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Filed under: Cameras •Hardware •Production •Training •

Make the Entrance Pupil Your Friend

The easiest way to find the pivot point, or entrance pupil, of your lens is to set up the C-stands, as illustrated in the drawings, and then slide the camera forward or backward until panning the camera results in the front C-stand hiding the back C-stand for the entire pan. This means the lens will be somewhere over the rotation point of the head, so be prepared for the camera to want to fall over backwards unless the head is locked down extremely well.

Here’s how it will work:

Notice how the lens stays in the center of rotation, eliminating parallax errors during panning. Here’s the result in a moving picture:

This is the same setup as used previously, except that the focus ring on the 18mm Ultra Prime is now centered over the axis of rotation. That seems to be where the entrance pupil is located.

Finding the pivot point for panning is relatively easy. Doing the same for tilting is more difficult: if the camera is on a standard fluid head (like a Sachtler Video 20 or O’Connor 2060—other than an underslung head like the Weaver-Steadman head or similar) the rotation point is the middle of the head, and you can’t get the lens there. Geared heads may allow the camera to be raised so that the lens is in the center of the cradle’s rotation axis. Weaver-Steadman heads can be used to find the vertical pivot point with great success.

Be wary of anamorphic lenses, though. Such lenses are really a combination of two different lenses: for example, a 40mm anamorphic lens is 40mm in the wide axis but 80mm in the tall axis, creating a 2:1 squeeze. Such lenses have two pivot points, one for each lens, and they don’t fall in the same place.

I haven’t used this trick more than a few times, but at least I knew how to use it when it counted. And now so do you.

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Art,
Great article as usual!  Thanks man, keep them coming.

Posted by .(JavaScript must be enabled to view this email address)  on  08/05  at  11:58 AM

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good article…
so to use 3 red cameras
and not have parallax,
you have to either have them , by some miracle, inhabit the same space
or
shoot through mirrors

whats he gonna do??

i gots to know!

Posted by billS  on  08/08  at  03:56 AM

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