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The Curious Bag
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The numbers on a zoom lens can be confusing. Focal length, zoom range and minimum/maximum aperture are all important. Knowing how to interpret these numbers is a basic way to improve photographic skills.
Zoom defined
A zoom lens varies in focal length and is often confused with a telephoto lens. Zoom lenses are offered in many different configurations, including wide-angle and telephoto. Telephoto lenses have a fixed focal length and offer higher magnification than a normal lens.
Focal length
A zoom lens's range is defined by its focal length. The focal length of a lens determines its angle of view. A lens designated 70-210mm has a minimum focal length of 70mm and a maximum length of 210mm.
Aperture range
The aperture range indicates the largest aperture of the lens based on the chosen focal length. The aperture acts as an iris and allows light to pass through the lens into the camera. Zoom lenses often have larger maximum apertures at the shortest focal length.
Filter size
Filter size is indicated on the front of the lens barrel by the diameter symbol, "Ø," followed by a number. A lens with Ø 62 indicates that the measurement across the lens from rim to rim is 62mm.
Distance scale
This scale indicates how far away the lens is currently focused. This scale is used in conjunction with the f/stop range to estimate depth of field.
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