One of the most important factors governing the taking of superior pictures is correct exposure, which is the correct relationship between:
- Shutter speed, and
- Aperture (lens opening), as decided by:
- The brightness of the subject, and dependent on:
- The film or sensor sensitivity.
When either the lens opening or shutter speed, or both, are incorrect for the brightness of the subject matter, either under-exposure or over exposure is the result. Thus, it can be seen that it is very important to be able to judge the brightness of the subject correctly in order to obtain properly exposed pictures.
The aperture controls the amount of light that enters the lens and passes through to the image plane. The graduated series of lens opening are called "apertures" or "stops" and are controlled by revolving the aperture ring on the lens barrel, until the required aperture number is opposite the aperture index mark.
The standard lenses have the following apertures, with the exposure ratios noted, showing that the larger numbers are the smaller apertures:
The above table shows that each smaller aperture permits only one-half the amount of the next larger aperture and requires double the exposure. Stopping down will require a corresponding increase in the shutter speed if light conditions remain unchanged.
In other words, if the shutter speed is originally set at 1/60 second for f/8 aperture, it will be changed to 1/30 second if the aperture is stopped down to f/11 or to 1/125 second if the aperture is opened one stop to f/5.6.
Depth of field
The area of acceptable sharpness in the foreground and the background of the principal subject which is in proper focus is called the "depth-of-field" and the principles governing it are:
- The depth of field is greater as the diaphragm is closed down and least as the diaphragm is opened. The wide-open aperture of the fully automatic lens always shows the minimum depth of field.
- The depth of field becomes greater as the subject-to-camera distance increases and least at close focusing distance.
- The depth of field is greater in the background and shallower in the foreground but grows progressively equal as the focusing distance is increased.
- The depth of field increases with the use of a short focal length (wide-angle) lens and decreases with the longer telephoto lenses.
The depth of field scale on the lens barrel, shows at a glance the zone of apparent sharpness at any lens opening or distance setting and is utilized for quickly and simply ascertaining the depth of field.
The depth of field scale is next to the distance scale, and is made up of identical pairs of apertures on both sides of the distance index, which is also represents the widest aperture. These identical pairs of apertures indicate the distance that will be in focus at these lens openings.
For example, if you are using a f/11 lens opening and focusing on 10 feet (3 meters), read the distances opposite the figures 11 on both sides of the depth of field scale, which will be about 8 and 15, showing that the depth of field is approximately 8 feet to 15 feet (2.4 to 4.6 meters).
On the other hand, if f/11 does not give a sufficient zone of sharpness, check the depth of field scale to see which aperture does give you a broader depth of field. If, for example, it should be f/22, your zone will be seen to extend from approximately 6 feet to 30 feet showing that stopping down the lens will drastically change your depth of field.
Of course, since it also means that the shutter speed must be decreased to compensate for the reduction in the effective amount of light reaching the image plane, there are limits to which the lens should be stopped down.
An alternative and more practical method for finding a suitable aperture, when the zone of sharpness which must be used is already known, is zone focusing. In this method, don't focus on the prime subject, but first focus on the nearest important subject and note the distance setting. Next, focus on the farthest important subject and also note the distance. Now set these distance settings opposite identical aperture numbers or as near as possible to them.
For example, let's imagine that your nearest subject is 8 feet and the farthest 15 feet, as found on the distance scale. Turn the distance focusing ring until these figures come opposite identical numbers (f/11 in this case) and you are all set.
When there is not enough time to find the extreme limits for the above zone focusing method, a rough but faster method is also possible. Since it is known that the foreground is more shallow than the background (except in close-up shooting where a shallow depth of field prevails anyway), focus on a subject about two-fifths of the way into the required zone of sharpness and choose an aperture which will be consistent with the overall field.
Since the lens proper is the viewing-focusing system of the camera, all focusing adjustments are made directly on the lens itself. To obtain sharpness of the image, the focusing ring is turned fore and aft until the image becomes sharp. The lens-to-subject distance can then be read off on the distance scale immediately behind the focusing ring, against the single index mark.
For distant views without any foreground interest, set the focusing distance to infinity and the aperture to f/5.6 or f/8, as this will give maximum sharpness in the far distance.
Don't focus so that the farthest limit of the depth of field just reaches infinity. In this case, the lens would be focused on the near infinity point or hyperfocal distance and the acceptable range of sharpness would extend from the farthest limit to as far as possible in the foreground instead of being sharp only in the far distance.
For distant views (landscapes) with foreground interest, focus on the foreground subject and the far distant view. Set the distances thus obtained against the depth of field scale until they are opposite identical aperture figures. Use the aperture and distance obtained in this way, and there will be sufficient depth of field to cover the picture required.
Don't focus on the mid-point because the foreground is shallower in depth of field than the background and you will be focusing on a farther point than sufficient for covering the foreground subject.
For most landscapes, try to insert some foreground interest, particularly of human subjects. This will give your picture greater impact, story-picture value and even three dimensional effect. Even dark foliage in the foreground, or deep shadows, will set off the lighter background landscape and give the picture greater strength.
When shooting interior or architectural pictures, focus on the near and far limits required to be covered. Set these figures against the depth of field scale to obtain the required aperture and distance. The aperture will usually be a small lens opening.
For portrait or close-up shots, work with a comparatively large aperture and focus on the center of interest, such as the subject's eye. This will produce a very shallow depth of field, for placing emphasis and dramatizing the center of interest, while, at the same time, making it stand out sharply defined against a subdued and diffused background. Furthermore, use a neutral colored and uncluttered background, or move the subject away from the background, or use the sky as the background (if shooting outdoors) and take your pictures early or late in the day when the light is softer than the midday sun.
Use zone focusing for sports shots, actions within a limited area or sudden snap shots, when you find little time for accurate focusing. Set your aperture at f/8 and shutter speed according to prevailing conditions. Set distance at 10 feet which will give a depth of field of 8 feet to 15 feet. Under most conditions shutter speed should be about 1/125 to 1/250 second, sufficient for most fast action.
If your particular requirements calls for a larger depth of field, set the limits of your zone against the depth of field scale and find your aperture and distance settings, but choose an aperture which will give you a sufficiently fast shutter speed.
If zone focusing is not possible for fast action shots because the selected shutter speed requires a large aperture and results in a shallow depth of field, use pre-focusing.
Focus on the spot that the subject will pass and snap the shutter at the right moment.
Use the widest aperture for its selective focus ability, for placing emphasis where it is required, for dramatizing the center of interest, for eliminating distracting background and for greater directional impact.
Use the smallest aperture for its covering power from a few feet away to the far distance and for its ability to gather all the separate elements together and organize them into a more effective picture.
Move in for close-ups of a part of the subject, which will cover the full picture frame, with added impact and drama, and change the commonplace subject into a more powerful picture.
Choice of shutter speed is entirely dependent on the requirements for stopping the actions. Choose the fastest possible shutter speed to minimize camera vibration.
Choice of shutter speed for any moving object is dependent on:
- The speed at which the subject is moving; the faster the subject the faster the shutter speed;
- The distance of the subject from the camera; the greater the distance the slower the shutter speed;
- The angle at which the subject is moving in relation to the camera; movement towards or away from the camera requires a slower speed than movement at right angle to the camera, while movement at intermediate diagonal angles requires speeds between these two limits;
- The focal length of the lens used; the longer focal length shows an enlarged image moving at a faster speed than a shorter focal length from the same position and thus requires a faster shutter speed;
- The degree of "stopping" required; the fast speed of 1/1000 second can "deep freeze" most fast action but sometimes a blurred movement of the arms or legs will prove more effective in conveying the feeling of motion than if the motion is stopped "dead".
Panning the subject movement can also stop the motion, if exposure conditions do not permit a fast shutter speed, or if the blurred background will help to convey the feeling of motion more readily.
Move the camera with the subject and release the shutter while following the movement smoothly through to the end.
Catch the "peak" of the action with a slow shutter speed, if a fast shutter speed is not possible.
Since most actions have a beginning, a peak and an ending, with a momentary pause between each phase, try to catch the peak of the action which should also be the most interesting.
Use extra slow speed, with the camera set on the tripod and no special lighting set-up, for catching the "mood" of dimly lighted subjects or interiors. While the subject will not be seen as distinctly as in a flash-lighted picture, the subject will have a "mood" resemblance which will not be captured in an artificially lighted shot.