When a young wallaby in beautiful light glances briefly towards your camera you don’t want to wait forever for the shutter to fire. Thankfully, digital SLRs are highly responsive and so they take an exposure almost immediately on pressing the shutter button.

Before you start

First thing I’d do is get one of those UV filters to screw onto the end of your lens. A UV filter doesn’t do much — well, I guess it filters UV — but I personally use them because they offer a little bit of protection for my lenses. If your lens gets bumped, scratched or dirty then you’ll be glad that replaceable filter took the punishment instead of your expensive lens. Of course there’s a limit to how much protection a lens filter can provide, but at least it’s something.

Attaching a UV filter provides a little bit of protection for your lens. You’ll need to make sure the diameter of the filter matches your lens or else it won’t screw on.

Once it’s attached you can leave it on. Your lens cap should clip right over the top of it when the camera’s not in use.

Fully Auto

Yes, there’s that fully-auto setting which turns your SLR into an aim-and-shoot box. I bet the salesman in the shop pointed that feature out to you. In a hurry? Then select Auto, and shoot. You’ll get a lot of good photos just using that setting. But one day you’ll realise you’re missing out on some of the best fun, and best shots too. Because Auto tries to guess what you want, and even the smartest cameras don’t get it right every time.

Multiple focal points

We’ll start here because this bit can cause an enormous amount of frustration right at the beginning with a new SLR. Modern SLRs often use a whole bunch of auto-focus points to help you take better pics. That is, when they’re not making you take worse ones.

If you have all focus points activated and you take a shot of something surrounded by foliage, like this Red-backed Fairy Wren, then you’re almost certain to end up with the wrong parts of the scene in focus

What I should have done: Here I’ve activated only the centre focus point. This time the bird (Red-browed Finch) is in focus and the other stuff is blurred

Here’s an example. See that blurred thing in the picture at right? That’s supposed to be a wren. But the wrong parts of the image are in focus. This can happen a lot when you have all focal points activated. And it makes sense when you think about it — all those focus points are much more likely to latch onto one of those many bits of foliage instead of that one bit of bird.

That’s why one of the first things I do is choose which focus point I’m going to use. I select it and then the camera remembers my choice until I change it again. Now, to select a focus point will probably mean you need to work in something other than fully-Auto mode. Because we’re only learning here, then Aperture Priority mode (AV or A, depending on your brand of camera) should do fine. You can set your Aperture to f/8 for example, and then choose which focus point to use (you might need to check your camera’s manual to find out how to select focus points)

So which focus point do I use? My most common setting is to activate only the centre one. That means the camera will focus on whatever’s in the middle of the frame as I press the shutter button. As you get more comfortable with your camera and composing your shots, you might find situations where some other focus point, a group of them, or all of them is a better option. But the important thing is that you decide, not the camera.

When I took this picture, I locked the focus on the wallaby’s eye and then aimed slightly to the side (re-composed the shot) before taking the shot. It made the photo a little bit more interesting than having the animal in the dead-centre of the image, while still keeping it in focus

There’s another nice feature about selecting which focus point you want — you can focus your shot by aiming your focus point directly over the part of the scene you want to be sharp. Then press your shutter button half-way down until you camera is in focus. Then, keeping your finger on the button, you can then re-compose your shot. The focus is locked in because you’re keeping your finger held down. When you have framed the shot the way you want it then press the shutter button the rest of the way down to take your photo. (Note that this trick won’t work in servo-focus mode because servo-focus is focusing continuously and therefore refuses to lock.)

And now we can start talking about what I think is the core of SLR photography:

Depth of Field, f-stops and shutter speed

Why am I lumping all these things together? Because they’re all connected.

When you understand this bit then the rest of photography, especially the bits which make SLRs such great cameras, will start making a lot more sense.

I’ll start with Depth of Field

Depth of Field is a term photographers use to describe the amount of distance between the closest and farthest objects in focus. So, imagine you want to photograph a landscape and you’d like everything from the shrubs up close to the remotely-distant hills on the horizon, to all be clearly seen. What you are asking for is lots of Depth of Field (DOF).

In this shot of a Darter, the water was creating lots of distracting ripples in the background and I wanted those ripples to disappear. So I blurred them away with a small Depth of Field

The smaller the f-number, the bigger the hole letting in light

And there will be other times when the background will be just too much of a mess and you’d prefer to blur it away, like in the Darter photo at right. Well, your clever new SLR gives you that option too. Some of the better compact digital cameras can do this, but not as well as a digital SLR. The reason is a bit tricky to explain but for now you can be happy to know that it involves the larger sensor used in digital SLRs.

So then, how do you do it?

Easy! To get a small Depth of Field you go to Aperture priority mode (AV or A on your mode dial) and then you choose a small f-stop number.

Now it’s important I go off on a bit of a tangent here so you’ll understand what I just said. A small f-stop number means you are opening up the hole in your lens — the hole letting the light into your camera — into a big opening (see the graphic at right). And a big f-stop number results in a small opening.

Why does the big number equal the small hole and vice versa?

The answer is, because the f-stop number is a fraction. Well, actually if I’m going to be super-accurate here then I will say it’s a ratio: the ratio of focal length to the diameter of aperture hole.

So let’s say you had a 50mm lens and its aperture hole was opened up to 25mm. In that case, your focal length divided by 2 gives you your 25mm aperture diameter. And so there is your f divided by 2, or in camera-speak: f/2. It’s just like with other fractions you’ve seen, where 1/22 of something is a smaller amount than 1/2 of it, and likewise an aperture of f/22 is a smaller aperture hole than at f/2.

And that’s why f-stops are written to look like a fraction with the f and the number separated with a slash sign, as in f/2 or f/4. Some people prefer to leave out that slash symbol when they describe their f-stops but the important thing is that it means the same thing.

At f/2, the aperture hole has twice the diameter of f/4.

So, f/2 would let in twice as much light as f/4, right?

Actually, no! Wrong! f/2 will let in four times as much light as f/4! And it’s easy to see why: You see, the aperture hole at f/2 will have twice the diameter of f/4. And when you double the diameter of a circle you quadruple its area. Which means four times the amount of light!

Okay then, so how do you control Depth of Field?

Here’s what you need to know: a small f-stop number will give you a small Depth of Field. Which means your subject is in focus but other bits can be blurred. That kind of effect can be especially effective (and flattering) when taking portraits, and it also gives a very pleasing effect of matching the way a human eye works.

And of course, the opposite rule applies. A big f-stop number means a big Depth of Field.

Okay, you’ve survived one half of the equation and you’ve survived all of the harder stuff. Now we bring it all together.

It all comes together

We’ll use f/16 as our example here. You chose that big f-number because you wanted to get lots of Depth of Field. Because you’re letting light into your lens through a very small hole, there’s not much light reaching your camera’s sensor. It’s like being in a house with the blinds mostly closed, making everything seem too dark (underexposed). To make up for that, your camera’s going to want to brighten things back up again by giving the exposure more time to capture more photons. And it does that by slowing down the Shutter Speed. Which is why Depth of field, Aperture and Shutter Speed are all connected.

Have a look at the graphic below to see a rough guide to this whole thing.

Photography becomes a balancing act between Depth of Field, Aperture and Shutter Speed, with you, the photographer choosing which aspect to give priority to, according to what you’re photographing at the time and how you think it will look best.

You can see in the pics of the toy dinosaur above just what a difference Depth of Field makes to a shot. So, if your main concern is providing a soft background, then you give priority to your Aperture setting, because that’s where you control Depth of Field. You choose Aperture Value Priority mode (AV or A mode) and select the best f-stop for the amount of Depth of Field you want. Your camera will then look after the exposure for you by choosing an appropriate shutter speed.

But what if that dinosaur was moving quickly? In that case you would be more concerned about motion blur getting into your photo. So you you tell your camera to give priority to Shutter Speed. That means you go to Time Value Priority mode (TV mode, or S mode or whatever your make of camera calls it), then select a Shutter Speed fast enough to freeze the dinosaur’s movement, and your camera will then pick an appropriate Aperture.

So that’s why they call them priority modes

You’ve probably now guessed why your camera calls them priority modes. In Shutter Speed Priority Mode (or Time Value Priority Mode or whatever else they call it) your camera gives priority to your Shutter Speed when it figures out the exposure settings. When I say it gives priority to it, what I mean is that it uses it as a starting point in figuring out how to get the right exposure.

And likewise, in Aperture Priority Mode the camera gives priority to the Aperture (f-stop) you choose, while you give it the flexibility it needs to choose an appropriate Shutter Speed.

When you want to take control of both of those settings yourself then you switch to Manual Mode.

Because the amount of Depth of Field makes such an enormous difference to the appearance of a photo, a lot of photographers I know prefer to keep their camera in Aperture Priority mode all the time. However, with wildlife or sports photography, where your subjects are often moving quickly, then they might prefer to work in Shutter Speed Priority Mode instead.

An easy rule

I think it’s time to throw in one of photography’s rules because you’re ready for it now: Whenever you half the area of your aperture hole you have to double the exposure time. And vice versa.

Is there anything being left out here?

Yes, of course there is.

Sometimes the light just isn’t bright enough for your camera to get a decent exposure, even after doing all the clever stuff I’ve been talking about.

Back in the old film days, we used fast film for low-light situations. The same rules apply with digital.

By increasing your camera’s ISO setting you will increase the sensitivity of your sensor. Which means suddenly your camera is getting enough light again.

I haven’t discussed ISO until now because I figured you had enough to think about, and I won’t say too much more about it right now for the same reason. But here are a few things about ISO which are worth noting:

This photo of a Superb Fairy-wren has been badly degraded by noise.

• By default, your camera will probably be set up to be taking care of its ISO settings automatically.
• Increasing your ISO settings will allow for high shutter speeds, or small apertures, in less light.
• The down side of relying on ISO happens when you push things to their limits. You see, very high ISO settings tend to create more noise in your pictures. By that, I mean that the photos tend to be speckled with incorrectly-tinted pixels, especially in the shadow areas where the poor-light issue is at its worst. Still, you will probably find that you can take your camera’s ISO settings up a bit without any noticeable loss of image quality, and the pros often do exactly that.

All the other rules still apply, with Depth of Field and how it relates to Aperture and Shutter Speed and so on, but just understand for now that higher ISO allows you to do the same things in weaker light.

To learn how to crank up your ISO you might need to glance at your camera’s manual. But I’ll stress again that you should be wary of maxing out your ISO settings, or else you could get some unusable images.

There are lots of variables in photography and I could go on and on about them. For example, a telephoto lens (one with a very long focal length) will blur your background more than a wide angle lens at the same f-stop, and if you’re interested in why that happens then I explain it here. (Don’t worry — it’s not nearly as complicated as what we’ve just learned!) But once again, the same general rules about Depth of Field, Aperture and Shutter Speed will apply.

What next?

So you’ve made it through the basic concepts behind camera exposure. How you apply this is the trick behind using your SLR camera and that is surprisingly straightforward. I want you to be nice and clear about what we’ve already learned. It’s at the heart of knowing when to choose things like Aperture Value Priority (AV) mode or Time Value Priority (TV) mode as you step outside to take your shots.

And the easiest way to make sense of it all and help you remember it, is by talking about some different situations out in the real world in Part 2 of this guide. You’ll see how we’re using this stuff to make decisions which drive your SLR camera towards much better photography.

PART 2

Beginners’ series on digital SLR photography

 

Other photography stuff

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