Technology Explained, Practice
Daniela Bowker
Resolution and pixels and image quality! Oh my! ...

When you hear the term 'high-res' thrown about with such abandon when it comes to images for web use, have you ever stopped to think just how big or how high quality and image meant for the web needs to be?

Resolution and pixels and image quality! Oh my! Saving images for the web
Feature Articles, Photography Theory
Haje Jan Kamps
Low-contrast photographs don't have to be boring

There's an assumption that high-contrast images are more dynamic, more compelling, more inviting. Have a go at some low-contrast photography. You might surprise yourself with the results.

Low-contrast photographs don't have to be boring
Feature Articles, Theory
Daniela Bowker
Seeking balance in your photos

Balance doesn't mean symmetry; it means an internal consistency and tension within your photos. And it's a vital element of composition. 

Seeking balance in your photos
Feature Articles, Photography Theory
Haje Jan Kamps
Training your photographic luck

Great photos might be down to a little bit of luck, but most of that 'luck' you make yourself. Don't believe us? Read on...

Training your photographic luck
Feature Articles, Practice
Daniela Bowker
The ups and downs and ins and outs of ...

Photographing buildings doesn't have to mean wide-angle lenses and fretting about correcting for the keystone effect. Any lens, and angle. Don't believe us? Let us show you!

The ups and downs and ins and outs of photographing buildings

aesthetic effects

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What is exposure?

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The next stop in our (mostly) alphabetical journey through photography's fundamental principles is at 'e', for 'exposure'. Are you ready? Excellent! Onwards!

Exposure

Without an exposure, we wouldn't have an image (that's how fundamental this principle is) because it's the action of revealing your sensor, or your film if you're old-school, to light in order to record an image. Introducing too much light to your sensor will result in over-exposure and a too-bright image. Conversely, under-exposure is the result of not exposing the sensor to enough light, rendering a too-dark image.

Under-exposed to the left; over-exposed to the right; just right in the middle. (Image by Haje)

So far, so simple.

ExposureTriangle

Exposure is measured in 'stops' and controlled by three variables in your camera: aperture, shutter speed, and ISO. As well as determining how light or dark your images will be, they all have other aesthetic effects on your images, which is why you need to understand and be able to manipulate them to produce the images that you want. We started this series with aperture, which controls depth of field. We'll get to shutter speed and ISO and their respective abilities to freeze or blur motion and to introduce noise into our pictures. But for now, we'll concentrate on the impact of varying aperture, shutter speed, and ISO on exposure.

Equivalent Exposures

By giving and taking from aperture, shutter speed, and ISO, you can keep your relative exposure the same, but change how your image looks.

You might've set up shot to get a 'good' exposure, but you decide that you want a greater depth of field so need to use a smaller aperture. A smaller aperture allows less light to hit the sensor, so if you change only the aperture, your photo would be under-exposed. How can we solve this? You can use the other two adjustments to compensate for the lack of light captured by using a smaller aperture: maybe you want to use a slower shutter speed, to expose the sensor for longer? Or perhaps increase the ISO to make the sensor more sensitive? You could even do a bit of both.

Equivalent exposures

Let's look at an example with some numbers. We’ll start with an exposure of 1/200 second, ƒ/8.0, and ISO 400. What would happen if you were to change your shutter speed to 1/100 second? That would let twice the amount of light into your camera compared with 1/200 second, because the shutter was open for twice as long. Your photo will now be brighter.

Now you change your ISO to 200. This halves the sensitivity of the sensor, and the photo will come out looking like it is the same overall exposure. The photo won’t be identical, but from the point of view of brightness, it will be about the same. It’s possible to change any of the settings to compensate for any of the other settings.

A faster shutter speed can make up for a larger aperture, a lower ISO can make up for a slower shutter speed, and a smaller aperture can make up for a higher ISO. They’re all related.

TL;DR

  • 'An exposure' is the action of revealing your sensor (or film) to light to create an image
  • Too much light results in an over-exposed, too bright image; too little light produces an under-exposed, too dark image
  • Exposure is controlled by three variables: aperture, shutter speed, and ISO
  • Exposure is measured in 'stops'

Dynamic Range << Photography Fundamentals >> Focal length