Understanding Exposure

Digital cameras can handle some exposure error, but understanding exposure properly can certainly help improve your photography.

Exposure is all about how much light you let into the camera.

Too much, and your photos will be washed out, too little and they’ll be too dark.

It is possible to correct a poorly exposed image using software afterwards.

However, there are a few reasons why you should avoid this. Some of those reasons are listed below:

  • If you’ve overexposed you’ll end up with blown highlights – you can never recover detail in these areas of a photograph.
  • If you’ve underexposed, the same applies as with blown highlights. There’s no data recorded in these areas, and you can never recover any detail.
  • It’s difficult to get good contrast in poorly exposed photos
  • It’s difficult to get good colour saturation in poorly exposed photographs
  • It takes up lots of your time correcting things later on! Better to get it right when you take the photo
  • Light meters in cameras can be fooled by certain lighting conditions.

Consequently, it helps to have an understanding of exposure before you press the shutter!

The information here is aimed at digital SLR owners. This is because if you use a compact digital camera you have limited options when it comes to adjusting exposure.

Compact digital cameras will work out the exposure for you, so you don’t have to!

It’s still worth reading on though, as it might give you a better understanding of how your camera is working, and you never know, one day you might decide to splash out on a digital SLR!

And if all this talk of properly understanding exposure completely puts you off ever getting a digital SLR, don’t worry. You can always set a digital SLR to “auto”, and it will handle the exposure for you; or you can come back to this page and take control of setting exposure for yourself!

Understanding exposure – what affects exposure?

There are only three things that can make a difference to the exposure. And two of those involve how much light comes into the camera.

  • The shutter speed
  • The aperture
  • The “film speed”

Understanding exposure – Shutter speed

In understanding exposure, you need to understand shutter speed. The shutter speed is a measure of how long the shutter stays open. All the time it is open, light can enter the camera and falls on the image sensor.

The longer it stays open, the more light enters. If it’s open for too long, the photo will be overexposed. Not open for long enough and your photo will be too dark.

It’s worth mentioning here that the amount of time we are talking about is usually measured in fractions of seconds. In fact, 1/30th of a second is considered slow! It’s common for a digital SLR to be capable of shutter speeds in excess of 1/4000th of a second!

Click to learn more on how shutter speed affects exposure and how to use the shutter speed for creative effects.

Understanding exposure – Aperture

The Aperture? The what? In understanding exposure you need to know what the aperture is and does.

As with shutter speed, the aperture is also a way of controlling how much light enters the camera.

The aperture is an adjustable hole in the lens. It can open to allow more light in. Or it can close to become just a tiny hole, stopping so much light from entering.

Aperture and shutter speed work together – if you have a slow shutter speed (to let more light in) you have to close the aperture to compensate. And visa versa – if you have a fast shutter speed (letting less light in) you have to open the aperture to allow in more light to compensate.

Click for an explanation of how aperture can be used creatively to control depth of field.

Understanding exposure – “film speed”

Film speed? On a digital photography site? I must be kidding! Well. No. For understanding exposure it helps to know about film speed, or ISO. Let me explain . . .

In the old days we would load film into our cameras. The most common film was called ISO 100. The ISO rating was a measure of how sensitive the film was to light.

ISO 100 was fine for everyday use in good light. But if the light levels dropped, you had to compensate by having a slow shutter speed, and a nice wide aperture.

The problem? Once your aperture was fully open (to let as much light in as possible), and your shutter speed was as slow as you could manage and still hold the camera steady (to avoid blurring the shot), and there still wasn’t enough light . . . You loaded more sensitive film into your camera!

The sensitivity of film doubled from ISO 100 to ISO 200. It then doubled again to ISO 400 . . . and so on. The highest you could go as a consumer was ISO 1600. ISO 6400 was available, but only really sold in the pro shops.

So what’s this got to do with digital photography? Digital SLRs allow you to set the ISO manually. So if it gets dark, you can increase the ISO. The downside is digital noise – a speckling effect on photos.

This speckling occurred in the days of film too. The higher the film speed, the more speckling. Back then we called it film grain, and it can be used to good effect.

Source: Digital Photography Tips