Principles of the Lens

Principles Of The Lens

What you should know to choose the right lens for your needs

Angle of View and Focal Length

Angle of View and Focal Length

Angle of View

Angle of view is determined by the focal length of the lens and the size of the image (sensor or film format) frame. With a given image size, changing the focal length will change the area of the scene that appears in the photographic image. Expressed in degrees, this area of the scene is the angle of view, which in this catalog, is computed in reference to the diagonal of image formats measuring 36 mm x 24 mm, 20.7 mm x 13.8 mm and 23.55 mm x 15.7 mm. The longer the focal length, the smaller the angle of view and the greater the image magnification.

Aperture, F-stops and Lens 'Speed'

The aperture controls how much light can be gathered by the lens. The lower the f-stop (F2.8, F4, F5.6, etc.), the larger the aperture and the more light it will transmit to the image sensor. A so-called “fast” lens (low f-stop at maximum aperture), lets you shoot with less illumination, use a faster shutter speed, or more easily create defocused bokeh effects, not to mention providing a brighter viewfinder image. F-stops represent focal length divided by effective aperture diameter.

Perspective

You can control perspective by moving nearer or farther from your subject and then choosing a lens that frames your subject the way you want. To compress the distance between foreground and background, step back and use a telephoto lens (or zoom in). To spread out the background and emphasize distances, get closer and use a wide-angle lens (or zoom out). The telephoto isolates your subject, while the wideangle lens includes the subject’s surroundings.

Depth of Field

When you focus on a subject, some objects in front of and behind the subject will also be in focus. “Depth of field” refers to the depth of this foreground-background distance. A smaller lens aperture (higher F-stop), increases depth of field, bringing more foreground and background into focus. A larger aperture (lower F-stop) isolates your subject with a blurred “bokeh” foreground and background. Focal length is also a factor. Telephoto lenses have less depth of field, wide-angle lenses have more.

F2.8

F2.8

F22

F22