Focal length of the eye
- It’s often argued that the standard lens1 is closest to how the human eye perceives things, though this is debated. Personally I find a slightly wider lens to work better for me, with a 35mm lens on 35mm film being easier to work with.
- But what is the actual focal length of the human eye?
- Turns out, this has already been calculated , and it’s not close to a standard lens. The object focal length is about 16-17mm, and the image focal length is about 22-24mm. Much better. The object focal length is for rays coming out of the eye, while the image focal length is for images formed on the retina2.
- Does this explain my preference for wideangle lenses? Probably not.
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This is defined by the diagonal width of the sensor or film image. It should be 42.3mm for 35mm film, though in general, somewhere between 45mm and 55mm is used in practice. ↩︎
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Julia Khutoretskaya, “Focal Length of a Human Eye”, The Physics Factbook, ed. Glenn Elert, 1997–2007, accessed 9 March 2026, https://hypertextbook.com/facts/2002/JuliaKhutoretskaya.shtml . ↩︎