If you are serious about your photography, any genre, you need to learn the "exposure triangle" and get out of auto-mode to start expressing your creativity your way.
The literal meaning of "photography" is writing with light, so how you manage the light (exposure) is synonym with how the artist uses the brush to apply color to the canvas.
There are zillions of articles and videos explaining in highly technical detail this topic. I, on the other hand, am more practical and skip the science. I go straight to the visuals to demonstrate the various terms.
Let's start from the beginning. What is "exposure"? The term exposure refers to how much light is being captured in the photo. Ideally, there's just enough light to show details in the darker areas of the image as well as the details in the brighter areas. Our aim is to avoid the extremes (totally back or totally white).
Notice the dark hills in one image and the bright areas of the sky in the other, detail is lost.
When details are lost, it is said to be "under exposed" (dark) or "over exposed" (white).
In the old times, photographers carried a cheatsheet to calculate proper exposure; Nowadays it is easier because the camera has a meter similar to the one in this image that indicates the exposure level as you set the controls.
Look for it in the viewfinder and/or the options of the live view LCD. The meter will show numbers going from negative to positive. Proper exposure sits right at the middle, on 0. If the needle is to the left of the 0, the photo will be darker. If the needle is to the right of the 0, the photo will be brighter. You want to avoid the two extremes and aim to get closer to the middle, understandably a night scene will be to the left of the 0 while a sunny beach day might be to the right.
All good here? great! now, why is it a triangle? It is called Triangle because we have three controls at our disposal for making the needle move in either direction.
Before I talk about each of those controls, let's go down the memory lane, all the way to math class. Do you remember the theorem in geometry that says "the sum of all internal angles of a triangle is 180"? There are multiple solutions to this equation, right?. The same happens with the exposure triangle; to capture the right amount of light, there could be multiple solutions but some are more creative than others and you get to choose the one that better expresses your vision for that scene.
The three controls are: shutter speed, aperture, and ISO. Each one has an impact on exposure AND a secondary effect.
#1: SHUTTER SPEED
This refers to how quickly the shutter will open and close to allow light come thru. It is measured in seconds (usual range is from 1/4000" to 30"). With a faster shutter speed, less light is captured and with a slower shutter speed, more light is captured.
The secondary effect is its impact on sharpness. A faster shutter speed freezes your subject while a slower shutter speed will blur the moving subject.
A very fast shutter speed (> 1/500") was priority here to freeze these birds in the air.
In cases where the moving subject must be sharp, shutter speed becomes a priority and the other two controls must be adjusted accordingly to ensure proper exposure.
Finding the proper shutter speed for your subject requires trial and error, I usually start with these values below and check sharpness on preview for any necessary adjustments.
Fast moving subject (i.e. birds flying)
Faster than 1/500"
Slow moving subject (i.e. people walking)
Faster than 1/100"
Non moving subject (i.e. house)
Faster than 1/50" to avoid handshake
A slower shutter speed (< 1/25") is commonly used creatively for capturing water and/or cloud motion. These shots are referred to as "Long exposure", they require a tripod and very possibly a neutral density filter both of which are a topic for another day.
A neat fact: Did you know that a moving object will disappear if the shutter is open long enough? Check this image at Central Park NYC, taken during a cloudy Spring day in 2019, where I experimented using a slow shutter speed (1.6") to blur people.
The most important thing to remember about this number is that it tells you how wide the lens opens to capture the light. Think of your eye, if you squint or open wide.
The format is "f/number" and depending on the lens it usually ranges from f/2.8 (wide opening) to f/32 (narrow opening). When the lens opens wider, more light comes in than when the lens opens narrower. The number is 2 digits, for example: 2.8, 4.0, 7.1, 11, 13, 22
The secondary effect is the impact on depth of field. Hmmm, let's pause here for a moment.
What is "depth of field" (DoF)? This term refers to the distance between the first subject in focus to the last subject still in focus. Let's observe these examples:
Only the lizard is in focus, everything behind or in front is blurry. The DoF is narrow.
In this scene, the man, the waterfall, the mill, all are in focus. The DoF is deep.
To tie back to aperture: a narrow aperture (large f/number) captures less light but gives you a deeper DoF. The wide aperture (small f/ number) captures more light but gives you a narrow DoF.
The acronym ISO stands for International Standard Organization which doesn't really give away its meaning so we just say ISO. It determines the sensor's sensitivity to light. Common range goes from 100 (less sensitivity), 200, 400, 800, up to 6400 (more sensitivity) and even higher in more advanced cameras. As the ISO doubles, so does the amount of light captured.
The secondary effect is that with higher ISO, the photo will also be more grainy. Grainy? how? Basically, the camera will be introducing random speckles in the photo giving it a grainy look, the higher the ISO, the more speckles and when the shutter speed is low, the amount of speckles increases further. This is referred to as noise.
At ISO 2500, this photo of the Northern lights in Iceland is visibly grainy even at this size, imagine on a large print!
My personal preference is to keep ISO as low as possible even if that requires the use of tripod. For low light photography, higher ISO is a necessity though there are several more advanced techniques used to reduce the noise.
Note: some cameras are better at handling noise than others, usually full frame bodies do better than crop-sensor bodies.
And that is the introduction to exposure triangle; the controls and corresponding tradeoffs. If they sound too complicated, fear not! It is just a matter of practice. Wherever you are, keep shooting and try different combinations!
Here are a few more examples, all shot handheld. Hover over/touch the photo to see the settings used and observe the results.
For most landscape images, I use aperture f/8 through f/16 to have more of the scene in focus
While the aim is to have a balanced exposure, you can use the triangle as another tool for your creative process. It is understandable that a night scene will be darker than a day scene just like silhouettes are a very valid composition technique . Understanding exposure allows you to use it intentionally.
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