BetterPhoto Q&A
Category: New Answers

Lens

To love this question, log in above
August 16, 2003

28-70MM refers to the focal length of this zoom lens. Less than 35mm gives a wide angle view, between 40 and 65 is considered a "normal" view, and 70 and longer is considered telephoto which gives a very narrow view (also "brings distant objects closer"). A "zoom" lens lets you vary the focal length. Other lenses may have just a single focal length, called fixed focal or prime lenses.

The numbers 1:3.5-4.5 are ratios and refer to the maximum aperture of your lens. Wide apertures let in more light (allowing faster shutter speeds) and have a very narrow range of apparent focus (also known as depth of field), so your subject will stand out against a blurred background. Smaller apertures let in less light (allowing longer shutter speeds), but the depth of field is great so that objects both near and far are in apparent focus. The aperture is given as a ratio to the focal length (stated as 1:xx or f/xx) so that the same aperture setting gives the same amount of exposure, regardless of the focal length of the lens. Because it is a ratio, smaller numbers refer to larger apertures. f/2 is a larger aperture than f/4. It is less expensive to make a zoom lens with a variable maxiumum apertue, so 1:3.5-4.5 means that the maximum aperture is f/3.5 at the 28mm end, but only f/4.5 at the 70mm end (and f/4 somewhere inbetween). Prime lenses and more expensive zooms will have a single maximum aperture that is available at all focal lengths.

"Macro" is a term that lens makers use loosely, but it generally means that the lens will focus to very short distances so that you can get large magnification close-ups. On a relatively inexpensive zoom such as the one you're asking about, it usually means that you can focus close enough to produce an image on the film frame that is 1/4 to 1/2 (also stated as 1:4 and 1:2) life size. There are more expensive specialty macro lenses that are designed to focus even closer and give full life size (1:1) or larger images on the film.

To love this comment, log in above
August 19, 2003