Stefan Ahlblad
(C) Stefan Ahlblad 2015 All rights reserved 
original 50mm
cropped to 135mm
original 135mm

Sensor size and focal length

This page is intended to clarify the impact of using full frame lenses on a cropped sensor camera. To emphasize the impact I am using images taking with a 50mm and a 135mm lens rather than with a 50mm and 75mm lens which would match the relation between the APS-C  and the full frame sensors.

The focal length of a lens is specified in the same units  of mm regardless of whether the lens is intended for a full frame DSLR/ mirror-less camera or a camera with a smaller image sensor such as an APS-C sensor. This means, for example, that the image produced using  a “normal” 50mm lens on a APS-C sensor camera will be cropped to a size resembling a 75mm lens used on a full frame camera . However, the two 75mm images will not be quite identical. The latter, or the actual 75mm lens, will have shallower depth-of-field. A full frame 50mm lens used on a cropped sensor camera will also produce a slightly less sharp image than a 75mm lens on a full frame camera (assuming the two sensors have the same pixel density and the lenses used are of approximately the same quality.) There is one  benefit of using a full frame lens on a cropped sensor camera. Unsharp edges and corners produced by the lens will be cropped out. Unsharp edges are common with most lenses particularly when using large aperture settings such as f/1.4-f/3.6.

s2-50.jpg s2-cropped.jpg s2-135.jpg s3-50.jpg s3-cropped.jpg s3-135.jpg s4-50.jpg s4-cropped.jpg s4-135.jpg s6-50.jpg s6-135.jpg s6-cropped.jpg s5-135.jpg photos4001001.jpg lenstest.jpg page%201.jpg photoalbum.jpg videos.jpg abc.jpg art.jpg credentials.jpg s5-50.jpg