 1600, 3200, 6400, 12800

The three elements have a direct bearing on the values of the other two elements, if the aperture is reduced by one stop then either the shutter speed is to be increased by one stop or the ISO needs to be reduced by one stop. If for example f/8, 1/250 and ISO 200 indicate a correct exposure and if we reduce aperture from f/8 – f/5.6 then we should either increase shutter speed from 1/250 – 1/500 or decrease ISO from 200 -100 in order to maintain the correct exposure.

Every correct exposure is actually a combination of an Aperture and a Shutter speed at a given ISO setting. And we could get the same correct exposure by using various combinations of these three variables. It is said that at any given ISO, there are at least 6 different combinations of shutter speeds and Apertures, creating six photographs with six different effects or feel. Although one may argue that there are many more combinations possible, it is possible only theoretically and is not very practical in field.

Let us try to understand clearly the above mentioned point and in order to do it just imagine we are out in the wild shooting a waterfall after sunset. Imagine the camera reads a shutter speed of 4 seconds at f/11 and ISO is 100.

So what other options do we have?

Aperture                Shutter Speed

f/4                            ½ second
f/5.6                        1 second
f/8                           2 seconds
f/11                         4 seconds
f/16                         8 seconds
f/22                        16 seconds

Even though some lenses allows shooting at narrower apertures; at f/22 we reach the narrowest aperture setting of most of our lenses. We have now captured 6 different frames of the same scene with 6 different combinations of shutter speed and aperture. Remember we have a correct exposure in all the six shots, but in each of these 6 shots the motion captured will look radically different and so does the depth of field.

As a creative photographer, your choice of Aperture and Shutter speed should be influenced by the final effect that you would like to produce in your image, think about what do you want to convey,

Do you want to freeze action? – Fast shutter speeds – 1/250, 1/500, 1/1000
Do you want to convey a sense of motion, panning, zoom blur? – Slow shutter speeds – 1/60, 1/30, 1/15
Do you want the image to stand out from background? – Wide apertures – f/1.4, f/2, f/2.8, f/4
Do you want the whole of the image to be in sharp focus? – Narrow apertures – f/11, f/16,f/22

Getting the most out of it

It takes a lot of practice before one becomes a true master of exposure and even then, there won’t come a time when he/she could just look at a scene, visualize an effect, set the exposure, click, and get the perfect shot and walks away. Every shot will need to be fine tuned, the settings tweaked again and again to get to the desired result. So keep experimenting with different settings, if you find handling all the three elements simultaneously a bit strenuous; put the camera into one or the other creative mode like shutter priority or aperture priority and let the camera handle the other two elements. You will eventually get better.