There are 3 fundamental things to learn about your camera. These three things make up the Exposure Triangle, and if you can get your head around them and their relationships to each other, you’ll be well on your way to understanding your camera and being able to shoot in Manual. So let’s start there shall we. These three elements are ISO, Shutter Speed, and Aperture.
ISO is the unit used to measure how sensitive your camera’s sensor is to light. Every camera has a sensor – this is the part of the camera that when exposed to light reacts and creates an image. You can increase and decrease this sensor’s sensitivity to light in your camera’s menu system.
Example: You’re out shooting some street photography at night, and there isn’t much light around which is going to make it harder to get a proper exposure for your photo or video. So you increase your camera’s ISO so that the sensor in the camera becomes MORE sensitive to light – this means that even with low light, the sensor is now sensitive enough to expose your image properly.
ISO and Grain
It’s important to note that using a high ISO comes at a cost – increasing your ISO will introduce grain into your image. As you increase the sensitivity/ISO, the grainier your image will become. So you need to be careful how much you increase your ISO by, and also understand how much grain it will introduce. Typically, for DSLRs, anything above ISO 800 will start introducing noticeable grain – which is certainly still usable – but from that point on the image quality will degrade noticeably.
Every camera has a shutter – its the mechanism that opens and closes in front of the cameras sensor to control the amount of light makes it through to hit the sensor. Shutter speed is the amount of time the shutter mechanism of the camera stays open.
If you have a fast shutter speed (it opens and closes very quickly), not much light will get in to hit the sensor. If you have a slow shutter speed (it opens and closes slowly), then a lot of light will make it through to the sensor as there’s more time for it to pass through.
What this means is that you can freeze motion or blur motion – and everything in between. As long as you’re maintaining correct exposure levels, a fast shutter speed can freeze a moment perfectly (think sports photography), and a slow one can blur it (think light trail photos). You must make sure that you are still exposing your image correctly, no matter the shutter speed.
It’s worth noting that at low shutter speeds (anything under 1/40 really) it starts getting pretty tough to hand hold and shoot without introducing motion blur into the photos due to micro movements your hand can make, so typically you’d use a tripod or some in-body stabilization + lens stabilization.
ISO and Shutter Speed Example
You’re shooting some event photography in a dark venue, so you need a slow shutter speed to let enough light in to the sensor to expose the image properly – but – humans don’t stay still, at all, so if you shoot with a slow shutter speed, all your photos will be blurred, as your subjects are moving during the time the shutter is open. To fix this, you increase your ISO. This will make the sensor more sensitive to light as we discussed before, meaning you need less light to expose the image properly, which in turn means you can maintain that fast shutter speed you need.
So you see it’s a dance. Find that shutter-speed you’re after and then boost your ISO so that you’re exposing properly at that shutter speed. BUT, remember that too high of an ISO can introduce a lot of grain into the photo – so it’s all about compromise and finding that sweet spot where ISO isn’t too high and your shutter speed is fast enough to freeze/blur motion or achieve whatever look you’re going for.
Or of course, you can change your aperture…on to the third and final piece of the puzzle.
This is the most technical of the three amigos that make up the exposure triangle. It might take a moment to get your head around it, but you’ll get there, and when you do, it’ll all finally make sense (hopefully),
Aperture is the size of the LENS hole that allows light through to hit the sensor. It’s measured in something called f-stops*. Now this may seem confusing at first, but the measurement of Aperture in f-stops actually almost seems the wrong way around, but you’ll get the hang of It I promise. As the aperture increases, f-stop decreases. So a large aperture (or lens hole) that would let a lot of light through the lens to the sensor would actually have a low f-stop number. Equally a small aperture (or lens hole) that wouldn’t let much light through to the sensor would have a high f-stop number.
So, if you have a large aperture, you’d be using a low f-stop like f1.4 allowing max light through the lens. If the aperture is small you’re likely using a high f-stop like f8 or up, which will block a lot of light reaching the sensor.
Depth of Field
Aperture also controls the depth of field (d.o.f) of your picture. Do not underestimate this. The lower your f-stop, the shallower your depth of field.
So for those portrait shots you’ve undoubtedly seen of people where the background is thrown right out of focus with some nice swirly bokeh (the aesthetic quality of the blur produced in the out-of-focus parts of an image), they were likely shot with a wide open aperture and low F-stop so that the subject was the only thing in focus, and everything on a different focus plane is out of focus .
Equally, when you see a big grand landscape photo that’s clear all the way through the image, there’s a good chance is was shot with a higher f-stop as this encourages clarity through all the focus planes of the image. This is because higher f-stops allow higher clarity through your DoF.
Creatively then, deciding on your aperture setting is crucial. Do you want a very shallow depth of field or clarity through your image. They naturally serve very different uses, which i don’t really want to get into, but think of it as a tool to guide the viewers eye. A shallow depth of field might mean only a small portion of your photo is in focus – which will naturally guide the viewers eye to it. There are way more variables that will guide the eye but your depth of field is certainly an important one.
Aperture is another way to control the amount of light hitting the sensor, as well as controlling your depth of field.
Lenses and Aperture Rating
Many lenses have a sweet spot for d.o.f when using higher f-stops which you can test to find yourself, but typically they’re around f8 or f11. Any higher and you can introduce some distortion into the optics of the lens and ultimately the photo – but its certainly not an image killer if you’re up at f22 – its just potentially not offering anymore than f11 would re. clarity through you d.o.f.
It’s important to note that lenses come with a f-stop rating. Often you’ll see a lens described like this 50mm f1.2 or 55-210mm f3.4 – f5.6. The ’50mm’ and ’55-210mm’ indicate the lens focal length. One is a prime lens (fixed focal length, namely the 50mm), and the other is a variable zoom with a variable aperture. the 50mm has a minimum aperture of f1.2 which is low (this could be referred to as a ‘fast lens’), whilst the variable zoom has quite a high minimum aperture of f3.4 which rises as you increase the zoom range. It’s not a fast lens, but it does offer a good focal range.
ISO, Shutter Speed and F-stop together
I hope by now its starting to make more sense in your mind how these 3 parts effect each other. It all comes back to what you’re trying to achieve in your shot, be it photography or video.
It all depends what look you’re going for, what you’re shooting, and where you’re shooting it. Its compromise, but there’s normally a sweet spot in there somewhere which ticks all the boxes, or at least sacrifices a little on all of them to compensate to get the job done.
Here are 3 examples illustrating the issues i just covered. Have a read through and see if you understand the thinking behind them.
1) I’m a sports photographer shooting an American football match. I want to freeze motion so i can catch that iconic moment with absolute clarity, no motion blur, and with a shallow depth of field to blur the background so that all the emphasis is on the players. Unfortunately, the match is during the early evening though, so the light isn’t great. I want to shoot at a high/fast shutter speed so there’s no motion blur, but this means there’s not a lot of time for light to properly expose the sensor. Fortunately, i also want a shallow depth of field so all the focus is on the subject(s) in the image, and my lens offers a minimum aperture at f1.2, so I’ll shoot with that and keep my fast shutter speed. My image might still look a little underexposed, so I’ll increase my ISO until I’m happy with the exposure. If i don’t want to introduce that much grain at a high ISO, then I’ll have to sacrifice a bit on the shutter speed as the aperture is as wide as it can be at f1.2 for my lens.
2) I’m an event photographer shooting a concert at night. I want a shot of the crowd that’s clear all the way through the image (dof) with no motion blur, freezing the moment. The light isn’t great because its dark, and i need a high shutter speed to freeze the moment. I also need a high(ish) f-stop to help make the photo clear all the way through the image which means i can’t get any extra light by lowering the f-stop. This all means that i either compromise on shutter speed, or i ramp up my ISO. I would probably ramp up ISO to my accepted limit i have for my camera and then sacrifice slightly on shutter speed up until the point i know the image is still just about sharp. If there was still an issue, i could lower the f-stop by one level, or push the ISO one step further and just deal with the grain in post-production.
3) I’m a landscape photographer and i want to shoot some mountains with some motion blur in the clouds above. I want the image to be sharp all the way through the depth of field as well. So, i’ll set my camera at f8 for the depth of field, then I’ll set my ISO at its lowest as i can compensate for the lack of light with my shutter speed as i want it to be slow to introduce some motion blur. If i couldn’t lower my shutter speed enough to get the motion blur i wanted without over exposing, i could use an ND filter (a lens attachment that is essentially a pair of sunglasses for your camera) that would make the image darker by a set amount – which i can then compensate for by lowering the shutter speed some more which will in turn introduce more motion blur as well.
*F-stop is strictly actually the ratio of the system’s focal length to the diameter of the entrance pupil, but its easier to just think of it as the measurement of Aperture.