Ambient Light:
Ambient, or available light refers to the light that already is present in the location where you plan to shoot. This light could be sunlight or indoor overhead lighting. Typically, when using studio flash units, the ambient light will be overpowered by the direct flash. However, it is important to factor in any ambient light in your flash meter readings to insure a proper exposure.
Aperture:This is referred to the lens diaphragm opening inside a photographic lens. The size of the opening regulates the amount of light exposing your image. The size of the opening is controlled by the f-number (1.8, 2.0, 2.8, 4.5, 5.6, 8.0).
Automatic Mode:The automatic mode is a setting on your camera that allows the camera to use its internal meter to automatically adjust the aperture and shutter speed for a shot based on the prescribed ISO speed of your film, and the available light. When using studio flash units, you can not leave your camera in automatic mode, as its internal meter will not be able to detect the light that will be emitted by your flash units, and will thus be set to an inaccurate shutter speed and aperture opening, causing your picture to be overexposed. Furthermore, when in automatic mode, many cameras have TTL metering which will send out an infrared signal to read the light, and that signal may inadvertently trip your unit's built-in slave tripper.
Bracketing:This is a common trick or technique used by film photographers. Bracketing is done by taking several photographs of the exact same scene and setup with different exposure settings. As different brands of flashmeter vary in their readings for a "correct" exposure, bracketing both above and below the indicated settings will ensure that you get a properly exposed picture. If, for example, the indicated exposure for a setup is f5.6 with a shutter speed of 1/60 second, you can bracket for one stop less at f8, and one stop more at f4.
Color Temperature:In image processing, color temperature (or color balance) is the global adjustment of the intensities of the colors (typically red, green, and blue primary colors). An important goal of this adjustment is to render specific colors - particularly neutral colors - correctly; hence, the general method is sometimes called gray balance, neutral balance, or white balance. Color balance changes the overall mixture of colors in an image and is used for color correction; generalized versions of color balance are used to get colors other than neutrals to also appear correct or pleasing.
Contrast:The contrast is the degree of difference between the dark and the light areas of a scene or photograph. High contrast photographs are a result of high contrast lighting, where there are sharp differences in the dark and light, and less in between. High contrast lighting can be achieved with both direct and bounced light that is not softened or diffused, but often reflected from a bright silver surface.
Depth of Field (DOF):Depth of Field is the portion of a scene that appears sharp in the image. Although a lens can precisely focus at only one distance, the decrease in sharpness is gradual on either side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions. The DOF is determined by the subject distance (that is, the distance to the plane that is perfectly in focus), the lens focal length, and the lens f-number (relative aperture). Except at close-up distances, DOF is approximately determined by the subject magnification and the lens f-number. For a given f-number, increasing the magnification, either by moving closer to the subject or using a lens of greater focal length, decreases the DOF; decreasing magnification increases DOF. For a given subject magnification, increasing the f-number (decreasing the aperture diameter) increases the DOF; decreasing f-number decreases DOF.
Image Stabilization (IS):You will most commonly see the letters IS or the words Image Stabilization attached to a lens name. For example: Canon EF 28-300mm f/3.5-5.6 L IS USM Lens. A lens with Image Stabilization will allows you to shoot at a lower shutter speed and still retain a sharp image. For example, you can often achieve the same results as shooting 1/200 with a regular lens, as shooting 1/20 with a lens with IS.
UltraSonic Motor (USM):The USM is Canon lens feature that is essentially a small motor within your lens that allows your lens to achieve a faster automatic focus. A Canon lens with a USM installed is generally more expensive and heavier.
