Does lens distortion change with focus distance?
Asked 3/7/2017
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2 answers
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For photogrammetry and calibration work, I’m trying to understand whether distortion parameters stay constant when using the same lens at a fixed focal length but changing subject distance/focus. If the camera/lens setup is otherwise unchanged, do distortion correction factors vary as the subject moves in and out of the focal plane, and should calibration be done at a particular focus distance?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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In short, yes the focus distance has an impact on calibration parameters. For further information on that, refer to this paper by D. C. Brown on Close-Range Calibration. Generally, it is advised to have the camera focused at infinity when capturing photographs for calibration purposes. To do that, you simply have to calculate the hyperfocal distance for your camera. There is an Android app that has many preloaded camera setups called Hyperfocal that does just that.
Originally by user47885. Source · Licensed CC BY-SA 4.0
user47885
9y ago
0
Generated from our catalog & community — verify before relying on it.
Yes — in practice, distortion calibration can change with focus distance.
Community answers point out that for ordinary lenses, object distance affects the effective mapping of the scene onto the sensor. As focus distance changes, you can see effects such as focus breathing (a change in image magnification) and changes in aberrations that influence measured distortion. So a calibration made at one focus distance may not be fully accurate at another.
An important exception is a lens designed to be image-space telecentric and essentially distortion-free; those are much more stable for measurement work.
For photogrammetry, the practical takeaway is to calibrate the camera in the same focus/working-distance conditions you will actually use, or keep the lens fixed at a known setting. One answer also notes that calibration is often done with focus set to infinity, using sufficient depth of field/hyperfocal distance where appropriate.
Also, very close subject distances can introduce strong perspective effects that may look like extra distortion, especially with wide-angle lenses, even when the lens itself is behaving normally.
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