DSLR Beginner

18-55mm f/3.5-5.6 means that the lens has a lens speed of f/3.5 at the 18mm focal length, but a lens speed of f/5.6 at the 55mm focal length.

EF-S 18-55mm f/3.5-5.6 IS II is a standard zoom offering a 28.8-88mm equivalent focal length range.

Lens speed refers to the amount of light that travels through the lens while the shutter is open. This is controlled by the size of aperture. The faster a lens, the larger the maximum aperture in the diaphragm and the more light will hit the sensor at the same shutter speed.

Focal length is the distance between the point of convergence of your lens and the sensor or film recording the image. The focal length of your film or digital camera lens dictates how much of the scene your camera will be able to capture.

Lens focal length tells us the angle of view—how much of the scene will be captured—and the magnification—how large individual elements will be. The longer the focal length, the narrower the angle of view and the higher the magnification, and vice versa.

Depth of field is the distance between the closest and farthest objects in a photo that appears acceptably sharp. Large apertures, which correlate to small f-stop numbers, produce a very shallow depth of field, and vice versa. Another important factor affecting depth of field is the distance between the camera and the subject. The shorter that distance, the smaller the depth of field.