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Message: <blockquote data-quote="Bengt Nyman" data-source="post: 476401" data-attributes="member: 13692">J-see, correct.A 35mm FX lens has an actual, physical, optical focal length of 35mm. This is a true optical measurement. On other formats the advertised focal lengths have been adjusted to mimic the results of an FF camera. An "apparent 35mm DX lens" would not have a physical focal length of 35mm but a physical focal length of 52.5mm, which is why it "becomes" a longer lens when you put it on an FX camera.You can make the same argument in terms of field of view, but that does not as clearly reveal the truth about actual, physical focal length.A popular way to look at it is in terms of "crop factor" which unfortunately neither clarifies the physics behind it.</blockquote>