Since I do a lot of panorama work, I get a lot of questions about how to create them. The answers are both obvious (you take a bunch of overlapping images and software figures out the final image) and unobvious (geometrical, physical, and lens issues intrude), so it's easy to get tripped up. Today I'm going to just address the "capture" side of panoramas.
Over time, we've developed a pretty large array of ways to get a sequence of overlapping image data. I'll tackle these from simplest to most advanced:
- Casual. Just take overlapping pictures! You can do this with any camera in any situation, but it works best with compact cameras and subjects that are more distant from you. The trick is to make sure there's enough overlap. It's better to have more overlap than less.
- Casual crop. The camera just visually crops out top and bottom of the frame to create the impression of a pano. But you lose a lot of pixels this way, so it's not for large pano prints.
- Casual plus help. Many compact cameras have "pano helper" modes, where they suggest the overlap you should make for each picture by putting a ghost of part of the previous image over the LCD as you're lining up the next image. You don't have to be absolutely precise in lining things up, but this takes care of the "how much overlap" question.
- Casual spin. Fujifilm and Sony both have higher-end compact and/or mirrorless cameras that create a panoramic image from a continuous slow pan. The downside is that getting the timing of the pan down takes practice and the resulting image doesn't take in the full resolution of the camera (to give the internal software some leeway with the casualness of the data).
- Aligned rotation. Here you set up the camera and lens to rotate around the center of the optical path. This means you have to find that center first, then use the proper equipment to place the alignment at the center of your rotation (e.g. tripod). The reason why "alignment" is in all these advanced capture modes is due a problem called parallax, which I'll get to in a bit. But we're back to the "make sure there's enough overlap" problem.
- Aligned shift. Using a shift lens, you keep the front of the lens stationary, and shift the camera back to achieve the overlapping images.
- Aligned rotation in rows. Here you not only rotate on the horizontal axis (to get the width of the pano) but you do multiple rows that are rotated on the vertical axis (to get the height of the pano). The overlap problem is now extended in both axes: you need to overlap horizontally and vertically.
- Motorized aligned rotation. A number of motorized rotation mechanisms have appeared, the most common of which is the GigaPan. Once set up, you enter the lens and sensor parameters and all the rotations and overlap is handled automatically.
Hmm, doesn't seem so simple once we get past the casual methods, does it? Unfortunately, it gets worse.
Even the casual methods have the problem of parallax in them. It's not quite the same kind of parallax, but here's how to see what parallax is: hold your finger up in front of your face and align it with a distant object. Now close one eye at a time. As you move between eyes notice how the alignment changes between your finger and the distant object.
The same thing happens to light rays in a lens. I'm going to grossly simplify here. Remember, the classic thing is that lenses reverse the world, kind of like this: 7 >< L. A light ray at the top crosses over to become the bottom, one at the bottom crosses over to become the top. Well, if you rotate right at the point where the light rays are crossing, everything aligns properly between near and far. Rotate at any other point and parallax starts to sneak in.
Compact cameras make decent casual panorama devices because the lens to sensor distances are so small that even casual rotation means you're rotating probably close to the no-parallax point (on a tripod, less so handheld). Moreover, most people usually casual methods aren't standing close to the nearest object when doing a pano, so parallax isn't a huge issue to start with. But stick a full frame DSLR with a wide angle lens in the classic landscape scenic position of being close to a near object (to achieve visual depth via perspective) and try a pano and you'll get massive parallax issues that make the resulting images unstitchable.
That's why we go to the aligned rotation techniques for serious DSLR work. So we have two things to deal with: how to find the rotation point, and how to do the rotation.
Since we need a good rotation rig to even made use of the right rotation point, let's deal with that first:
- Level base. If you've ever stitched an un-level sequence, you'll immediately recognize that this is our number one requirement. Without a level base we're not going to have a result that fits in a rectangle, it'll instead need a diagonal parallelogram frame ;~). The simplest solution here is to use a tripod with a leveling base. Done. You can do it with any tripod and some bubble levels, but if you watch me set up with a leveling base while you struggle with leg positioning to get a level base, you'll switch. It's a couple of seconds of setup versus many seconds, perhaps minutes. If I ruled the tripod world, no tripods would have centerposts and all would have leveling bases. (Okay, that's a bit of a stretch: sometimes centerposts are useful.)
- Rotation base. You can use the rotational base of a ballhead, but that means that you need to get the top platform on the head level, too. Doh! Better to just stick something like a Really Right Stuff PCL-1 on the tripod itself to do the basic horizontal rotation. Since you leveled the base, voila, a PCL-1 will do level rotation.
- Positioning plate. You're going to need something that you mount the camera to that allows you to move the position of the lens so that the rotation point we'll eventually set is exactly above the center of the rotation of the base. In Really Right Stuff's cryptic jargon, that's something like an MPR-CL (there are many ways to do this particular offset though--I sometimes use a focus rail). If all you're doing are basic horizontal panos, this and the previous two things (and some people cheat by using their tripod and head for the first two at the expense of setup time) are all you need. Really Right Stuff sells the last two as the "Pano Elements Package."
- Vertical rotation setup. If you're going to capture rows of aligned images, you need more, and it gets complicated enough here that I'll just point you at Really Right Stuff's explanation and their Omni-Pivot packages.
Plenty of other options exist for setting up aligned panoramas. I've already mentioned the automated GigaPan, and if you're doing things manually Novoflex and others also make competent bases and plates. As I noted earlier, I sometimes use a focusing rail as a plate, as having things that have multiple purposes cuts down on the number of things you're carrying and the weight.
So, how do we find that no parallax point? Assuming you've got your base leveled, you do the same thing as we did with our fingers, earlier: sight a near and distant object, align them at the center of the frame, and rotate slowly while looking through the viewfinder. Good near objects are things like a pole or narrow tree trunk. If the near object moves relative to the distant object as you rotate, you're not at the right point. Keep moving the camera/lens forward/backward until you find the point where the near object stays fixed to the distant one. Now lock everything down. Some of us go so far as to engrave our plates with our favorite lens positions so we can just align everything via marks.
When taking the sequence of images to make the final panorama:
- Lock down. Manual white balance, manual focus, manual exposure (usually based upon the brightest portion of the overall scene), and make sure you're not using any Picture Controls that have an "Auto" setting in them.
- Overlap. The wider the lens used the more you should overlap. 25-33% overlap is usually enough.