Understanding exposure can be truly baffling as a beginner photographer, and it’s nothing to feel ashamed about. Tons of beginner photographers struggle to understand the math behind exposure, and how to balance elements correctly. We’re here to break it down for you, and get you well on your way to mastering the exposure triangle!
What Is The Exposure Triangle?
The Exposure Triangle is made up of three elements that work together to produce a photo with the correct amount of exposure. Just to make sure we’re on the same page, exposure is the amount of light that reaches your camera’s sensor. It plays a crucial part in determining how bright or dark your photos are.
In the exposure triangle, If one element changes, the others must adjust to maintain this. Changing one setting can affect the others, which is why it’s important to understand what all the elements do, and how they relate to one another.
So, what are the three elements that make up the exposure triangle? Let’s dive in!
The Exposure Triangle: The 3 Elements
Shutter Speed
Shutter speed is the length of time that light is allowed to hit the sensor, and it is measured in seconds. With shutter speed, all you need to do is double the length of the exposure in order to double the amount of light.
For example, changing your shutter speed from 1/60s to 1/30s will add one stop of light, because the shutter will remain open for double the amount of time. Similarly, changing from 1s to 1/8s will decrease exposure by three stops, because from 1s to 1/2s is one stop, 1/2 to 1/4s is another stop, and finally, 1/4s to 1/8s further halves the time the shutter is open, providing the third stop.
Essentially, for more exposure (more light), you would want to slow your shutter speed to allow more light in.
Aperture
This one is notoriously tricker, so let’s break it down.
Aperture relates to the size of the circular hole in the lens that allows light in. The wider the hole is, the more light reaches the sensor. When you double the opening, you also double how much light is allowed in (aka increasing the exposure by one stop). Similarly, if you half the area, you half the light that hits the sensor, decreasing the exposure by one stop.
Aperture is measured in the value of ‘F-stop’. This is the ratio that relates to the size of the aforementioned opening. In a mathematical setting, it is equal to the focal length of the lens divided by the lens diameter.
F-stop values can look pretty confusing at first, and the numbers may not make sense due to the fact that small values correspond to larger openings.
If we take the ratio mentioned above:
f-stop = focal length/diameter
and rearrange it for diameter, you get:
diameter = focal length/f-stop
This essentially means that for any focal length, you can calculate the diameter of the aperture by dividing the focal length by the f-stop value. However, when you divide your focal length by a large f-stop number, you will end up with a small diameter – meaning that the area of the opening is therefore small. Flipping this, if you divide the same focal length by a small f-stop number, you end up with a large diameter, which equals a bigger area and more light hitting the sensor.
The f-stop numbers are not round numbers because to double the opening area, the f-stop must be divided by the square root of two (1.414). To half the area, simply multiply the f-stop by the square root of two.
If you’re a whiz at geometry, try it out to prove to yourself. Remember that the area of a circle is Area = (π/4)diameter2. Calculate the area of the aperture for a lens with a 50 mm focal length using various f-stop values. As you move up the f-stop scale, the areas should double.
ISO
The third and final element in the exposure triangle is ISO.
Essentially, ISO is the sensitivity of the camera’s sensor – although it’s a little more complex than that. Higher ISO values mean that the sensor doesn’t need as much light to generate the correct exposure. Lower ISO values mean that the sensor will need to gather more light to get the exposure right.
The ISO scale is infinitely easier than aperture, and is similar to shutter speed. Simply double the ISO for a one stop increase in exposure, and half it to reduce the exposure by one stop.
Example Of Balancing & Using The Triangle
If the above math is scrambling your head, take a breath. Let’s try another approach and put the triangle into a real-life shoot setting.
Let’s say you’re shooting outside on a sunny day. Your camera’s settings are:
- Shutter Speed 1/125 seconds
- Aperture f/8
- ISO – 400
… but, your image is overexposed, coming out super bright. Your choices to rectify this are:
- Smaller aperture to restrict the amount of light
- A faster shutter speed (let’s say 1/250 seconds) to reduce the duration of light hitting your sensor
- Smaller ISO (200, for example) to make the sensor less light-sensitive
And let’s say you’re shooting in low lighting. You would:
- Increase the aperture to let more light in
- Slow the shutter speed to lengthen the duration of light hitting the sensor
- Larger ISO for greater light sensitivity
You don’t have to have the exact math down, as long as you know what the changes you are making relate to, and balance the other elements of the triangle out to match.
What Else Does Exposure Affect?
Getting the correct exposure is important for taking great pictures, but how else does exposure affect the picture?
Artistically, the exposure triangle also makes a difference. Shutter speed controls motion blur, aperture controls depth of field and ISO controls noise, so it’s important to be aware of this when playing with exposure levels.
Here’s how to use these elements to impact your shots further:
- When you increase shutter speed, motion blur decreases. To freeze movement, choose a faster shutter speed – and a slower one to blur movement.
- Increasing aperture size also decreases the depth of field. For a blurred background (for a portrait, for example), use a larger aperture like f/2. For an in-focus background, smaller apertures like f/11 will work best.
- ISO increases mean more digital noise (or grain). This can be used artistically (in black and white images, for example) to give some grit. For clearer images without grain, use the lowest ISO available.
Final Thoughts & Cheat Sheet
We hope that this article has helped you develop greater understanding of the exposure triangle – including how they are measured, what they do and how they relate to each other. Don’t forget to use the cheat sheet above if you find it helpful!
With this information, you can better manipulate your image’s exposure, as well as making artistic choices a round motion, depth of field and noise. It can be a lot to take in but keep re-reading, practicing and writing out the triangle in ways that make sense to you.
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