If, however, we mounted a 50mm APS-C lens on a FF camera, the image circle may not be large enough to cover the entire sensor. one lens might be t/1.8 at f/1.4 and another t/1.6 at f/1.4 one might have 2 stops of vignetting at f/1.4 and another might have 3 stops of vignetting at f/1.4). For example, a 50mm FF lens at f/1.4 on the APS-C camera will result in the same exposure as a 50mm APS-C lens at f/1.4 on an APS-C camera (barring in differences in t-stops and vignetting - e.g. In addition, the f-numbers will have the same effect. one 50mm lens might actually be 48mm and another might actually be 52mm). Therefore a 50mm lens on a 2X crop body is sometimes called "100mm equivalent", even though the lens remains a 50mm focal length lensĪ 50mm FF lens mounted on an APS-C camera will give the same angle of view as a 50mm APS-C lens mounted on an APS-C camera (plus or minus slight differences between the actual focal length and marked focal length - e.g. Therefore any combination of lens/body that results in a 24° angle of view, may be called "100mm equivalent"Ī 50mm lens on a 2X crop body is one combination that yields that 24° angle of view. The crop body lens will likely vignette more, but the difference won't be noticeable on a crop body.įor historical reasons, Angle of View is frequently expressed in terms of the corresponding focal length for a 35mm film SLR.įor instance a 100mm lens on a 35mm film SLR yields a 24° angle of view. The difference between a 50mm full frame and 50mm crop body lens is not related to the angle of view. In both cases the focal length remains 50mm. That same lens on a 2X crop body will yield a 24° angle of view. A 50mm lens is always 50mm, no matter which body it is mounted on (and even if it is not on any body).Īngle of view is determined by both focal length and sensor size.Ī 50mm lens on a full frame body will yield a 47° angle of view. The fundamental problem is that "focal length" is not a good way of describing "angle of view".įocal length is a physical property of the lens, and is independent of the sensor size. I hope that I explained my question clear enough and I thank you in advance. So let's say I have a 50 mm APS-C lens and a 50 mm full-frame lens on a crop sensor camera - will the focal length be ~80mm on both lenses or is it 80 mm on full-frame and 50 on APS-C? But are the numbers on the APS-C lens already 'calibrated' or does the same rule apply also for these lenses? I do understand that a full-frame lens on a full-frame camera is not the same as on a crop sensor camera. I'm struggling a bit with understanding the crop sensor/full-frame in a specific case and would appreciate your help. so if you could put my 35mm macro on a 4/3 sensor camera it would behave like a 70mm This ratio of sensor diagonals is called the "crop factor". The interaction is predictable The field of view on a smaller format than FF is always the same as that of a lens on FF whose focal length is equal to the focal length of the lens used on the smaller format multiplied by the diagonal dimension of a FF sensor and divided by the diagonal dimension of the smaller sensor. Even these manufacturers do engrave actual focal lengths on their lenses though.įor example I have an APSC only 35mm Macro, the focal length is 35mm but the field of view (al la pic above) means it behaves like a 50mm on APSCįocal length is defined by the lens design,įield of view is dicated by the sensor sizeĪnd its interaction with the focal length. Many of these will refer to their lenses in FF equivalent focal length (but never mention FF equivalent apertures). While that may be true of manufacturers of APS-C and larger format cameras, it is not always true of makers of smaller format systems. Manufacturers alway (I think) refer to a full frame focal length when describing lenses, even if that lens cannot be used on FF
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