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Photography tips: exposure

TIME : 2016/2/29 11:26:34
(D'Arcy Norman)

Photography tips: exposure

Don’t know your P from your AUTO? Here we explain how to control exposure on your DSLR to improve your travel photos

Many photography buffs dismiss compact cameras as ‘just point and shoot’. However, many who use DSLR cameras leave them in fully automatic mode, so the camera makes all of the exposure decisions for them anyway: point and shoot, just more expensive.

However, making a few changes doesn’t have to be complicated; with a few basic tips you can get a handle on your camera’s exposure settings to achieve better results.

Exposure: the basics

Exposure is the cornerstone of photography. At its simplest it affects how dark or light your picture is. Over-expose and your picture will be too light; under-expose and the image will be too dark.

The exposure is controlled by the aperture size (the hole that lets light into your camera) and the shutter speed (the duration that the hole is open). By varying the way these two elements combine you can change the whole look and feel of your picture.

The depth of field refers to the amount of your photo – in addition to your subject – that is also in focus. A wide aperture gives a very shallow depth of field – you might use this when shooting portraits, to blur the background. A small aperture gives a broad depth of field, ensuring most of the image is in focus: perfect for sweeping landscapes.

Shutter speed controls how movement is rendered in your picture. A long shutter speed of a few seconds will allow moving objects to blur while a fast shutter speed (say 1/500th of a second or less) will freeze the action.

If you change only one of the elements – aperture or shutter speed – then the exposure will change, and your picture will get lighter or darker. If you balance any shutter speed change with an aperture change, you can affect movement or depth of field, but the exposure will stay the same.

Meter modes

Most DSLRs present you with a number of options for controlling your exposure, usually on a wheel (with pictograms denoting the various exposure modes) or buried in menus.

The first thing to remember is that all of these modes essentially do the same thing.

The actual level of exposure that the camera suggests is only affected by the meter type that you select – it is the meter that detects the light levels and decides what the exposure should be. The modes simply vary the balance between aperture and shutter speed that are used to achieve that exposure.

There are two metering modes to consider: a multi-zone (sometimes called matrix or evaluative) meter, which tries to read the whole scene in front of you; and a spot meter, which meters a small portion of the image. (Some cameras have a partial meter mode, which is a bit like a spot meter but not as useful as it can’t be used to measure a small part of the picture.)

If you are using an automatic mode, select the multi-zone meter.

Manual exposure

If you select manual mode you set both aperture and shutter speed, retaining full control over how motion or depth of field is represented. Manual also allows you to set a different exposure value to that suggested by the meter – often much faster than setting exposure compensation with automatic exposure.

If you are only going to slavishly set the values suggested by your camera meter, then you are not really using manual exposure, and would be able to achieve the same thing much more quickly using one of the automatic modes.

If you are trying to predict the exposure before taking a picture, use the spot meter on your camera to get a more precise exposure reading. If you are going to shoot a picture and then retrospectively adjust the exposure before shooting another picture, use the multi-zone mode.

Picture-scene modes

On many entry-level DSLRs you will find a series of picture-scene mode options. These allow customisation of settings for a range of different scenarios, typically including landscape, portrait, close-up, night photography and sunsets.

These can be powerful tools as they help the camera to know what it is photographing, which helps to get more accurate exposures. They also customise other settings such as whether the camera will bias shutter speed or aperture, white balance and even saturation. This can lead to much better results if you are shooting JPEG format, and the out-of-camera results are better if you are shooting RAW, so you have to spend less time processing the images on a computer.

The downside of picture-scene modes is that you have to change them each time you move to a different picture scenario.

Exposure functions explained

Program The camera sets both aperture and shutter speed, though you have some control over the flash, ISO value and white balance

Auto Sometimes referred to as ‘numpty mode’, this essentially makes your camera behave like a fully automatic compact. You have no control over the shutter speed or aperture settings

Picture-scene modes Automatic settings tailored to various scenarios – for example, landscapes, portraits or close-ups

Shutter priority You set the shutter speed, the camera sets the aperture

Aperture Priority You set the aperture, the camera sets the shutter speed

Manual You control all settings

TIP: Exposure compensation

If you get an incorrect exposure when shooting in any of the automatic modes, set an exposure compensation to over-ride it. If the picture is too dark, set a plus value; if it is too light, set a minus value.