What is the Exposure Triangle?
The exposure triangle is one of the basic ideas in photography and once it is understood changing exposure settings becomes intuitive.
How does the triangle work?
Take an equilateral triangle and on each point place one of the following; ISO, Aperture, Shutter Speed. With each of these set right you will have a picture with the correct exposure. Once you have that first exposure you can then work out by making adjustments.
So, in making adjustments you can get the same exposure but with different settings?
In principle yes, with an exposure of 400 ISO, F22, 1/125 changing one of these settings would mean a need to change another. For example you want a lower ISO setting to minimize noise you would need to make adjustments to the Aperture or/and Shutter Speed. In lowering the ISO from 400 to 100 you would be dropping the exposure by 3 stops. To make a reduction of threes stops you could either lower the aperture/shutter speed by three stops or a combination of aperture and shutter speed. An example would be a setting of 100 ISO, F8, 1/125 or 100 ISO, F11, 1/60. In the first example I stopped the lens down by 3 stops from F22 to F8 going from F22-F16-F11-F8. In the second example I lowered the aperture by 2 stops and the shutter speed by one stop.
Why is this useful?
Knowing this is useful as it can be a way to quickly adjust your exposure to suit the needs of your image especially when it comes to adjusting the depth of filed. Aperture settings adjust the amount that is in focus with a small aperture (big number) like F64 the depth of field is wide with a lot in focus, whereas with a large aperture (small number) F1.8 the depth of field is very shallow with less in focus. If the exposure reading you get is like the one I used earlier 400 ISO, F22, 1/125, and for artistic reasons I wanted to have a shallower depth of field with a setting of F5.6 I can adjust two settings the ISO or the Shutter Speed.
Ok, how do I adjust these settings?
When you open up the aperture (take it from a large number to a small number) you are letting more light through to the sensor. This will overexpose the image if you continued using the same Shutter Speed and ISO. To correct the exposure you need to reduce the amount of light coming to the sensor by using a faster shutter speed, or changing the sensitivity of the sensor by lowering the ISO making the sensor more sensitive to light.
How do you know how much to change the settings?
First you need to count the number of F stops (aperture setting) you are moving. I do this using the conventional F-stops.
What do you mean conventional F-stops?
On modern digital cameras there are aperture settings that are not conventional apertures but a trait of the digital era. Conventional F-stops go up in a particular pattern 4, 5.6, 8, 11, 16, 22, where every other number is doubled.
So digital cameras have made some up?
In a way yes, they are more like half stops.
What if I changed the shutter speed not the aperture how do I count the stops then?
In a similar way to an F-stop there are shutter speeds that are not conventional as well. Shutter speeds change by dividing or multiplying your shutter speed by two for example; 1/500, 1/250. 1/125, 1/60, 1/30.
So what if I am on 1/80 for my shutter speed?
Then I would double it to get one stop higher at 1/160 of a second or divided it by two to get 1/40. When it comes to nonconventional apertures you can’t really double it to get the next stop up or divided to get the next stop down .A n aperture setting when doubles is equal to two stops up the same as when an aperture stop is divided it is equal to two stops down because the apertures double with every other number..
Back to my calculations taking my setting of ISO 400, F22, 1/125 and changing the aperture to F5.6 is a reduction of 4 stops. By lowering the ISO to 100 is a reduction of 3 stops. If I can’t go lower than 100 ISO then I still have to make a change of one stop. This means changing the shutter speed. We need it to let less light through, so the shutter speed needs to be quicker and 1/250 is one stop quicker.
What other situation could I use this?
The principle can be applied when you are stuck with low light conditions, in a situation when you don’t have a tripod and you need to use a medium length lens like 200mm, meaning you need a shutter speed of 1/200 and you also don’t want a very shallow depth of field so you settle with an aperture of F11 you can then use the ISO to make sure your combination can be met.
How can I really learn the exposure triangle?
This is one part of photography that you need to just know and the only way of knowing it is to practice and practice. Though practicing you have can get an understanding that can rapidly change your approach to taking pictures.
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