Understanding the relationship between Shutter Speed, Aperture, and ISO
What is the Exposure Triangle?
Beginning your journey in photography can feel quite intimidating as you browse through the settings of your camera, read through instruction manuals, and watch countless YouTube videos. Where does one actually begin to figure out the meaning of each setting and all those random numbers listed on your camera? Well luckily you're in just the right place! I want to help cover the very basics that will get you on your way in your journey, and that starts with covering the Exposure Triangle! Before looking into anything else on your camera, it's important that aspiring photographers understand what's happening beneath the hood (or should I say lens??) each time you click the shutter and take a photo. I'll cover the three variables shaping each image: Shutter Speed, Aperture, and ISO and explain how you can wield each piece of the triangle to maximize your creative control over the camera.
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Let there be Light!
Have you ever wondered what's actually occurring each time you hit the shutter and take a photo? Although it's tempting to believe that something magical is happening in your camera, there's real science taking place! At its core, a camera is a light recording device, taking each photon that bounces of your surroundings, funneling it through your lens, and measuring it on the sensor within your camera body. Okay, that's all fine and dandy, but as photographers, we don't want to just record light; we want to control it to realize our creative ideas!
That's where the Exposure Triangle comes in! There are three main settings that we control to dictate how light reaches our sensor: Shutter Speed, Aperture, and ISO. Every time a photo is taken, these three settings perform a little tango with each other to create an exposure (does that mean it actually takes three to tango??). Shutter Speed controls the length of time that light make its way to the sensor, Aperture controls the size of the opening in your lens letting light into the camera, and ISO controls how sensitive your camera sensor is to the incoming light. Now it's important to note that whenever you adjust one of the settings, the amount of light reaching your camera sensor will increase or decrease, and therefore you will need to adjust at least one of the other settings to bring the exposure back to balance (unless you want to increase or decrease the exposure level). So for every given photo opportunity, you have an incredibly large amount of possible combinations of Shutter Speed, Aperture, and ISO to use.
Before we get into each setting, let's talk about the concept of "Stops" first. Simply put, a "Stop" is the doubling or halving of your exposure. When we adjust settings on our camera, we are either doubling or halving the amount of light reaching our sensor (though most cameras let you adjust settings in fractional stop increments, like 1/3 of a stop) and this would be referred to as increasing or decreasing your exposure by a "Stop." I'll refer back to this while I explain Shutter Speed, Aperture, and ISO below, so keep this in mind.
Now let's dig into how each setting affects our final photo!
Shutter Speed
Perhaps you want to catch split second action at a sporting event or slow down time and create a silky smooth photo of a waterfall? Shutter Speed should be your first consideration while adjusting your settings to make either of those options happen. Generally speaking, cameras will give you the options to use shutter speeds between 30 seconds long and a miniscule 1/8000 seconds long, with many "stops" between the two (30 sec, 15 sec, 8 sec, …., 1/2000 sec, 1/4000 sec, 1/8000 sec).
I used a slow shutter speed on the left to enhance the flowing water of the waterfall and a fast shutter speed on the right to freeze the action at the baseball game.
There are certain circumstances where this number will be imperative to capturing your artistic vision for a photo. For sports and wildlife photography, or any instance when you want to freeze time, you will want to prioritize a fast shutter speed (I recommend at least 1/250 sec. or shorter for quick scenes). For some landscape, cityscape, or astrophotography applications, you may want to intentionally draw out the shutter speed to the longer end of the spectrum so you can smooth out flowing water, car headlights, or be able to capture the milky way in the night sky.
Photo Tip: If you're hand holding your camera, it's recommended that you always set your shutter speed to at least double your focal length. (ex: 50 mm focal length = 1/100 sec shutter speed)
Keep in mind that as you adjust your Shutter Speed, your camera will adjust Aperture or ISO to balance the exposure (unless you're in Manual mode). This can lead to changes in your depth of field and overall sharpness, as you will read about in the next two sections.
Aperture
Have you ever wanted to achieve that artistic blur (bokeh) in the foreground and background of your portrait photo? Or maybe you want every part of the grand landscape in front of you to be in perfect focus? Adjusting your Aperture will be your main focus to achieve those results! The aperture setting adjusts the size of the opening in your lens that lets light in and is noted on your camera by an "f-stop" (f-stops typically range from f/1.4, f/2, f/2.8, ...., f/16, f/18, f/22). The smaller f-stop numbers actually correspond with a larger opening size while the larger numbers correspond with a smaller opening. To make this even more confusing, as you may have noticed, the f-stop numbers don't exactly double from one stop to the next like shutter speed does. To get a little math-y, the f-stop numbers actually refer to the ratio between the focal length of your lens and the diameter of the opening in your lens. For example, at f/2 and a 50 mm focal length, the diameter of the lens opening would be 25 mm. While the f-stop numbers don't double/halve with each stop, the area of the opening is doubling/halving with each stop. This means that from f/1.4 to f/2, you are halving the area of the opening in your lens and therefore decreasing your exposure by one stop.
A wide aperture can be used to create separation between the subject and the background like in this example of a Brown Headed Nut-hatch.
A narrow aperture can be used to achieve sharp focus from foreground to background like in this example from Delicate Arch.
The aperture setting you choose significantly impacts the Depth of Field of your photo. Depth of Field determines how much of a scene is captured in focus. Large apertures let more light into the camera but decrease the depth of field while small apertures take in less light but increase the depth of field in your photo. For this reason, as a landscape photographer, aperture is my primary focus when I setup a shot because I want the entire scene to have crisp detail and a small to medium aperture will help me achieve this (I try to keep my aperture at f/8 or smaller for landscapes). This isn't a hard and fast rule though, as certain scenes will require you to balance your aperture with other settings to get the photo you desire. For example, I need to use as wide of an aperture as possible when capturing the Milky Way because there just isn't enough available light when the sky is so dark! And for portrait photography, or any case when you want to isolate the subject, using a wide aperture will provide a narrow depth of field to blur out the foreground and background.
Photo Tip: If you want to achieve sharp focus, but are worried that your small aperture will decrease your shutter speed too much, mount your camera to a tripod so it will remain steady at slower shutter speeds.
Now that we've covered Shutter Speed and Aperture, you can start to see how adjusting one setting will have an effect on the other. For example, setting a small aperture to capture crisp detail will likely increase the duration of your shutter speed, introducing motion blur into your photo. It's important to understand what your primary goal is for the photo, choosing one of these two settings to set first, and then working backwards from there. But even then, you might run into issues creating the exposure you want. So we have one more corner of the Exposure Triangle we can lean back on when all else fails!
ISO
While Shutter Speed and Aperture are physical characteristics of your camera that can be easily measured and observed, ISO is a bit more difficult to pin down for beginners. When I increase or decrease my ISO, I might notice that my photos are getting brighter or darker, but what's actually happening? Back in the film camera days, ISO was determined by the type of film used in your camera, as different types of film had varying levels of sensitivity to light. But nowadays, ISO changes the sensitivity of the camera sensor to incoming light, artificially brightening the image as you increase ISO. ISO settings typically range from 100 to 25600 and potentially even higher in some newer cameras (ISO is listed as 100, 200, 400,... , 6400, 12800, 25600). Each "stop" of ISO is double or half the previous ISO number, similar to how shutter speed works.
You might be thinking to yourself, "Great! I can just use ISO to increase my exposure without a problem!" And to a certain degree you can do that, however; increasing ISO introduces its own unique issues, chief among them is noise. Noise is the random variation of brightness or color in your image and can be caused by high ISO, very long shutter speeds, and camera heat. Noise can quickly deteriorate the quality of your image if you use too high of an ISO setting.
Above are three cropped images I took using different ISO settings. If you click on each image, you can see how increasing ISO introduces more noise into the photo.
Just like Shutter Speed and Aperture, it's important to think about what increasing the ISO will do to your image and whether you should think about adjusting your other variables before moving the ISO too high. I like to keep my ISO at 100 until I've checked my other settings and determined that increasing my ISO is necessary to achieve my goal for the image.
Photo Tip: Although many cameras allow you to use ISO values of 25600 and beyond, I typically never go past ISO 1600 to keep my image quality sharp.
But before you completely write off high ISOs, some types of photography require it. High ISO values are necessary when trying to capture the night sky in Astrophotography. Also, with today's advancements in noise reducing software (such as Lightroom's denoise button) it's easier than ever to get rid of much of the noise in your photo. Just don't go too crazy with it as these programs can diminish the quality of your photo if you ramp them up too much.
Camera Shooting Modes
I want to quickly cover the shooting modes in your camera so you can start applying what you learned above. Your camera will come with many modes that you can select from to take a photo. This will probably be on a dial on top of your camera, and it will give you the options to shoot in Shutter Speed Priority, Aperture Priority, Manual, and likely some other model specific modes (I'd refer to your camera manual for any of the other model specific modes). Each of these modes gives you control over different parts of the Exposure Triangle as follows:
Shutter Speed Priority: You set the shutter speed, Camera adjusts the aperture.
Aperture Priority: You set the aperture, Camera adjusts the shutter speed.
Manual: You set the shutter speed and aperture, and you determine if the exposure is balanced.
For all of these modes, ISO is independent and can be adjusted by you. The camera will then readjust any of the settings that it's in charge of for that particular mode.
Well that's all for today, thanks for stopping by and learning about the Exposure Triangle! I hope this knowledge is useful and helps you out the next time you whip out your camera to shoot! If this is your first time around, thanks for joining! You can stay in touch by subscribing here and I'll keep you updated with new blog posts and other photography updates I have. Until next time!
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