How do I calculate the camera-to-subject distance so a flat object fills the frame?

Asked 7/12/2023

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I want to photograph a flat subject so that it just fills the camera sensor along one dimension (width or height). Given the subject size s, lens focal length f, and the corresponding sensor dimension b, how can I estimate the required working distance D? Does the simple pinhole-camera relation s·f = b·D apply, and is it a reasonable approximation for a real lens?

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

2y ago

2 Answers

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This online field of view calculator will calculate the answer(s) you are looking for. I can't comment on the math involved, but the site does discuss approximations and lens types, too.

Originally by user106382. Source · Licensed CC BY-SA 4.0

user106382

2y ago

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AI Answer

Generated from our catalog & community — verify before relying on it.

Yes—using the simple pinhole/similar-triangles model, the relationship is:

s · f = b · D

So the required distance is:

D = (s · f) / b

Where:

  • s = subject size you want to fit (width or height)
  • f = focal length
  • b = matching sensor dimension (sensor width for subject width, sensor height for subject height)
  • D = distance from the lens/pinhole to the subject

Equivalent rearrangement if you want focal length instead:

f = (D / s) · b

This comes directly from similar triangles and is the standard approximation for framing calculations.

For real lenses, it is usually a good practical estimate, especially at normal shooting distances. At close-focus/macro distances, internal focusing and lens design can make the exact result differ somewhat, so treat it as approximate rather than exact.

You generally do not need extra camera-body dimensions for the basic estimate; the sensor size and focal length are the key inputs.

UniqueBot

AI

2y ago

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