The Exposure Triangle
There are three things that make up a photo’s exposure:
3) Shutter Speed
The proper combination of the three, produces a properly-exposed photograph.
It may seem difficult at first, but understanding how these three components of exposure work is pretty straightforward. The more experience you gain in photography, the easier it’ll get. You’ll find that it’ll become natural to you over time. You’ll take a photo, see what you got, make an adjustment and nail it. You WILL get there.
This is the first point in the exposure triangle.
It’s unimportant what ISO means. It’s an international standard basically. Back in the film days, we’d talk in terms of “ASA”. Again, a standards organization. We’d refer to it as your “film speed”; the film’s sensitivity to light.
These days, we talk about “ISO”.
Your camera has a base ISO. My old Nikon D700’s base ISO is 200, while my Nikon D750 has a base ISO of ISO 100. That’s a full “stop”. If it’s a crazy bright sunny day, being able to go down to ISO 100 comes in handy as it lets in half as much light than at ISO 200.
Many cameras allow you to go lower than that (often called “L 1.0” or similar) and higher (H 1.0, H 2.0, etc.), but it’s generally not recommended to venture into the territory not marked with actual ISO values. On the lower side, it’s said that you lose dynamic range. On the higher end, the digital noise is so bad it’s often unusable, but for photojournalism when getting a noisy shot is better than no shot at all.
How are the ISOs created you may ask? Basically, the camera’s software basically amplifies the base ISO’s signal to get the other ISO settings. Thus, digital noise. Back in the day, we’d talk about “grain” at the higher film speeds. These are not the same thing.
The great news is that as technology progresses, the camera manufacturers are able to give us higher and higher ISOs so we can let it more light and capture those moments we strive to get. And as they do this, the high ISOs which previously were noisy, become cleaner and cleaner. There’s going to come a time where you’ll be able to shoot at a crazy high ISO like 51,200 and it look like ISO 100 does now. Those days are coming.
As represented by the Lens Shark™ logo at right, an aperture is a set of blades inside a lens which, when opened and closed, help control how much light passes through to your camera’s image sensor.
When those blades open as much as they can, we refer to that as “shooting wide open”. An example of this would be shooting at an aperture of f/1.8 on your 50mm f/1.8 lens.
If you were to shoot that same lens at f/22, we would refer to that as “stopping down” your lens and very little light would get through.
Aperture values, measured in “f-stops” or commonly referred to as “stops” correspond to how big or small the aperture is.
Aside from helping to control how much light gets to your sensor, the aperture you choose also helps to determine the depth-of-field (DoF). There are other factors involved when it comes to DoF, but the aperture you choose greatly determines how much in front of and behind your subject is in focus. It can be a tiny sliver or it can be virtually infinite.
The way I’ve always explained to people is like this:
Small number (like f/2) = small amount in focus
Larger number (like f/22) = large amount in focus
To see examples at various apertures, click the graphic below. (Opens new page)
Isolating your subject
If your goal is to isolate your subject so they’re in focus and the background is out-of-focus, you would put your camera in Aperture Priority mode (“A” or “Av” depending on the brand) and dial in the smallest number your lens is capable of. This will open the aperture blades wide and the background will fall away. That background blurriness is called “bokeh”.
When you want everything in focus
Conversely, if you shoot landscapes and want everything from a flower in the foreground to mountains in the distance to be in focus, you’d set your aperture to the biggest number your lens will do (like f/22).
Shooting “wide open” means setting your lens’ opening to the widest it’ll do. This will be on the small number end of the aperture spectrum. So, if you have a 50mm f/1.8 lens, this would be at that f/1.8 setting.
Stopping down your lens is heading in the opposite direction and choosing a bigger aperture number. In doing so, you’re closing the opening in your lens and will have much more in focus. Since you’re limiting the light coming into your lens, you’ll be getting a slower shutter speed as the aperture numbers get larger.
On Nikon cameras, this is the “S“. On a Canon camera it’s “Tv” (old school term meaning “Time Value”).
Film cameras had this and so does your digital camera. It’s a curtain which moves at varying rates of speed vertically past your camera’s image sensor, allowing varying amounts of light to hit it.
With an extremely fast shutter speed such as 1/8000 of a second, the shutter is open so briefly that very little light gets in.
With a much slower shutter speed like 1/60 of a second, the shutter is open quite a bit longer and that, in turn, allows more light to hit your image sensor.
At any given ISO and aperture, 1/8000 of a second will result in a much darker (if not completely black) image than 1/60 of a second would.
In addition to controlling how much light hits your sensor, it also determines if your image is likely to be blurry or not. If you’re photographing your children running around your living room, it’s not a good idea to be shooting at 1/60 of a second as that’s likely to result in a blurry image. While 1/8000 of a second would be overkill in that situation, a faster shutter speed will greatly help. As would a “fast” aperture (such as f/1.8) and a higher ISO (like 3200 ISO) as both will allow in more light and reduce your chance of getting a blurry image.
Putting it into practice
Like anything, the more you do something, the better you should get at it. If you take your time and see what worked and what didm’t, in time you’ll be able to make the necessary adjustments on the fly.
You’ll be faced with a scene before you which you’d like to photograph. You’ll set your camera to Aperture Priority (as the vast majority of pros do) and dial in your maximum aperture (a small number like f/2.8) to 1) let in the most light and 2) blur out the background as that’ll help you produce a sharp photo and isolate your subject. You’ll choose a reasonable aperture to shoot the photo at; one which will not be too noisy, but will still give you the light-gathering power you need. Then you’ll take a photo knowing your camera will pick a corresponding shutter speed for you.
You’ll check the back of your camera and see what you got. Too dark? No problem! You’ll know that having already chosen your maximum aperture and the highest ISO you’re comfortable using that you need to lower your shutter speed. Maybe you accomplish this with Exposure Compensation (the +/- button on your camera) or maybe you switch to Manual model and dial in your settings.
YOU are in the driver’s seat.
Photography doesn’t have to be scary.
Once you know the basics, you can tweak your settings until you get it right. Having the benefit of a large LCD on the back of your camera is a huge learning tool. In the film days, we didn’t have that kind of instant feedback. The learning curve is a lot shorter now.
Take a photo. See what you got. Make an adjustment. Take another photo. Repeat if necessary. It’s that easy.