F-stops, Focal Length and Lens Aperture Options

photoling Posts: 422 Points: 1623
Posted: Saturday, August 12, 2017 11:28:27 AM

Sensors from different manufacturers vary widely in size, but in general they're smaller than a piece of 35mm film. In order to project the image onto a smaller sensor, the focal length is shortened by the same proportion.

If your camera has an APS-C sensor (Nikon DX DSLRs, Sony NEX…) it has a crop factor of 1.5 - meaning you multiply the lens focal length by 1.5 to get its equivalent 35 mm-format focal length. For Canon APS-C cameras that number is 1.6, for Micro Four Thirds cameras it's 2.0 and for the Nikon 1 series it's 2.7. That means a 35 mm lens would give a field of view equivalent to 56 mm on an APS-C camera like a Canon 70D and equivalent to 70 mm on a Micro Four Thirds camera like the Olympus OM-D E-M1.

photoling Posts: 422 Points: 1623
Posted: Tuesday, January 1, 2019 2:15:19 PM

35mm cameras, a 50mm lens gives a natural view of the subject. Increasing the focal length increases the magnification, and objects appear to get closer.

photoling Posts: 422 Points: 1623
Posted: Thursday, January 3, 2019 11:05:57 AM

The following table provides an overview of what focal lengths are required to be considered a wide angle or telephoto lens, in addition to their typical uses.

Lens Focal Length* Terminology Typical Photography
Less than 21 mm Extreme Wide Angle Architecture
21-35 mm Wide Angle Landscape
35-70 mm Normal Street & Documentary
70-135 mm Medium Telephoto Portraiture
135-300+ mm Telephoto Sports, Bird & Wildlife
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