The purpose of a camera is to control how light strikes the film. Control is exercised in two ways: duration and intensity. The quantity of time that light is allowed to shine on the film is controlled by the shutter speed. The intensity of the light is regulated in the lens by an aperture or diaphragm. These are the only two controls which we have.
Film does not work like our eyes. The effect of light shining on film is cumulative. The longer that a piece of film looks at a scene, the brighter that scene becomes. Therefore, to achieve a proper exposure we can either allow a lot of light to strike the film in a very short time, or we can permit just a little light to strike the film but let it build up over a longer time. Both approaches are equally valid. Which method you choose will be governed by your subject and conditions.
If you are photographing a very dim scene, you may have to allow both the maximum amount of light to reach the film, and do so over a long period of time. Similarly, for very bright scenes you may diminish the intensity of the light and still use a very fast shutter speed.
Earlier we mentioned that the intensity of light is regulated by an aperture. Let's look at one more closely. A common aperture is nothing more than a mechanical device with an opening in the middle that can be adjusted to various diameters. Larger openings allow more light to pass through the lense. Although the opening is continuously variable, certain sizes have specific numeric values. These values are called the F-number of a lense.
The largest opening has the smallest number. Thus, a setting of F-2.8 allows more light to pass than a setting of F-8. Lenses are rated by their largest possible aperture. So you may hear people debating the merits of an F-1.7 lens against an F-1.2 lense. The difference is that a photographer could make photographs of a more dimly illuminated scene with the lense having the smallest number. When a photographer speaks about how fast a lense is, he is talking about the largest aperture that it can attain.
Depth-of-field is a technical term describing how much, in depth, of your photograph is in focus. Some examples will do much to convey this optical property. Interestingly, the depth-of-field is controlled by the aperture. The smallest aperture (the highest F-number) provides the greatest depth-of-field. However, before you vow to always use the smallest aperture, remember that a small aperture requires you to use a longer shutter speed. Thus, if you are going to photograph a chair and you want it all in focus, go ahead and set your aperture to its highest F-number, place your camera on a tripod, and make the photograph. But if you wish to photograph a vollyball game, you will have to compromise in order to freeze the action of the players.
When using a shutter speed of less than 1/30 second you should use a tripod. Even if you are very steady, your heartbeat will cause a blur by 1/4 second. To freeze normal human motions, use 1/60 or 1/125 second. For sports use 1/250 or 1/500. 1/1000 second is rarely required. 1/2000 is rather ridiculous.
|A fast shutter speed.||A slow shutter.|
From a mechanical perspective, this is what photography is all about. The aperture determines how much light passes through the lense and the shutter determines how long that light shines on the film.
The decisions about shutter speed and aperture ought to be made by the photographer. No camera, no matter how much it cost, can always make the correct decision for you. The fancy automatic cameras can set set themselves to make an exposure that is the correct brightness, but they can never decide when they need to use a quick shutter speed and sacrifice some depth-of-field. Only you can do this. Photographs are made by people, not cameras.
To chose the correct aperture and shutter speed we must first measure the intensity of the light we wish to record. If you are exceptionally skilled, you may be able to look at a scene and know; if you are human, you will use some sort of light meter. Most cameras have a built-in light meter. This discussion will help you understand how it works. If you have a separate hand-held meter, so much the better.
Light meters live is a gray world, 18% neutral gray to be exact. A sage somewhere determined that the average brightness of the world is 18% neutral gray. Thus, all light meters strive mightily to record images that are 18% neutral gray. Most of the time this is fine. The scenes we photograph are often a mixture of bright and dim areas that probably do average out to 18% gray. But what happens when you photograph your snow covered house on a bright sunny day? Your meter thinks the scene should be gray. It is not. The scene is dazzeling white. If you followed the advice of your light meter (or let your automatic camera blindly select exposure) it would have you under expose your picture. The bright white snow comes out looking dirty and gray. Your meter did its job. It looked at a scene and created an exposure that makes the scene 18% neutral gray.
|18% gray is OVER exposed.||But the rocks ARE black, not gray.|
Your meter will also fail you in the opposite situation. Suppose you are at a concert and wish to photograph the events on stage. You are not in the front row. The performers are illuminated with a bright spot light. When you meter looks around, it sees all the darkness and only a little spot of light. As a result, the meter will tell you to over expose. The meters wants to turn all of that darkness into 18% gray. It will suggest a long exposure that turns the small spot lighted area into dazzeling whiteness. The performers are washed out while the the blackness becomes gray.
Unfortunately, we cannot do without light meters. Therefore, we must learn when to trust them and how to correct for their biased advice.
There are two types of light meters: those which measure the light reflected from a scene and those which measure the intensity of the light falling on a scene. Reflected light meters include automatic cameras and cameras with built-in meters. The second type, those which measure the light falling on a scene, are called incident light meters. An incident meter is more accurate and useful than a reflected meter. Clearly, an incident meter may only be used when you can physically walk up to your subject and measure the light. This limits their usefulness. An incident meter never knows whether your subject is reflective or not. It simply measures the intensity of the light reaching your subject.
A reflected meter allows you to keep some distance from you subject but, of course, assumes the subject is 18% neutral gray.
The goal of this discussion is not to master all of the intricacies of light meters. It is to make you aware of how they work and why they may not always give you the exposure that you really want. They are simple devices. A light meter is no substitute for a thinking photographer. The meter is not intelligent (despite the advertisements). It provides a useful opinion. You must decide whether to accept the opinion or supply corrections to better handle fast-moving subjects, depth-of-field challenges, or scenes with great contrast.
For tricky situations, take a couple of extra shots. First make your best guess at a correct exposure. Then take one slightly over exposed and another slightly under exposed. This technique is called bracketing. It is better to use a few extra pieces of film than it is to miss getting a good photograph.
|An exposure meter is pretty useless for a scene like this. The best bet is to make a series of exposures ranging from over-exposed to under-exposed.|
One note of warning is necessary: when using negative films, the photo lab projects the negative image on to a piece of photographic paper. For this exposure, the printing equipment uses a special light meter which may commit the same sins as the light meter in your camera. For example, take the bright snow scene. You may opt to use a wider aperture than recommended by your meter in order to keep the snow from appearing gray. Then, unfortunately, the meter in the darkroom printing equipment will over expose the paper in its effort to make the world 18% neutral gray.
What can be done? One option is to shoot with slide films (we will talk more about films next week). With slides, the image mounted in the little cardboard mount is the film that was in the camera. The film is simply processed and mounted. No intermediate exposures are involved that mask your decisions.
Another option is to learn to look at your negatives and judge for yourself when the image recorded on film is of the correct density. The quick print from the one-hour processing lab will tell you if your image is sharp and if the composition is good. If the photograph deserves enlarging, take the negative to a custom photographic lab.
In photographic composition, there is really only one rule: Think! The vast majority of people who take pictures never think for a moment about what they are seeing in the viewfinder before they snap their picture. Once a person begins to think, the rules of good composition become self evident. With that comment in mind, the following will be some quick suggestions. Never follow any rule if, after careful thought, you deem your idea superior. In general, the guidelines of good composition are simple. More importantly, they work. Follow them to begin with. Once they become second-nature you may begin to transcend the rules.
Use the entire photograph. Placing your subject in the geometric center of your view finder is not pleasing to the eye and does not efficiently use your picture space. Avoid the center. Before you snap the shutter, check all four corners of the finder to see that you are properly using the space.
Try to frame your subject in such a way as to direct attention toward the subject.
When possible, accent any diagonal lines in your scene. Diagonals are great for directing attention and for adding tension to your photograph. Diagonals are visually exciting because they play against the rectilinear edges of the photograph. Nothing can rivet attention as powerfully as a set of converging lines.
If your subject possesses curvature, try to compose in what is called an S-curve. This is visually interesting and works like a meandering diagonal.
Eliminate distractions. Identify your subject and emphasize only the subject. It is best to communicate only one idea per photograph. A written sentence that does too much is called a run-on sentence and is considered poor English. A run-on photograph is bad photography. Keep each photograph simple. Remove unnecessary elements. Move in closer if required.
Keep your backgrounds clean. If possible use a depth-of-field that will show clearly only your subject. Allow distractions in the foreground or background to remain out of focus.
In landscape photography it is usually best not to bisect your photograph with the horizon line. If you are photographing sky, put the horizon in the bottom third of the frame. If you are photographing land, why include one-half picture of empty sky? This issue of horizon placement is really just a special case of the first rule: use the entire frame.
A photograph should be complete unto itself. Do not allow picture components to trail off the edge of the photograph. This is especially true of portraits. Try not to cut off people's legs, arms, and hands.
Accent creative lighting. Light from the side or rear of your subject adds texture and depth to the composition. For landscapes, early morning or late afternoon are splendid times.
These guidelines may seem excessive. They are! All rules are covered by the first suggestion: Think! Resist the urge to snap without composing. Make photographs. Don't take pictures. Exercise as much control as possible. When you have an interesting subject, think of an interesting way to photograph it.
The branches in the forground add depth and focus attention.
This scene is obviously framed. It's also simple and direct.
Strong diagonal element and an interesting angle
This picture is obviously about SKY! It would be an entirely different photo if the subject were positioned smack in the middle of the frame.
This was exposed to accent the color in the clouds and the diagonal simply adds visual tension.
The shallow depth-of-field is all that makes this picture "work." A chipmonk sitting on a rock is too commonplace to be interesting. The shallow depth-of-field creates the green halo.
Without being at all obvious, the curve leads your eye across the photograph. The hiking party merely adds punctuation and scale to an expansive scene.
Make two photographs of a given scene, once with great depth-of-field, once with little depth-of-field.
Photograph a contrasty scene. Expose for the bright part, darkest part, and mid-range.
Exercise the principles of good composition by making photographs in which:
In all of these, eliminate distractions and keep the composition simple.