Digital Photography/Focal length


I read somewhere as
Focal length: 3,85mm (equivalent to 37,0mm)
Why there is two figures like 3.85mm & 37.0mm please explain.

Hi Raja

The focal length of a lens (for Digital Cameras)is always measured on a Full frame camera. A full frame camera is one, where the sensor size is equivalent to a 35 mm film negative. In any 35 mm film camera, a 28 mm lens is a wide-angle lens, and a 200 mm lens is a long-focus lens.

However, now that digital cameras have mostly replaced 35 mm film cameras, there is no uniform relation between the focal length of a lens and the angle of view. Since the camera sensor size determines angle of view and the sensor sizes are not standardized in all Digital camera, unlike a 35 mm film, the 35 mm equivalent focal length of a particular lens–sensor combination is the focal length that one would need for a 35 mm film camera to obtain the same angle of view.

A Full frame DSLR sensor (Eg: Canon 5D Mark II) is 36 x 24 mm in size, an APS-C DSLR sensor (Eg: Nikon D5100) is 23.6 x 15.6 mm and Point & Shoot cameras' sensor (like Sony HX 200v) is 6.17 x 4.55 mm. Since the size of the sensors are different, the focal length will also vary accordingly. Thus, to standardize the focal lengths and allow us to compare different cameras, the focal length is always compared as 35 mm equivalent.

Please feel free to get in touch for any more queries.



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Vipin Joshi


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