# Where are the principal planes located in a camera lens?

I want to find locations of the principal planes of a camera lens. I have looked at the specification for my lens here and here, but did not find what I need.

But there are many other parameters in the spec — can I use them to achieve principal planes?

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In English, "lens" in photography is used for what is called "objective" in other languages. An "objective" (the thing you mount on your camera) contains multiple true lenses inside, and they all move when you change the focus and zoom. So there is no way to point to a place on the outer skin of the objective and say "here is the principal plane". But out of curiosity, why would you want to know that at all? – rumtscho May 24 '12 at 18:41
I mean exactly camera lens en.wikipedia.org/wiki/Camera_lens (clarified question, hope I don't misuse photo-terms somewhere else). If you move optic lens the whole properties of camera lens are changed, but if you fixed them - this is thick lens - system of such lens: en.wikipedia.org/wiki/Lens_%28optics%29 (lens have many meanings :) ). In shot I need it to update existing procedure for more precise setup of focal length. – sergtk May 24 '12 at 18:51
You can use parallax to locate the nodal point of a lens (see for example dgrin.smugmug.com/gallery/2114189). Maybe also panoramabrackets.com/images/cameranodalpoint.pdf – James Youngman May 24 '12 at 23:18
@James Youngman I found in wikipedia that this is common misundestood en.wikipedia.org/wiki/Cardinal_point_%28optics%29#Nodal_points . Anyway thank for the link, hope these two points are not far from each other – sergtk May 25 '12 at 0:22

When the lens is focused at infinity, the sensor lies right on the image-side focal plane, and the corresponding principal plane is one focal length from that plane, towards the lens body.

There is no simple way to find the object-side principal plane. It's not on the specs. You may be able to calculate its position if you have the optical formula of the lens. If you have the actual lens, you may also measure the position of the object-side focal plane by reversing the lens and imaging a faraway object. The corresponding principal plane is again at one focal length from the focal plane.

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