How to use a DSLR: Understanding Aperture

When I was 17 I decided that I wanted to study photography. I wasn’t enjoying my AS levels and so after that first year I moved straight onto a Photography BTEC and never looked back. I’d already been using a DSLR when I got to college that September, but I didn’t realise just how much I didn’t know, and what I would learn in those first few weeks.

We were thrown right into the deep end – an SLR (that’s a film camera!) and instructions on how to using the developing chemicals. We would have a list of all the apertures in order on the whiteboard, and a list of the shutter speeds too. Each week we would try to reel them off from memory. We had to use the exposure reading that you can just about see through the viewfinder, or (if it didn’t work, because of the old camera) just guess. Pretty soon you figure out the right balance between the aperture and the shutter speed (and the ISO – but that’s best for another post!) and you could get that exposure right. One thing my tutor always said when shooting film was “shoot for the shadows, develop for the highlights“.

After those first few weeks, I knew I was hooked. After a few conversations that I’ve had on twitter, I figured that now would be a great time to share some wisdom. Now I’m not claiming to be a professional or to know everything, but I hope this information will be helpful to you!

How to use a DSLR: Understanding Aperture

How does a DSLR work?

There are three main elements you need to know about: aperture, shutter speed and ISO. The aperture determines the depth of field (i.e. how much is in focus), the shutter speed dictates how long the camera sensor is exposed to light (thus taking the photo) and the ISO determines how sensitive the sensor is to light. As a general rule, the faster the shutter speed, the wider the aperture needs to be, and vice versa. This will change depending on the overall effect and exposure that you want.

So, what is aperture?

In simple terms, an aperture is an opening through which light travels. In college, I remember being told to imagine an eye because it acts in exactly the same way that a camera aperture would. Your cornea is like the front of the lens – the glass. The pupil would be the aperture, and would expand or decrease depending on the amount of light available. If your surroundings are dark, your pupil will increase in size to allow what little light there is to get in. If the area you are taking a photo of is dark, then the aperture needs to be opened.

There is actually a depth of field preview button on a DSLR, and it’s usually the small button next to the one that you use to remove the lens. With your camera turned on, you can press this button and if you look into the lens itself, you will see exactly what the aperture hole looks like when taking the photo. Keep changing the aperture and then pressing the button, and you will see how much the hole changes through each stop – comparing f1.8 to f22 is quite a difference! If you put your camera in manual mode to look at this, you can also look through the viewfinder whilst pressing this button, and you will see how the scene darkens/lightens due to the shutter speed you have set. Understanding aperture will give you that push you need to get the manual ball rolling.

Wide or narrow aperture?

A wide aperture lets a lot of light in, whilst a narrow aperture lets a little light in. Simple, right? Well, the numbers are a little backwards in my opinion. The numbers increase as the hole gets smaller. So a wide aperture would be something like f1.8, whilst a narrow aperture would be f16. Depending on the lens you are using, you may only be able to get as wide as f4.0, but don’t worry, you can still achieve this effect! You don’t need the heavily sought after 50mm f1.8 (though it is a lovely lens…)

Now, more backwards stuff: A wide aperture will narrow the line of focus – giving you a big depth of field. If you’re shooting at f1.8, not a lot will be in focus. If you shoot at f16, you will get your subject in focus, and possibly a lot of the background too. This is where knowing what aperture does definitely comes in handy. Most bloggers want that ‘bokeh’ effect, with the background completely out of focus. To do this, you need a wide aperture as seen below.

How to use a DSLR: Understanding Aperture

You’ll notice that although both shots have the same aperture, the overall effect is different. This is because of the distance between your subject and the background. The further away from the background your subject is, the more out of focus the background will be. On the right, the K is around a metre or so from the fence. On the left, the K is around half a metre away from the fence. That little move makes a big difference in the amount of background blur. The background I’ve chosen is quite busy because it’s easier to see the change in focus, but if you want a nice smooth bokeh effect, you need to look for a simple background too – like my berry photos in this post.

How to use a DSLR: Understanding Aperture

As we can see in the photos below, the smaller your aperture, the more in focus the photos will be. It’s most obvious in the fence right at the back, and you can see that an aperture like f16 or round abouts would be suitable for landscape shots or shots where you want all the detail of the area you’re in captured. If you do want everything in focus, subject placement like on the right hand side works better because you can see that the background on the left is still just a little more out of focus than the right.

Being able to use a small aperture like this will also depend on the available light; you will need a slower shutter speed to make up time for the little light that the small aperture hole allows in. I’ll talk about that in next week’s post.

How to use a DSLR: Understanding Aperture

I think aperture is a good place to start when learning how to use manual on your DSLR. For the most part, aperture is the most important tool because that’s what determines how much focus you get, and that’s what you’ll be thinking about when you take your photos. If you’re not comfortable with using full manual yet, I would definitely recommend playing around with the aperture priority mode (Av in Canon, and I believe just A in Nikon). This is how I started with my camera before I started college, and it allows you to play with depth of field without having to think about anything else. You will notice how the shutter speed reacts to the size of the aperture, and it’ll give you an idea of what settings are needed.

Hope this has proved helpful, and if you’re stuck or think I haven’t explained something enough, please do ask in the comments or on twitter. I’m always happy to help! Likewise, if you think I’ve explained something wrong or know something I haven’t mentioned, I’d like to hear that too! Next Saturday I’ll have a post on shutter speed and exposure for you!