Some lenses have distance/ hyperfocal markings - is that with reference to the flange (outer mount point of the lens where it meets the camera body) or the film/sensor plane?

  • follow up: reason I ask - I build my own digital cameras - they do not have a viewfinder so i need to figure lens to sensor distance to make the approximate distances on the lenses i use useful. Flange distance is useful but since the sensors I use do not include the distance from the cover glass to the sensor i could easily be out +/-1mm .
    – ralph
    Oct 16, 2021 at 22:54
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    Given that rear lens elements can protrude into the body of the camera, the distance between the rear element and the sensor/film plane can vary.
    – Joanne C
    Oct 16, 2021 at 23:23
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    I'm curious as to what you're doing considering the lens markings are typically logarithmic meters and you need to account for +/-1mm? Oct 17, 2021 at 22:45
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    I would think that even with a perfect setup (for some definition of perfect) the width of the lens marker line and the mechanical slop of turning the focus ring from one direction verses the other would still be only a ballpark focus requiring a high F-stop or luck. Then again, less than perfect focus can still produce an acceptable picture. Good Luck! Oct 18, 2021 at 4:11
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    Does this answer your question? What is the reference plane used when the minimum focus distance is measured?
    – Michael C
    Oct 20, 2021 at 7:57

4 Answers 4


There are two similar, but distinct, concepts to consider:

Focus distance is the distance from the subject to the sensor plane mark on the camera body, which of course corresponds to the location of the sensor/film plane. A lens's minimum focus distance is usually specified, and is always with respect to the sensor/film plane mark. The distances markings or scales on lenses are this type of focus distance, measured from the focal plane marker.

Working distance is the distance between the front of the lens and the subject. Working distance is sometimes specified by lens manufacturers, and often reported by lens reviewers experimentally.

See also:


The sense of these marks is: if the object is on distance 3 meters and you set the focus (mark) on 3 meter the object will be in focus on the photo. So these marks are related to film/sensor plane.


Distance markings on lenses are from subject to focal plane (i.e., where the film or sensor is located).

  • I posted this since none of the existing answers seem to explicitly answer question.
    – dhag
    Oct 17, 2021 at 18:42
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    Read first sentence from the answer of scottbb, the you can read second sentence from my answer. Both of them explicitly say it! Oct 17, 2021 at 19:17

Focal length is a measurement, lens to focuses image when the object being images is at an infinite distance. The light rays from such a distant object, like a star, arrive at the lens as parallel rays. If the lens is a simple convex - convex lens, this measurement is made from the center of the lens to the focal plane.

Modern camera lenses are not simple, they are arrays of lenses. Some are cemented to its neighbor, some are air-spaces, some have positive power (converging) some have negative power. On an optical bench we find two cardinal measuring points. Focal length is measured from the rear nodal. Object distance is measured from the front nodal.

These two cardinal points are generally not listed in the specifications. The position of both can be discovered on an optical bench. These points are often inverted. A telephoto lens features the rear nodal making the barrel shorter thus the lens is less award. A wide-angle often shifts the rear nodal to allow a longer back-focus. This provides room for the mirror and other devices.

If you can achieve magnification 1 (unity or life-size) the focal plane is approximately 2X the focal length behind the rear nodal. The object distance is approximately 2x the focal length forward of the front nodal.

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