Managing Exposure

Many people's eyes glaze over the moment you mention exposure, aperture and ISO, which is a shame, because it is all very simple really. Its also really important, so please persevere with the next few paragraphs!

When you push the button to take a picture with any camera, light is allowed to fall on the cameras sensor (the digital equivalent of film). The amount of light which hits the film determines how bright the picture will be; this is known as the exposure; quite simply the amount of light getting to the camera's sensor.

Now there are two things which control the exposure:

• The shutter speed
• The aperture of the lens (how big the hole is)

Shutter Speed

Pretty self explanatory for the most part - the faster the shutter speed, the less light is allowed to get through so lower the exposure.

Shutter speed is measured in fractions of a second, e.g. 1/30, 1/60, 1/125 etc.

For Boudoir Photography, shutter speed has two important roles to play:

Preventing Camera Shake

One of the most common causes of ruined photos is camera shake - ie. the camera moved while the shutter was open - and the light smeared itself across the sensor.

The rule of thumb photographers have always used is to keep the shutter speed higher than 1/focal length of the lens: for a 50mm lens your shutter speed shouldn't go below 1/50th of a second, for a 100mm lens it should be at least 1/100th of a second etc.

Correctly Syncing With Flash

Balancing flash and ambient lighting is a more advanced technique that I will cover separately. For now it is enough to know that flash units deliver all of their light almost instantaneously, and you need to ensure that the camera's shutter is open at exactly the right moment. Each camera has a flash sync speed, at which it is sure to be able to work. For most cameras this is 1/125th of a second, though more expensive DSLRs will go up to 1/250th.

Failure to get the shutter speed set correctly will result in part of the picture being black - as the shutter curtain closes as the flash is firing.

Aperture

The aperture (or hole size) has the opposite effect on exposure as shutter speed; the larger the aperture, the more light gets through and the brighter the image.

F Stops

Spend any length of time around photographers and you will end up talking in 'f stops'.

Think of these as levels of exposure (ie light). If you increase the aperture by 1 stop (e.g from F4 to F2.8) and increase the shutter speed (say from 1/30 to 1/60th of a second) you will have no effect on the exposure; the two changes cancel each other out.

So why would you do it? I hear you ask!

Two reasons:

• If you were using a 50mm lens, 1/30th of second could result in camera shake, where 1/60th would be safe.
• The wider aperture will result in a more shallow depth of field (less of the picture in focus), which will direct the viewer's attention strongly to your focal point, while nicely blurring out the background... but thats a topic in itself!