Shutter speed and aperture for constant exposure.
The f-stop (a calibrated setting for an f-number) is a measure of the size of the aperture (opening which the light passes through). The higher the f-stop the smaller the aperture (Figure 5).

Dividing the focal length of the lens by the effective diameter of the lens aperture mathematically derives the f-number. The higher the number the less light allowed through the lens (the smaller the aperture).

As the f-stop increases the amount of light is cut in half at each full stop (f 4, f 5.6, f 8, f 11, f 16, f 22, f 32) and is doubled as it decreases. The same is true for shutter speed (1/30, 1/60, 1/125, 1/250, 1/500), each is a factor of 2 or ½.

This is how you can control the exposure. The importance is that if you know the exposure at a given shutter speed and f -stop then you can calculate the exposure at a new shutter speed or f -stop. You will want to use this in cases where you want to change your depth of field or affect the action of a moving object.

The higher the f-stop the greater the depth of field.
The depth of field is the amount of distance that appears in focus. The higher the f -stop the greater the depth of field. In portrait photography we typically want a depth of field that is just enough to get the subject in focus about the face but blur the background. You can adjust this feature for various effects. In our intra-oral clinical photography, we want to maximize our depth of field (using the highest f -stop, the smallest aperture possible). The depth of field comes toward you as well as away from you (usually about 1/3 toward and 2/3 away from an object that appears in focus in the view finder).

Automatic verses manual exposure control and focus.
Whether you are setting the exposure manually, using the camera's built-in exposure meter, an incident light meter or letting the camera adjust automatically, the underlying principles are all the same. The difference in which mode to use will be determined by how much control over the process you want to have. The quality of the result will help determine what means best fits a given situation. Once you understand the basics of photography and gain some experience, the use of the manual mode will give you maximal control over the result and gives you the widest artistic latitude.

Your camera may have several choices of automatic exposure control, some of which the parameters you can adjust and set into the camera's memory for customized control.

Various manufacturers may use different terminology for exposure controls, but essentially they are all the same.

Dr Rhys Spoor DDS Aesthetic / Restorative Dentistry - Providing services in cosmetic and sleep dentistry to the area of Seattle, Washington.

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