Nifty Fifty wrote:
The depth of field at 2.5/105mm is practically identical to that at 1.2/50mm, provided the distance is chosen so that the subject is the same size in both cases.
I'm not sure ... if magnification, i.e. filling of the frame with the girl's face, is the same, DoF depends on aperture (see attached equations where R is the magnification, or reproduction ratio, F the focal length and P the pupil factor) and @ f/1.2 we get less depth of field. Of course, to get the same framing, with the shorter lens you must be closer to the subject, and this alters perspective, along with the angle of view.
DoF (N is the aperture, e.g., 1.2, 2.5, etc.: CoC is the Circle of confusion that depends on the sensor/film size):
AoV (x is the size of the sensor/film, e.g. the diagonal):
Nifty Fifty wrote:
The depth of field at 2.5/105mm is practically identical to that at 1.2/50mm, provided the distance is chosen so that the subject is the same size in both cases.
I'm not sure ... if magnification, i.e. filling of the frame with the girl's face, is the same, DoF depends on aperture (see attached equations where R is the magnification, or reproduction ratio, F the focal length and P the pupil factor) and @ f/1.2 we get less depth of field. Of course, to get the same framing, with the shorter lens you must be closer to the subject, and this alters perspective, along with the angle of view.
DoF (N is the aperture, e.g., 1.2, 2.5, etc.):
AoV (x is the size of the sensor/film, e.g. the diagonal):
Aug 30, 2026 at 12:58 PM
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