Solving the Panorama Parallax Problem
November 14, 2016
I hate spending money on camera gear. I particularly hate it when I buy something I think I really need, and it turns out I only use it rarely. So I’m always looking for ways to create the images I envision without spending still more money.
Take panoramas, for example. Does shooting high-quality panoramas require purchasing specialized panorama hardware? The answer is sometimes yes, sometimes no. Let me explain.
Setting up a panorama of a distant subject requires just two steps. First, adjust the length of the tripod legs to level the base of the tripod head, which is the plane of rotation as you pan the camera left to right. Second, level the camera itself from left-to-right so horizontal lines are horizontal. Put all camera controls on manual (manual focus, manual exposure, etc.). Pan the camera to the first camera position and shoot a frame. Pan to the next camera position, being sure the two frames overlap by about 30 percent, shoot the next frame, and continue. You don’t need a special panorama head for your tripod.
Of course, the best panoramas, like most good landscapes, usually have some kind of close-in foreground. Now you have an issue: parallax. To understand parallax, hold one finger up in front of your face, close one eye, and rotate your head left to right. You’ll see your finger move in relation to the background. That’s parallax. It occurs because your eye is not centered on the axis of rotation of your head. Examine figures 1 and 2 below, which show what happens when you shoot the components for a two-frame panorama with a 16mm lens about three feet from the foreground, without correcting for parallax. Notice how the tripod and light stand don’t line up in front of the same part of the background. For example, the light stand aligns with the front entryway of the distant house in figure 1 but is well to the left of the entryway in figure 2. You’ve just thrown your stitching software a wicked curve ball. Where should it put the light stand in relation to the background?
The best way to correct for parallax is to buy a nodal slide, shown in figure 3. This allows you to slide the camera back so that the lens’ nodal point, the “eye” of the camera/lens system, is centered over the axis of rotation of the tripod head. (The panning clamp shown in the figure allows you to level the plane of rotation by adjusting the ballhead rather than adjusting the length of the tripod legs. This additional purchase will save you much time and frustration.) However, this is an article about how you can create more images without buying more stuff. As I mentioned at the beginning, you only need to worry about parallax when your foreground is close to the lens. But how close is too close? I ran an experiment to find out.
First, I used Lightroom CC to stitch the two images shown in figures 1 and 2 and got the comic result shown in figure 4. Obviously, three feet is much too close. I continued shooting two-frame panoramas at increasing distances from my foreground using 16mm, 24mm, and 35mm lenses. The greater the distance between the camera and the foreground, the fewer stitching errors I encountered. Stitching errors were rare at 50 feet, with only one bad stitch in six trials. I had to go all the way out to 100 feet, however, to achieve perfect success in every trial.
At every workshop I teach, some student will proudly describe how they banged out a hand-held panorama and the software successfully stitched it together. My response is always, “I’m so glad you didn’t blow the opportunity of a lifetime by using sloppy technique!” For me, the bottom line is this: if an opportunity to shoot a panorama presents itself unexpectedly, and I don’t have my panorama gear, I’ll avoid a composition that includes a close-in foreground, shoot the panorama, and hope for the best. But whenever possible, I’ll dig out the panorama gear and do the job right.
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