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Aperture, ISO, & Shutter Speed Tutorial

Have you ever seen a photograph of a waterfall, where the water is smooth as silk? Or how about a photo of a dolphin jumping out of the water where the dolphin itself is sharply focused and not blurred beyond comprehension? You can’t achieve those looks yourself using the camera’s auto mode, unfortunately.

Today I’m going to try to shed some light on the three most important settings in your DSLR camera that control how it actually takes a photo: Aperture, ISO, and shutter speed. These three parameters are related to each other so you need to understand all three to get the whole concept. When you operate your camera in auto mode, it’s primarily these three things that the camera is controlling for you. To progress as a photographer and take better photos, though, you really need to be operating your camera in one of the manual modes. This gives you infinitely more control over the look of your photographs.

ISO Sensitivity

If you remember back 20 years ago when people actually bought film for their point & shoot cameras, you’ll recall that you had to choose the type of film you wanted by ISO number. The most commonly available film 100, 200, or 400 ISO film. You’d use 100 ISO film for a bright, sunny day, 400 or higher for evening and indoor shots with a flash, and 200 for something in between. In other words, the ISO number was chosen based on how much light would be available when shooting your photos.

You’ll be happy to know that it’s exactly the same concept for digital cameras! Except now, instead of buying different types of film, ISO can be changed on the fly at the push of a button.

The same rules apply now for digital cameras. Higher ISO numbers make the camera more sensitive to light, and low ISO numbers are used when there is plenty of light available. But exactly how much light is plenty, and when then, do you need to raise it higher?

The answer is, it depends. Aperture and shutter speed both play a role in determining what ISO is required, and we’ll be looking at them in a minute. A simple rule to follow though is to always keep the ISO as low as possible, only raising it when necessary. An ISO of 100 is typically the lowest that most cameras go, so start there.

That might sound counterintuitive, though. Why wouldn’t you want the camera to be more sensitive to light? Isn’t that the camera’s job to sense light and make a photo? The reason is that higher ISOs introduce something called noise into the photo.

From afar, noise looks like a sort-of graininess, and up close it’s actually a random pattern of bright or off-color pixels spread across the photograph. In some situations, you may actually be going for a grainy look to your photo, but 99% of the time noise is undesirable and is the reason why high ISOs should be avoided. In modern DSLR cameras, noise starts to be visible at as low as ISO 400 but doesn’t really become a problem until ISO 1600 and higher.


Aperture is just a really complicated word for an opening.

Inside the lens of your camera is a number of movable blades that move to control the amount of light that is permitted through. When we talk about controlling the aperture of the lens, what we’re really interested in is controlling how big the opening is and how much light is let through to the camera itself.

Why do we care about this? Well, it turns out that there’s some physics involved, and one of the consequences of changing the aperture is that you also change the depth of field as well. Depth of field is a term that refers to how much of the image is in focus. Photos with a very shallow depth of field may have only a very specific part of the photo that’s in focus with the rest blurred away. This is

Photos with a very shallow depth of field may have only a very specific part of the photo that’s in focus with the rest blurred away. This is a very effective technique that photographers can use to draw attention to their intended subject.

On the other hand in photos with a very deep depth of field, virtually everything will be in focus. This is common practice in landscape photos, where it may not be a particular part of the photo that the photographer wants to draw attention to, but the entire scene as a whole.

And how is it measured? Aperture is measured in something called f-stops, denoted like this: f/1.4, f/2, f/2.8, f/4, f/5.6 etc. There are a rhyme and reason as to what the number actually represents but it’s beyond the scope of this beginner’s tutorial. All you need to know at this point is that your camera lens has both a minimum and maximum f-stop, and there are a fixed number of steps in between corresponding to different opening sizes.

Just to complicate things, however, big f-stop numbers correspond to a small aperture, and small f-stops mean a large aperture. So for example, an aperture of f/16 is much smaller than an aperture of f/4.

It’s these f-stops that you can choose as a photographer to change your depth of field. The larger your aperture (smaller f-stop), the more shallow your depth of field will be and vice versa for a small aperture.

Shutter Speed

I saved the easiest to understand setting for last: Shutter speed. When your camera actually takes a picture, it opens it’s shutter (think of it as a door), for a specific length of time to allow light to enter and record the photograph. It’s this length of time that we’re interested in controlling when we talk about shutter speed.

For most photographs shutter speed will be just a fraction of a second. Many modern DSLR cameras are able to open and close the shutter in just 1/4000th of a second at the fastest — some cameras even faster than this.

But what are some examples of why we would want to control the shutter speed? There’s really two scenarios:

The first is situations where we want to photograph something that is moving very fast, i.e. sports, a hummingbird’s wings, etc. To capture these sorts of things in a photo without any motion blur, the shutter needs to open and close very fast.

A second case is when you actually introduce motion blur. This is how you achieve those silky waterfalls for example. By keeping the shutter open for a long time (seconds or more) any movement in the frame is blurred and becomes smooth.

Those are the two primary examples of why we would want to control shutter speed directly, but as I’ll show you in the next section, aperture and shutter speed work hand in hand to produce the correct exposure.

How Aperture, ISO, and Shutter Speed work together

As I mentioned at the start, aperture, ISO sensitivity, and shutter speed are all interrelated and work together to produce the photo’s exposure. Exposure is just a fancy word to talk about how bright a photograph is. We’ve all seen underexposed (too dark) and overexposed (washed out) photos before. A properly exposed photo requires the correct combination of aperture and shutter speed for the given ISO that you have chosen.

DSLR cameras typically have three different modes that allow the photographer some form of manual control over these settings:

  1. Aperture priority mode (A-mode on Nikon, and Av mode on Canon cameras): This mode lets the photographer choose the aperture, and the camera automatically chooses what it believes to be the correct shutter speed to produce a proper exposure.
  2. Shutter priority mode (S-mode on Nikon, and Tv mode on Canon cameras): This mode lets the photographer choose the shutter speed, and the camera automatically chooses what it believe to be the correct aperture to produce a proper exposure.
  3. Manual mode (M-mode on both Canon and Nikon cameras): This mode lets the photographer choose both the aperture and shutter speed manually.

As we talked about earlier, the ISO should be kept as low as possible as a starting point, but may need to be adjusted depending on the aperture and/or shutter speed. Let’s look at an example where this might happen:

You are photographing a frog in the evening and it is very dimly lit outside. You want to have the frog in focus and the background blurred so you set your camera to aperture priority mode and select a large aperture (low f-stop number). Your ISO is set to 100 because you want to minimise noise in the photo. The camera looks at the ISO and aperture you’ve selected and calculates a shutter speed of 4 seconds required to properly expose the photo! That isn’t going to work! The frog will move in that period of time resulting in a blurry photo. So you adjust your ISO up to 800 and now the shutter speed is just 1/2 second — much better!

And that, in a nutshell, is how aperture, shutter speed, and ISO are interrelated. The best advice I can give is to go out, pick something to photograph, and to start in aperture priority mode at the largest aperture. Take a photo, then stop down to the next aperture and continue all the way until you reach the camera’s minimum. At the same time, play around with ISO and see how that affects the shutter speed. Have fun!

Was this article a help to you? Is there anything that wasn’t clear or that I’ve missed? Please let me know in the comments!

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