Understanding Exposure

Aperture and shutter speed.

Even if you forget all the other technical details about your camera, as long as you remember these two you'll still be able to take great pictures. And you're in luck because that's what this week's lesson is about.

As a photographer, you can control how much light gets to your camera's sensor in two ways:

• Increase / Decrease the shutter speed
• Open / Close the aperture on the lens

You might already know this, but the idea is so important that it's worth stating the obvious. If you understand how the shutter speed and aperture work together to give you a huge range of creative options for your photos, I can guarantee you that you photos will be a lot better.

Do digital cameras even need a 'shutter'?

If you've ever had a film camera, the 'click' you heard when you pushed the button is the shutter snapping open and closed in a fraction of a second.

Digital SLR's still have an actual shutter that actually opens and closes, most point-and-shoot digital cameras save space inside the camera by making the sensor turn off and on for a specially determined amount of time (the 'shutter speed'). And although your camera might not have an actual shutter anymore, the 'click' of the shutter opening and closing is so ingrained in our minds that most camera manufacturers have a recorded shutter sound that plays when you push the button just to make you feel like it's still in there.

Shutter speed 101: What you need to know

Most point-and-shoot cameras have a setting that allows you to set the shutter speed. On the Canon digital Elph, you can customize the shutter speed by choosing the 'Tv' setting.

Once you've switched your camera to 'Tv', you'll find that there's a number in the lower part of your LCD screen (almost always a fraction). This number is the shutter speed.

For example, if your camera has  '1/125' in the lower part of the viewfinder, this means that your 'shutter' will be open for 1/125th of a second. In this case, '1/125' is the shutter speed. Every time you push the button to increase or decrease the shutter speed, it will change your camera's exposure by a precise amount.

Slowing the shutter speed (say going from 1/125 to 1/60) will leave the shutter open longer and let more light in, making your photo more bright. In this case, you would literally be doubling the amount of light hitting your sensor (60 is basically half of 125, so the shutter speed is changing by a factor of two).

 If you increase the shutter speed (going from 1/125 to 1/250), the same idea applies but the amount of light reaching your camera's sensor is cut in half because the 1/250 is twice as fast as 1/125.

Aperture 101: What you need to know

Look at the pupil of your eye in the mirror.

If the room is dark the iris of your eye will open to let in more light, making your pupil look dark. If it's really bright, your pupil will contract with the opposite effect.

The 'aperture' of your camera works the same way as the pupil of your eye. Basically the aperture is inside the lens and allows you to increase or decrease the amount of light that gets through the lens and to the camera's sensor.

On the Canon digital Elph, you can customize the aperture by choosing the 'Av' setting.

Once you've set your camera to 'Av', you'll see another number appear along the bottom of your LCD viewfinder, maybe 3.2, 4, 5, etc. This is the aperture value or 'F-stop'.

As you lower the number, you are actually increasing the opening inside your lens and letting more light hit your camera's sensor. Increasing the number will make the opening smaller, reducing the amount of light that can expose your photo.

Making sense of this: How Shutter Speed and Aperture work together

Now that you understand the basics of shutter speed and aperture on your camera, let's look at how they work together. Once you see how this works, you'll be well on your way to getting pro results from your point-and-shoot.

But first, let me introduce one more concept that relates to light and your camera: 'Stops'.

Photographers measure light in 'stops'. One click on your camera to increase or decrease the shutter speed or aperture is typically one stop. Increase the shutter speed three clicks (say from 1/60 to 1/125) and you've underexposed your photo by one stop if you didn't make any adjustments to the aperture.

The good news is that your camera is designed to automatically adjust your aperture if you change the shutter speed and vice versa.

The important thing is that you understand that the shutter speed and aperture are set up to balance each other. If you open up the aperture to let in more light (say from F8 to F4), you must make your shutter speed faster so that less light is allowed to hit the sensor.

As you experiment with your camera, you'll get the hang of how your shutter speed and aperture will balance each other and give you a range of creative options with your camera that will deliver the pro results you're looking for.

What's next?

Now that you've got a handle on the nuts and bolts of aperture and shutter speed, it's time to get creative. In next week's lesson I'll show you some creative ways you can use your camera's shutter speed and aperture to get some professional effects with your point-and-shoot digital camera.

Stay tuned and thanks for joining the class!