Sony DSLR-A700P Lenses and Accessories Selection Guide - Page 15

Glossary Angle of view How much of a scene fits into your frame is expressed as an angle of view, which changes according to focal length. A "standard" lens is one with an angle of view of about 47°, which approximates the scope of human visual perception. A wide-angle lens is a lens that has a wider angle of view, whereas a telephoto lens is a lens with a narrower angle of view. Depth of field 50mm F2.8 50mm F2.8 Depth of field refers to the area around your subject that appears to stay in focus. How "shallow" or "deep" it is can be independently affected by various factors such as aperture, focal length, and focusing distance. For example, depth of field gets deeper at smaller apertures, shorter focal lengths, or longer focusing distances. Conversely, it shrinks as you open the lens, use a longer lens, or get closer to your subject. Focal length A camera lens is constructed from many lens elements, but in principle it acts like a single Principal point of convex lens Focal Plane Focal Point Focal Length convex lens. Focal length is the distance (in millimeters) that light travels from the center of this idealized lens to where the image forms on the focal plane. Subjects appear larger at longer focal lengths, and smaller at shorter focal lengths. At any given focal length, the overall scope of the image will vary in relation to the size of the image sensor. F-stop F-numbers (or "stops") represent a ratio of the size of the aperture relative to the focal length of a lens. Because the aperture regulates the amount of light passing through the lens, each successive F-stop represents a halving or doubling of the brightness. Because an F-number is actually a fraction, smaller F-stops correspond to larger apertures. Lenses with smaller F-numbers are considered "fast" as they gather more light, permit the use of faster shutter speeds and provide a brighter viewfinder image. Magnification ratio Magnification compares the actual size of an object with how big the object appears on the image sensor. In macro photography, 1:1 magnification means that the object is just as big in the image as it is in real life. Lens specifications usually indicate the maximum magnification of a lens as either a rate or ratio. Perspective Perspective is the visual effect of how far apart foregrounds and backgrounds appear with respect to each other. It can be seen clearly in images taken with a wide-angle lens: foreground objects are big while background objects look small, which creates a sense of distance between them. This effect diminishes at longer focal lengths, as the distance between foreground and background gets compressed. APS-C size image sensor vs. 35 mm format Image area of 35mm format 47˚ angle of view Image area of DSLR with APS-C size sensor 32˚ angle of view Lens Focus Point Principal point Same focusing distance (50mm) Lens Focus Point At any given focal length, a digital SLR with an APS-C size image sensor has a slightly smaller angle of view than a 35 mm format camera, and yields an image that is about two-thirds in size. So if you are shooting with an APS-C format camera, it is useful to keep in mind a conversion factor of 1.5x. For example, a 50 mm focal length is equivalent to 75 mm in 35 mm format. 28 Accessories Expand the range of what, how and where you can shoot with system accessories for your camera. Available accessories include a variety of high-performance flash units, cables, and connectors, as well as viewfinder optics, carrying cases, and other essential items. 29