Clearly, compromises had to be made when calibrating it. It will have been set up to produce a reasonably exposed image under reasonable outdoor lighting conditions in the hands of a novice photographer because this is how it is most likely to be used unless it is a very expensive model. In this case it is more likely to end up in the hands of a competent user, if only because few folks can spend large sums of money to take family snapshots, so fewer compromises need to be made.
Used with a little thought most cameras will produce good results most of the time, but you need to be aware of the kind of light and exposure conditions that can fool it and how to compensate.
A Classic Case
Let's look at one of the classic cases that cause disapointing results and see if we can persuade the camera to do a little better.
If you take a photograph of someone in a microlight aircraft flying overhead, the chances are fairly high that the resulting image will consist of a nicely exposed sky with a hopelessly under-exposed black blob where the aircraft should be.
Why did this happen?
The exposure metering system inside the camera had no idea that you were interested in what was probably a rather small patch of the area focussed on, so it will have simply averaged the amount of light hitting the ccd element and selected aperture and shutter settings to suit this.
Clearly the underside of the aircraft will have been reflecting much less light than the sky. To compensate you need to overide the camera's own exposure selections and allow much more light through the lens by either opening the aperture wider or leaving the shutter open for longer, or maybe a little of both.
How do we do this?
Most modern cameras will have a whole host of operating modes apart from fully automatic. There will usually be a method of overiding the auto-focus system for instance, as well as a way to switch off most of the auto features to leave the camera in manual mode. There will also be a couple of exposure modes known as 'aperture priority' and 'shutter priority' modes. You will need to refer to the documentation to ensure your particular camera has these features and how to select them.
In order to cope with our microlight aircraft scenario, you will need to be able to select both the aperture and shutter settings without the camera systems interfering. Basically, you will need to have the camera over-expose the scene in order to collect enough light from the subject. Methods of acheiving this vary from camera to camera, so will need to consult your user manual to discover exactly how to do it.
Start by leaving the camera in aperture priority mode. Set the aperture to say, f/8 and view the scene through the viewfinder. If your camera reports it's settings either in the viewfinder or on the back screen, note what it has chosen for the shutter speed. Change your camera to manual mode to allow you to select the shutter speed without changing the f/8 aperture setting and select a shutter speed two stops slower than the camera suggested. This will allow much more light onto the ccd element so the subject will be better exposed than the sky.
To be certain you have a useable image, slow the shutter speed down one more stop and take another shot, then increase the shutter speed to one stop faster than your first selection.
Aim to end up with a number of images taken over at least a three- or four-stop exposure range so you should have a reasonable image in there. If you run out of shutter speeds to play with, close the aperture one stop at a time in stead.
If you are using a digital compact camera it may not allow you to vary the aperture setting. In this case change the ISO value instead as this has a similar effect. This is explained in the article on f-stops here.
Exposure Bracketing
Unless you are an experienced photographer with a good knowledge of the way lighting conditions affect your camera, you will probably have no firm idea about which aperture setting to choose. This is when we use a system known as 'exposure bracketing'. This simply means 'take a lot of photographs at different settings'.
Select a very small aperture and take a photograph. Open the aperture by one stop and take another. Open the aperture by another stop and take yet another photograph. Repeat this until you are in the upper ranges of your aperture choices. Basically the more the merrier, as you are more likely to have a good shot in a larger collection.
This may sound a little hit 'n miss, but there really isn't any option until you gain experience and have a better idea of where to begin your aperture setting. Even then you will need to take a number of shots, but perhaps not quite as many.
The main feature of a digital camera comes to your rescue once again here, because you can instantly preview your work and delete any obvious failures without the cost or the wait of having film developed.
Experiment to gain confidence and experience.
You can duplicate the kind of conditions mentioned above quite easily to see how it all works. Simply stand an object to be photographed on a window ledge and photograph it from indoors. On a reasonably bright day, the amount of light coming in the window from behind the object will be enough to give you something to think about! |
