Finding The Nodal Point of Your Lens

Tutorials and ReviewsTutorials and Reviews ModeratorRegistered Users, Retired Mod Posts: 138
edited May 18, 2005 in Tutorials
Finding The Nodal Point of Your Lens

Tutorial by David_S85.


To eliminate the possibility of parallax errors (things not lining up properly) when stitching individual frames into panoramics, it is necessary to calibrate your panoramic head for the lenses and focal lengths you frequently use.

In this example we will calibrate a Really Right Stuff MPR-CLII nodal slide for a Canon 10-22 lens at 22mm in portrait orientation for use with the RRS L-bracket, and PCL-II panning clamp atop a BH-40 ballhead.

The basics described here should apply no matter what equipment you use. I should mention this tutorial is meant as a guide for single-row panoramas.
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An L-plate made for your camera model allows a convenient and accurate method of quickly locating the lens' center line whether you're mounting the camera in landscape or portrait orientation. Just line up the markings and tighten it up.

Both the slide and clamp have built-in levels (see last photo) to assure an accurately centered horizon line as you pan around.
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OK, so lets get busy determining the proper setting for our 22mm example.

Make sure the head is level.

We will place a couple of test targets in front of the lens and adjust the slide forwards and backwards with trial and error to eliminate parallax.
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Our willing test targets set firmly (they're taped down!) on a table. Initially, they should line up perfectly while your camera is pointed straight ahead. One is very near; the other about a meter farther away. The rear target is a little higher up so I could see both in the viewfinder.
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Loosen the lock on the PCL-II panning clamp and swing the upper rig left and right noting the alignment of the targets. In this case the slide is too far back. The bad alignment is caused by parallax error (what we're trying to avoid).
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Let's try another slide position...
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...This isn't good either. The nodal slide is too far forward and we have the opposite problem.
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Success! No parallax error here. This setting is a winner. The two targets line up exactly no matter which way we swing the rig. Write this setting down somewhere.

Repeat for each lens and focal length you might use for your panoramas.

Notes:
If you use zoom lenses, a lens' optical center (frequently and incorrectly referred to as the nodal point) changes for each focal setting. This means you'll need to calibrate for all frequently used settings. With my Canon 10-22, I have nodal slide settings for 10, 17, and 22mm. Oddly, the 10mm position is in between those for 17 and 22.

http://dgrin.smugmug.com/Tutorials/Shooting-Tech-and-Tips/Finding-The-Nodal-Point-of/slide2/109881517_3ZDaH-O.jpg

A post-it tape chart is attached directly to the slide to look up often-used settings. These figures include the focal length, its nodal slide position, how many degrees to swing the upper rig for proper shot overlap and the number of shots I'll need for a full 360º pano if I decide that's what I want.
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