The first thing I tell students that come to my studio to undertake one of my photography tutorials is to take their camera off automatic and put it on manual.
This means that you can still use the cameras light metering system to tell you what exposure is needed, but instead of it choosing the shutter speed, aperture and ISO settings, you will have to manually dial these in. What this forces you to do is move the dials and take more notice of what each shots settings are.
Knowing about camera calibration
What is important to know, is how the cameras internal exposure metering system works. I am not going to go into too much depth about the technical side here, but instead I want to make this explanation as simple as possible to follow. The camera is calibrated by the manufacturers in such a way that it will give the correct exposure in most situations most of the time. To do this it is calibrated to midtone reflections of light. Which means that things that are midway been the extremes of light//white or dark/black, which make up most of the world we see. Grass, tree leaves and bark, pavement stones, bricks, stone, most of the things around us are somewhere on the midtone range. Snow is on the light/bright side and dark shadow is on the dark end. The camera meter looks out of the lens to whatever you have it pointed at in that moment, it evaluates all of the scenery (assuming you have it on matrix metering setting) gives each piece of that scenery a light value and works out what will be the correct exposure.
The scale at the bottom of your viewfinder tells you where on the exposure scale you are with your current cameras shutter, aperture and ISO settings (check out exposure triangle for more about these). -2 on the scale means you are at least 2 stops underexposed, and +2 means you are 2 stops overexposed. By manually moving the shutter or aperture dial one way or the other you will see the marker on the scale move towards the center. When the marker is in the middle of the scale it is at the correct exposure.
so for illustration purposes we compose the shot we want to take and see that the display indicates two stops overexposed. which means there is too much light using the current camera settings, so we move the aperture from f2.8, to f4 (which is one stop different see aperture for more about stops)
At f4 we are still one stop overexposed, so we move it to f5.6 (below) Now the marker is in the middle, indicating that we have the correct exposure.
Taking the shot would provide a perfectly good exposure at this point (providing there is no back lighting,the sky in the shot could provide a slight misreading of the exposure, zooming into the flower only and cutting out the sky, then taking the meter reading may help this, before re-composing the shot and taking.
If we then move the aperture to f8, we see that the marker has moved to the left my one stop, meaning that the shot is now underexposed and needs more light for the correct exposure.
Finally moving onto f11 shows us we are now 2 stops underexposed.
If you take the photography at f5.6 (using the illustrations above) you will get a well exposed image. If you then shift the camera and point the lens to something else, check the scale to see if the marker is still in the middle, if it isn’t then dial the shutter or aperture in one direction or the other until the marker moves to the center, take the shot and you should have a perfectly good exposure.
Photographing in extreme lighting conditions
Now you are using the meter on your camera to give you an exposure reading, based on the average scene, and as we said before this will work in most cases. However if you are photographing a particularly bright/light scenes, such as a snowy scene than you will have to make a slight adjustment. Taking the photography of a snowy scene may fool your camera meter, which thinks the scene should be mid tone, not as white as it is.
Taking the photograph with the marker in the middle will provide an off-white greyish look to the scene, which is because the camera has been fooled into underexposing the shot. If you dial the marker so that it is showing +1 on the scale this will over-ride the incorrect underexposed reading of the built in camera meter. The opposite is necessary when pointing to a particularly black or dark scene.
Back-lit scenes provide a similar problem for the camera meter. Imagine If you are photographing someone on a sunny beach with blue sea and sky in the background and the person you are photographing is facing towards you and away from the sun, so that they are stood in their own shadow. When you set your exposure and move the marker to the middle of the scale, you will have a perfectly exposed image for the sky and the scene as a whole but the persons face will be very dark, because their face will be in shadow.
Again your camera has taken all the data from the scene and worked out the best exposure for the scene as a whole, it doesn’t know that you want a particular part of that scene (ie the person), who is not in the same illumination as the rest of the scene exposed correctly. So you have two choices, either turn the subject so that the sun is shining on their face and retake, or zoom into the subject with your camera so that they fill the viewfinder, excluding any background illumination. Get the marker into the center of the scale. Zoom back out and retake the shot (don’t readjust the exposure again though). This will mean you have metered on the person and the light level that is on them only. This will result in them being perfectly exposed but the rest of the scene will be overexposed. It is your choice as the photographer what you want from the shot and which way is best for your purposes. Actually there is a third option, which is use your cameras built in flash. Meter for the scene as a whole and use your flash to fill in the subject. This is the best option, providing the subject is not too far away from the camera when you take the shot, otherwise the flash will not have the power to illuminate the subject over a larger distance.
- White scene = +1 or even +2 overexpose
- Black or dark scene = -1 or even -2 underexpose
Something to bear in mind when you are dialing in the shutter or aperture to get the marker into the middle of the scale on your camera is to think about the speed of your shutter, if it is under 1/60 you will need to use a tripod to steady the shot. Otherwise you will get some camera shake. Alternatively you can open the aperture more so that you can speed up the shutter, allowing you to hand hold. Faster than 1/60th second will allow you to handhold the camera without camera shake.