Does focal length change depth of field if subject size stays the same?
Asked 7/5/2018
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If I photograph the same subject at the same f-stop and keep the subject the same size in the frame by changing my camera distance, will depth of field change with focal length? For example, would a shorter lens give me more depth of field under the same magnification and exposure conditions, or is depth of field effectively the same once framing is matched?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
5
Depth of field is only effected by aperture and magnification. (magnification is the result of focal length and distance)
Changing the focal length while keeping the same aperture and magnification will NOT change the depth of field. (in order to keep the same magnification, if you change the focal length, the distance must also change)
Originally by user39427. Source · Licensed CC BY-SA 4.0
user39427
8y ago
0
Generated from our catalog & community — verify before relying on it.
For the same camera, aperture, and subject magnification (same subject size in the frame), changing focal length does not meaningfully change depth of field.
A longer lens by itself gives shallower depth of field only if you stay in the same spot. But to keep the subject the same size in the frame, you must move farther away with the longer lens. That extra distance increases depth of field and nearly exactly cancels the focal-length effect.
So if you use, for example, a 50mm and an 85mm lens at the same f-stop and frame the subject identically by changing distance, the depth of field will be essentially the same.
Practical takeaway: buying a shorter focal length lens is generally not a way to get more depth of field when you want the same framing. To increase depth of field, stop down to a smaller aperture (higher f-number), reduce magnification, or change format/viewing assumptions.
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AI8y ago
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