Eliminate Parallax
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| Nikon D200 with 50mm/f1.4 lens. Camera fitted with BD200-L plate; mounted on MPR-CL nodal slide and PCL-1 panning clamp. Note how nodal slide has been used to shift camera backwards so that optical center of lens can sit atop the axis of rotation (in this case, the center of the panning clamp). |
Even if your setup is perfectly level, you won't be happy with the results until you eliminate image parallax. Image parallax occurs when near and far objects don't align in overlapping images. For example, if you're shooting a scene that contains a fence line, each fencepost in Image 1 should line up with its twin in Image 2. You can eliminate the effects of parallax by placing the optical center of the lens (not the camera) directly over the point of rotation.
See image at right:
- Vertical red line: axis of rotation
- Horizontal red line: lateral centerline of lens axis
- Yellow lines: light rays cross in the optical center of the lens
You're ready to shoot panos when your points of intersection converge.
But how can you shift the camera and lens backwards when your camera body plate only slides left/right? Add one of our nodal slides. These long rails with built-in clamps mount to the bottom of your camera body plate and are the perfect way to shift your camera & lens back so that the optical center of the lens can be correctly positioned directly over the pivot center.
Optical Center? Nodal Point? Entrance Pupil?
There's friendly controversy over the correct term. But for the sake of visual simplicity, we'll stick to the terms "optical center" or "nodal point" when referring to the point about which your setup should rotate.
Parallax & Nodal Point Experiment
These concepts can be bewildering, but their influence on creating seamless panoramas can be demonstrated with a simple experiment rather than through an optics lesson.
Try the following experiment: With one eye closed, extend your arm and point your thumb up. Line your thumb up with the side of a door frame. Now, turn your head left and right. Notice how the door frame shifts as you turn your head? This is an example of image parallax due to the fact that the optical center of your eye is not over the center of your head rotation.
You can also do this experiment with a camera and attached lens (it's easier with a prime lens). Pivot the camera left and right over its tripod mount and you will notice the same effect as background objects shift relative to foreground objects (say, a nearby fence post versus a distant fence post). But if you pivot the camera at a specific point under the lens, you'll notice that the near and far objects remain aligned. We'll call this specific point of rotation the optical center of the lens. The idea is that parallax can be eliminated by mounting the camera on the ballhead so the optical center of the lens sits directly over the rotation axis of the ballhead.
Nodal Slides
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At top: MPR-CL Nodal Slide - great for prime lenses
Bottom: MPR-CL II - great for zoom lenses.
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Our most common nodal slides are MPR-CL (top image) and MPR-CL II. These nodal slides are perfect when you're shooting a pano with non-collared lenses (shorter lenses without a rotating tripod collar).
If You Shoot with Prime Lenses...
Lenses with a single focal length; e.g., 24mm/f2.8, 50mm/f1.4, 85mm/f1.8. Choose MPR-CL. The MPR-CL is 6-inches long (152mm) and weighs only 3.8-ounces (106g). When used as a nodal slide, the length of the MPR-CL is adequate if the nodal point is less than 110mm from the film plane/digital sensor (don't confuse focal length with location of the nodal point!). The nodal point in a prime lens tends to be close to the physical center of the lens (this is a generalization—your mileage may vary). This is the same mounting rail that is included with our Portrait Packages.
If You Shoot with Zoom Lenses...
Lenses with multiple focal lengths; e.g., 12-24mm/f4, 24-70mm/f2.8. Choose MPR-CL II. The MPR-CL II is 7.4-inches long (189mm) and weighs 6.8-ounces (194g). Because of the way internal focusing mechanisms work inside zoom lenses, their nodal points tend to be further forward by the front element (this is a generalization-your mileage may vary). This is why zoom lenses generally require a longer nodal slide. The MPR-CL II also has a built-in circular level and laser-engraved scales on both sides.
If You Shoot with non-Collared and Collared Lenses...
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Image above shows a camera body mounted on the 192 Precision Plus Package.
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Just rotate the mini-clamps, and now you can use your collared lens on the same slide.
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If you only need a clamp oriented for camera bodies, then our 192 FAS Package is ideal. Sliding lever-release clamp platform has lock knob and handy index marker for precision placement.
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Consider our 192 Precision Plus Package if you want to use your short lenses and your long lenses for shooting panos. The reason you need a different solution for this application is because the mounting dovetails on camera body plates run left/right, while the mounting dovetails on lens plates run fore/aft. Our 192 Precision Plus Package can handle both of these.
 Shown at left, our 192 Precision Plus Package includes:
- One MPR-192 rail
This flat rail is identical to the MPR-CL II but without the built-in clamp.
- Mini-Clamp Package
One B2-mAS clamp and one B2-FAB clamp mounted back-to-back. This sliding clamp platform can freely slide the length of the rail, and the mini-clamps can be rotated so that either camera bodies or collared telephoto lenses can be mounted. Very handy!
- The 192 Precision Plus Package weighs 11.6-ounces (330g).
If You Shoot with Fisheye Lenses...
These can be tricky because if the nodal slide is too long, then the nose end of the rail will appear in the image. The best way to determine the rail length you need is to set your camera on a table top very close to the edge. While looking through the viewfinder, slowly pull your camera away from the table edge until you no longer see the table in the image. Step back and measure the distance from film plane/digital sensor to the table edge. Most folks who shoot fisheyes tend to choose our 192 Precision Plus Package or our 192 FAS Package.
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