What is exposure though?
The technicalities of exposure are rather convoluted and a bit mathsy, however the end result is that exposure refers to how bright or dark your photo is due to the amount of light that is recorded by your cameras sensor. A properly exposed photo should (normally) resemble the brightness of the original scene. A poorly exposed photo will either be too dark or too bright and may contain areas that are so dark or bright that they contain no detail (know as blown out). So how can we control the exposure of a photo? That is where the exposure triangle comes in.
What is the exposure triangle?
The exposure triangle is a useful way of describing the relationship between the three aspects of exposure. Each corner of the triangle represents one of the three variables, aperture, shutter speed and ISO. Adjusting just one of these will make the photo darker or brighter and will change the appearance of the photo based on what you have changed. E.g. using a longer shutter speed will introduce motion blur to your photo but also make the photo brighter (increased exposure) due to more light hitting the sensor. The easiest way to understand it is to see the picture.
So why is understanding the Triangle the end of auto mode?
The workings of the exposure triangle are all your camera’s ‘brain’ is using to achieve a correct exposure. Now that you know how it works you can take over and make the decisions for yourself. What can you do that your camera can’t? You can make creative decisions to get a better output, your photo. A few scenarios (it probably helps if you understand the affect of shutter speed, aperture and ISO before you read this so follow the links)
- You are at a wedding in a church, the light is dim. You have to hand hold your camera as you don’t have a tripod. Therefore you have set your shutter to 1/60s, the min you can hand hold at. You want a small aperture for a large depth of field to get the whole church in focus, you pick f/8. You take a photo and its too dark. Using the exposure triangle you can see than you can record more light by increasing your ISO. This will create more noise in your photo but you will still be able to achieve the DoF and sharp shot you require. If you decided the noise was too much you could use a larger aperture but this would cause less of the shot to be in focus.
- You are at a waterfall in the woods. You want to create silky smooth water with motion blur. You put your camera on the tripod, to reduce the amount of light entering the camera you use the smalled aperture f/22 and the lowest ISO, 100. Using the exposure triangle we can see the only way to let enough light into the camera is to use a longer shutter speed (which we want). This gives us a shutter speed of 1/2s, perfect for blurring the water.
What is all this I keep hearing about ‘stops’ then?
A stop is a term that photographers use to describe the amount of light, the exposure value. You can adjust the amount of light recorded using either of the corners of the exposure triangle. ISO 100 will record 1 stop less light than ISO 200, a shutter speed of 1/125 will record 1 stop more light than 1/250 and finally an aperture of f/5.6 will record one stop less light than f/4. Practically all this means is that you can achive the same brightness of photo with different combinations of settings
1/60, f/11, ISO 200 and 1/1000, f/2.8, ISO 200 will both achieve the same brightness of photo but the depth of field will be different.
What if I can’t change my settings?
If you need 1/60, f/2.8 and ISO 400 to achieve the photo you want but its just too dark you do have another option. Right at the centre of the triangle. Change the amount of light, the flash being the most frequent example of this. The other way you can use filters to reduce the light.
What next – try it out, take the camera out of Auto mode and see what happens. In future posts I will talk about the modes dial and exposure compensation as ways of putting the exposure triangle to use.