Aperture Shutter Speed
A correct exposure is the combination of the following factors: aperture (f stop), shutter speed, and ISO. These three settings make up the Exposure Trinity, or the Photographic Triangle as it is sometimes referred to. No matter how you spell it out, the combination of these three factors will make or break the image.
You will need to become familiar with the various aperture settings that your lenses are capable of. If you have a fixed zoom lens on your camera, you are probably limited to f/8. If you have a DSLR, you will have a wide assortment of lenses to choose from.
Some lenses are fast, and can have apertures as wide as f/1.2, or f/1.4, while others may have a maximum aperture of f/ 3.5 or f/ 4.5, these lenses are considered “slow” lenses. You will also be using the minimum aperture that your lens is capable of, so you will want to familiarize yourself with it as well—it might be f/16, f/22, f/32, or even as narrow as f/64.
ISO
F Stop
Since digital cameras have tremendous depth of field capabilities, DOF (depth of field) will always be a consideration. Before composing any shot, you will want to analyze the background and determine if you would like it to appear in the shot, and if so, to what degree. You will set your f-stop first, typically, and then set the shutter speed based on the speed that the meter determines is the “correct” exposure for the scene. Your meter will select a shutter speed based on the f-stop, and the current ISO selected. If you are shooting hand-held, you will need to know what the minimum shutter speed must be in order to ensure that the image will be sharp. The longer the lens, the faster the shutter speed must be in order to produce sharp focus.
Knowing the limitations of your camera and lens in the available light that you are shooting in is absolutely critical. If there is not enough light for you to shoot with a shutter speed that is fast enough to capture the subject in sharp focus, then you will have to either put the camera on a tripod, or raise the ISO. Obviously, by putting the camera on a tripod, you can solve most long shutter speed (as long as the subject is not moving) challenges. However, if the subject is moving, or if putting the camera on a tripod is not an option, then one must raise the ISO, or select a wider aperture. At this point, one must decide what is most important, maintaining the previously selected DOF (depth of field) with the current aperture, or reducing the dept of field by “opening up”.
If one decides that changing the depth of field is not an option, then raising the ISO is the only way that one can achieve a faster shutter speed. This is a prudent choice—up to a point. The point at which the digital noise of the high ISO will degrade the image beyond usability is the point at which one must reevaluate whether one can live with a change in the depth of field. One way or another, more light must reach the sensor if the shot is going to be fired at a shutter speed that is fast enough to hand hold the camera, and this can be accomplished by either “making the hole bigger”, or increasing the sensitivity of the sensor (which is accomplished by raising the ISO). Read More
