When to Use Manual Exposure

Digital cameras have a built in computer that can take a light reading then adjust the settings to give you the correct exposure. This auto exposure system is ideal for beginners and those who either don’t know about or are not interested in ISO numbers, shutter speeds and f/Nos. However, if you do understand these terms, or want to learn about them, this fully automatic exposure system is actually a hindrance, because you have no control over what your camera is doing.There are very few situations where the experienced photographer will not want to control these settings themselves and using a manual exposure mode will give them complete control. In manual mode, the auto system is totally switched off and you have to “use the force” to control the camera by yourself. If you set the wrong exposure, you get the wrong exposure.The manual mode is unique in this respect. All the other exposure modes available are automatic. These different modes only allow you to choose what you will let the camera control but, in terms of exposure, it will always have the last word. If you don’t like the result, you can only use exposure compensation to change it.Manual mode is not for the faint hearted. It leaves you completely on your own and it reduces the technological level of your camera to that of the first one ever built. Auto exposure systems only exist because photographers demanded them. The earliest cameras were all fully manual and only experience could help in setting the right exposure. Once the light meter was invented, photographers no longer needed to guess the exposure but they still had to transfer the meter reading manually on to the camera.This was quite a tedious process so, over the years, meters and cameras became more integrated and exposure systems became more automatic. Auto exposure existed before digital cameras even appeared on the market. It is a very useful labour and time saving system so why on earth would anyone in their right mind ever want to switch it off?

There are very good reasons for doing so, but only in particular situations. These are situations where you know exactly what settings you want. This can only be because either you know what the result will be or you have some other means of adjusting the exposure outside of the camera. The first of these situations is probably the most obvious.Working in a studioStudios are designed to give you complete control over the lighting and this includes the exposure. You would set the shutter and aperture to suit the shot you want and adjust the lights for the correct exposure. If you are about to use a studio for the first time, you will save yourself a lot of time and effort by leaving your camera on manual. As you make adjustments to the lighting, the last thing you need is your camera compensating with adjustments of its own.Even lighting – grey cardIf you take an exposure reading off a grey card then you are setting the exposure for the available light and not for the brightness or darkness of your subject. It is similar to manual colour balance (or white balance) in this respect. When you do a white balance, you would use the same setting for all the shots taken in the same lighting. To some extent, this is also true for your grey card exposure setting.No matter what type of reading you take or how you determine the exposure, once you have decided on the settings, you might prefer to dial them in manually so they stay the same for all the shots taken in the same lighting. If you leave the camera on auto, it will make constant small adjustments to the exposure from shot to shot.There are times when you really don’t want this to happen. Imagine if you were shooting in a room that had one or two windows letting in bright daylight. Your auto system would change the exposure quite dramatically depending on how much of the window could be seen in each shot. If there were people in the shot, their faces would be brighter or darker simply depending on your framing.You might prefer to set the exposure for the people and let the windows bleach out. You might also prefer to keep that setting for all the shots. After all, the actual level of the light won’t change no matter which direction you point or how you frame up the shot.Flash photographyHere too, it can be easier to leave your camera on manual. Unless you are doing fill-in flash, the shutter speed hardly affects the exposure because it’s unlikely to be faster than the flash anyway. On Dslr cameras, it needs to be slower than the sync speed, so you may as well set it there and forget it. The aperture doesn’t affect exposure either. All it controls is depth of field and the range of your flash. Using a wide aperture allows you to take flash pictures at greater distances.The flash itself controls the exposure, it takes a light reading either through the camera (TTL) or through its own light sensor. The reading is made as the picture is taken and the flash is cut off as soon as the correct exposure is reached. Working manually, you would set a speed of 1/60 – 1/125 or thereabouts and an aperture to suit the maximum distance you wanted the flash to cover. Even though your camera is set to manual, the flashgun is still controlling the exposure.Using flash with auto exposure can lead to problems. The camera might try to set the exposure as though you weren’t using flash, which may lead to a shutter speed that is actually too slow to avoid camera shake. Most of the time this won’t be a problem because the flash is fast enough to freeze the action and the camera shake.

Sometimes however, you will get a strange double image. This is because there is actually enough light to have taken a picture without flash at the settings your camera has chosen. What you end up with are two images superimposed on top of one another. Even if there is not enough light for that effect, if there is anything in your shot that is very bright (like a light or its reflection – known as a specular highlight), that can show the effects of camera shake, even though the rest of the picture doesn’t. In those situations, working manually is actually easier.You are not aloneSetting the exposure manually doesn’t mean that you have to just take a guess at it or even use a light meter. There is still one built in to your camera and you may as well use it. In working manually, you would start by taking a test shot with auto exposure on. From this, you can easily work out what settings to use. The point of using manual is to stop the camera changing those settings between shots. If the lighting changed or you moved to another location, then you would take another test shot and work from there.Once you have decided on the settings to use, make a note of them, switch the camera over to manual then dial them in. It makes no difference whatsoever to the quality of your pictures whether the shutter speed and aperture were set automatically by your camera or manually by your own fair hand.