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What is crop factor and how do I calculate it for the Russar+?

For digital camera users, crop factor refers the ratio of a digital camera’s sensor to a 35mm film camera. A full-frame digital SLR has a sensor size is roughly equivalent to a 35mm film frame (24mm x 36mm). A camera with a smaller sensor captures only a portion of the image that a full frame sensor would, due to the fact that the small sensor magnifies the angle of view.

If you multiply a lens’s focal length by the camera’s crop factor, you get the “equivalent focal length”, which is the focal length needed to produce the same angle of view on a 35mm camera. You will get different photos depending on the lens and camera according its sensor size.

Sensor sizes vary by manufacturer but in general there are three standard crop factors:

APS-H crop sensor (Canon 1D series, Leica M8) has a crop factor of 1.3.
Equivalent focal length with the Russar+ 20mm Lens = 26mm

APS-C or Nikon DX crop sensors (Fujifilm X, Sony E, Ricoh GXR, Pentax K) 1.5
Equivalent focal length with the Russar+ 20mm Lens = 30mm

Micro 4/3 crop sensors (Olympus PEN and
Panasonic Lumix families) with a crop factor of 2.0
Equivalent focal length with the Russar+ 20mm Lens = 40mm.

Photo taken from discoverdigitalphotography