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All digital cameras have a built in automatic exposure system, it's in their very nature to calculate things for you. Unlike film cameras, where you had to pay more for automation, with digital cameras, you have to pay more to get away from having the camera do everything for you.

Automatic exposure systems can set the ISO, aperture and shutter speed to suit the available light but photographers usually want to decide some of these things for themselves.

Ironically, you have to buy the most expensive type of camera, the Dslr, in order to get the simple manual controls that you would find on a basic 35mm film camera. But even this type of camera has a fully automatic mode that effectively turns it into a "point and shoot" camera.

For beginners, fully automatic is the best way to go. Find this exposure mode and you can ignore all the other photographic settings you have. It will set them all to auto. There is, however, one setting that will affect your camera's exposure even when you are on fully auto.


Exposure compensation

All but the simplest digital cameras will have an exposure compensation control. On Dslrs and some slr type cameras is easily accessible on the body of the camera. However, on most compacts, it is buried amongst the menus.


The reason why it is so accessible in the more expensive type of camera is because it is so useful, especially for those who want some control over what their camera is doing. However, the reason you might need to use it applies equally no matter what type of camera you use.


What it does is to adjust your camera's actual exposure relative to the one that it's metering system has decided is correct. In practice it's the simplest way of adjusting the exposure on a camera. If you have just taken a photograph that looks too dark, adjust the exposure compensation to the plus side and take the picture again. If the image is too bright, move it towards the minus end.


The exposure compensation setting works in conjunction with the automatic exposure system in your camera. This means that it will have absolutely no effect if you are set on manual exposure. In all other exposure modes, it works as described above.


You may use this to retake an individual picture or if you find that your camera consistently under or overexposes. Adjust the setting slightly one way or the other and use that all the time. One thing you need to find out is when your camera resets this control after you have adjusted it. Your camera may return it to zero after each shot, when it it switched off or never, unless all it's settings are returned to default. This it worth knowing.


Different exposure modes

On the more sophisticated compacts, slrs and Dslrs you will have a choice of exposure modes. Here is a brief explanation of what they do and when you might want to use them.


Fully automatic

This controls everything. Sometimes more than just the exposure. In most cameras it won't even allow you to decide whether to use the flash or not. You can still change the exposure with exposure compensation, but that's it.


Basic program mode

Also called AE program mode, this will release some control of the camera back to you. There are three settings involved in controlling the exposure; ISO, shutter speed and aperture. Fully auto controls all three but program mode allows you to set the ISO number yourself (or leave it on auto). In fact it allows you to adjust any setting in the camera except the shutter speed and aperture.


You can usually alter the shutter or aperture in program mode, but not independently of each other. Program mode locks the two settings together so any change in one is compensated for in the other and the exposure will stay exactly the same. Only exposure compensation will actually make your picture lighter or darker.


Other program or scene modes

Many cameras have some exposure modes that are identified only by picture icons. When you look them up in the manual you find they refer to things like "sport/action", "portrait", "landscape", "night" amongst others. These settings usually work like fully automatic in that they may set more than just the exposure and you may not be able to adjust anything except exposure compensation. They are meant to be self explanatory. When you are taking any of the type of shots described, the appropriate mode will set your camera up perfectly for it.


Semi automatic modes

These are the exposure modes that are most useful to the serious photographer. They allow you full manual control over either the shutter speed or aperture whilst maintaining automatic exposure. There are two of these modes, namely shutter priority and aperture priority. Both of these modes are similar to the basic program mode in that they lock the shutter speed and aperture together and don't affect anything else, But with one vital difference.


In program mode, if you adjust the shutter or aperture before taking the shot, that setting will only apply to that shot. In contrast, if you set an aperture in aperture priority mode, that setting will remain until you change it or come out of that mode. Similarly, when you set a shutter speed in shutter priority mode, only the aperture will change to give you the correct exposure.


In practice

Why are these modes so useful to the serious photographer? Mostly because they are the essence of how you set up a camera for different photographic effects. The fact is that even though a fast shutter speed and wide aperture will give you exactly the same exposure as a slow shutter speed and small aperture (it's known as the law of reciprocity), the photographic effect will be different.


It depends entirely on what type of photograph you want to take as to just what effect you need. Once you know whether you need a specific shutter speed or aperture, you set that using the appropriate mode and let the camera set the other.


Fully manual

For the experiences user only - it will probably say in the manual. In this exposure mode, you're on your own (use the force, Luke). Actually, You're not completely on your own. You never are with a digital camera, there is always a computer ready to help.


In this case it's the fact that your camera's exposure meter will still be working, constantly reminding you of how wrong it thinks that your idea of the correct exposure actually is. You have to learn to ignore this. You only need to use fully manual when you know that the camera will get the exposure wrong. Believe it or not, there are times when it will do this, or at least not take the shot you want.


For example, if you are taking a lot of pictures in the same lighting then the exposure shouldn't change. However, you are likely to find that your camera constantly makes subtle adjustments to the exposure depending on what is in the frame. If you want to present these pictures as a set, you might prefer a consistent exposure throughout. Using fully manual is the only way to do this.


Occasionally, you might want a deliberately wrong exposure. So wrong, in fact that even exposure compensation won't go far enough. Strange as it may seem, it does happen. For example night photography, fireworks and extremely high contrast situations often require exposure settings that your camera will think are just plain wrong.


Also, if you ever find yourself working in a studio you should know that automatic exposure systems are of no use whatsoever in that situation. The reason you use a studio is to have control over every aspect of the photograph. The last thing you want in that situation is your camera compensating for what you are doing.

Camera exposure modes