This is the first in a series of four articles about exposure by Andrew S Gibson – author of Understanding Exposure: Perfect Exposure on your EOS camera.

The mode dial on the EOS 60D, showing all the camera's exposure modes

A feature of modern digital SLRs is that most models have several fully automatic exposure modes (the exceptions are some semi-professional and professional models).

If you’re completely new to photography then this is where you’ll start. Fully automatic modes are designed for you to start using an SLR camera without any technical knowledge whatsoever. Just put it in full auto, and let the camera take care of the rest. It will calculate the three settings that make up an exposure ? aperture, shutter speed and ISO ? for you.

If you’ve moved up from a compact camera, then this is probably the way that you’re used to working anyway, as most compacts don’t let you set the aperture, shutter speed and ISO settings individually.

The SLR difference

There are two main reasons for buying an SLR camera. One is to use interchangeable lenses. The other is to give you full control over the camera settings.

Over the last few years, a new class of mirrorless cameras also gives you the same advantages.

By learning to set the aperture, shutter speed and ISO yourself, and understanding the effect that each of these has on your photos, you are getting involved in the creative side of photography.

This is exciting because this process is how you start making photos, not just taking them.

More automatic exposure modes

As well as fully automatic, your camera probably has some more specific fully automatic modes, such as landscape, portrait or sports. These are also fairly straightforward and mean that the camera will try and select settings that suit those subjects, rather than use the generic, one size fits all, settings of fully automatic.

For example, if you choose landscape mode, the camera will set a small aperture as that increases the depth-of-field. The assumption here is that you want everything in the frame to be in focus.

Alternatively, if you choose sports mode, the camera will set a fast shutter speed, working on the basis that you want to freeze the action.

This sounds useful, but I think that these fully automatic modes do more harm than good. They clutter up the mode dial, offer too many choices and can be quite confusing.

But that’s not all. Each of these modes is very restrictive. For example, on my EOS cameras, I can’t adjust the ISO in any of the fully automatic modes. I can’t apply exposure compensation if the camera is getting the exposure wrong. I can’t change the Picture Style, or even decide whether or not to use the built-in flash. The camera makes all these decisions for me, and I don’t get a say. As a creative photographer I don’t like that (no-one likes getting told what to do, right?)

Program, Aperture Priority, Shutter Priority & Manual modes

So how do you address this? The easiest, and best way, is to stick to using the following exposure modes: program auto exposure, aperture priority, shutter priority and manual.

This is the sort of photo you can take with program mode. The precise aperture and shutter speed aren't important.

Program Auto Exposure mode

Program AE is a useful mode. It’s just like using your camera in fully automatic except that it gives you the ability to override the camera’s decisions. Additionally, most cameras have an ‘exposure shift’ function that lets you change the exposure settings the camera selected if you don’t like them.

For example, if your camera has set f8 at 1/250 second (at ISO 200) and you want a larger aperture, you can use exposure shift to change the settings to f4 at 1/1000 second. The exposure is the same but the effect is different.

I don’t use program much myself, but it’s very useful and shouldn’t be overlooked.

Manual mode

I use manual mode quite a lot ? it’s so useful that I’m going to write a separate article about it. Look out for that in the coming weeks.

Aperture priority

In aperture priority mode, you select the aperture and your camera sets the shutter speed according to the ISO. You can control the shutter speed indirectly by changing the ISO.

I use aperture priority for the following subjects:

I used an aperture of f22 to ensure that every part of this photo was in focus, from the rocks in the foreground to the cliffs in the distance.


Depth-of-field is very important in landscape photography. Usually you will want the entire contents of the frame to be in focus, and the best way to do this is to set a small aperture (such as f16), a low ISO (for high image quality). If this results in a shutter speed that is too low to hand-hold the camera without camera shake, I either raise the ISO (to get a faster shutter speed) or use a tripod.

There are a couple of reasons why you would want to use aperture priority instead of landscape mode:

You can apply exposure compensation if the camera gets the exposure wrong.

You can use the hyperfocal distance focusing technique to maximise depth-of-field. This involves switching your lens to manual focus mode and focusing on the point in the landscape that maximises depth-of-field. There’s a good article about this technique here.

You can use a wide aperture to create landscapes with very narrow depth-of-field. Sound bizarre? There are photographers creating interesting work with this technique. Aleksandr Matveev is one of them, and you can see a good example here.

I used an aperture of f2 and focused on my subject's eyes to create a portrait with a blurred background.

I also use aperture priority for taking portraits. This is a favourite technique of mine with prime lenses (which have a wider maximum aperture than zooms). I set an aperture somewhere between f1.8 and f2.8, focus on my subject’s eyes and let the rest of the portrait fall out of focus. The advantage of using aperture priority is that I can look at the results on the camera’s LCD screen, and adjust the aperture accordingly if there is too much, or too little, depth-of-field.

I took this close-up photo of a flower with an 85mm lens. I set a shutter speed of 1/250 second to ensure that the image would be sharp. I often raise the shutter speed when shooting close-ups as any movement caused by camera shake as magnified.

Shutter priority

In shutter priority mode, you select the shutter speed and your camera sets the aperture according to the ISO. You can control the aperture indirectly by changing the ISO.

I use shutter priority a lot when I’m hand-holding the camera. It lets me set a shutter speed fast enough to prevent camera shake, and I if I need more depth-of-field I simply increase the ISO.

Shutter priority also comes in useful when you want to blur motion. I set the camera on a tripod and took some photos at 1/6 second in Jing’An Temple, Shanghai to illustrate this technique. One girl stayed still during the exposure, and the other moved, creating an interesting effect.

Another example where I use shutter priority is when I deliberately move the camera during an exposure to create a sense of movement and blur. The photo below is an example of this technique. Chris Friel is a photographer who uses this technique very well.

Creative Exercises

Now it’s time for some creative exercises and to put these tips into practise:

Aperture priority

Choose a lens, put your camera into aperture priority mode and set the widest aperture on the lens. Take some photos at this setting. The subject can be anything you like, but portraits and close-ups are a good place to start. What happens to the background as you get closer to your subject? What happens if you move your subject away from the background?

I used a shutter speed of 1/2 second to blur the water in this photo of a waterfall.

Shutter priority

Now try a similar exercise in shutter priority mode. Again, it depends on your subject, but there’s two ways to go.

One is to set a fast shutter speed and use it to freeze action. Check out Olivia Bell’s 100 Jump Photographs series ? this is an easy idea to replicate yourself.

The other is to use a slow shutter speed to turn anything that’s moving into a blur. I like to do this with long exposure photos of the waterfalls, such as the one above. You need to put the camera on a tripod to take photos like this without camera shake.

You can try these techniques out over a period of time. The aim is to get used to using the aperture and shutter priority modes on your camera, and taking creative control by selecting the aperture or shutter speed setting yourself.

Andrew S Gibson is a writer and photographer. He’s the Technical Editor of EOS magazine and writes for Craft & Vision. The techniques in this article are explored in more detail in his ebook Understanding Exposure: Perfect Exposure on your EOS camera.

Post originally from: Digital Photography Tips.

Check out our more Photography Tips at Photography Tips for Beginners, Portrait Photography Tips and Wedding Photography Tips.

Aperture Priority and Shutter Priority: Exposure Lesson #1