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Shooting Photos for Panoramas
- — 25 July, 2006 15:28
As surely as ice cream is tasty and parents will never understand their kids' music, panoramic photos are cool. Long ago, panoramas required special cameras, film, and lenses--and were often literally stitched together from a series of prints. Today, anyone can make a professional-looking panorama with a digital camera and inexpensive software that does the "stitching" automatically, blending the edges of adjoining images in such a way that the result is virtually seamless.
In this Here's How, we'll take a look at panoramas and see how to take better panoramas by better preparing the original images that will be stitched together.
Shoot Straight and Level
The best panoramas start out with good individual images. One way to ensure that your photos will stitch well is to shoot them all straight and level. The camera's lens should be level with the ground beneath you and the camera can't be tilted; the horizon must be level in the viewfinder. If each shot is straight and level, then your computer's stitching software will have a much easier time matching elements in the pictures and there will be less blending and approximating necessary to complete the panorama.
You can do this by eye, or you can attach a level to your camera. If your camera has a shoe for an external flash, for instance, you can get an inexpensive bubble level at your local camera shop and slide it into place on the top of your camera.
Watch Your Exposure
When you're shooting a panoramic scene, exposure can be a tricky thing. If you let the camera shoot each frame with automatic exposure, the exposure can vary wildly from one part of the panorama to another; you can see obvious problems in the finished photo, such as ink-black shadows that quickly evolve into light shade just a few feet away.
Here's what you can do instead: Look through the viewfinder and swing it around the region you plan to shoot, watching the camera's recommended exposure settings change. Look for the midpoint between the two extremes of exposure (such as the midpoint between f/5.6 and f/16) and use the camera's exposure lock button to lock this in. Use that exposure to take all the pictures in your panoramic series. Some pictures will be slightly underexposed, while others will be a bit overexposed. But there won't be any dramatic differences in exposure, and that's what's important when the panorama is stitched together.
Beware of Parallax
Parallax is an optical illusion in which things near to us appear to move faster than things farther away. When you're shooting a panorama, parallax is a problem because, as you take a series of photos and turn slightly to capture the next part of the scene, objects near to the lens will appear to shift with relation to objects in the background. Check out my panorama of an indoor scene. It looks like I've captured ghost furniture. What's going on here? A close-up reveals this detail.
Even though I haven't moved, but only rotated the camera, the post and chair appear to have moved left-to-right compared to the background. That's parallax, and I don't know any way to avoid it. The lesson here is that the best panoramas don't have prominent objects in the foreground. Try to capture scenes with a uniform, distant vista.
Panoramas Are Curvy
Finally, remember that what panorama software really does is turn a series of photos taken with a normal lens into a virtual wide-angle photo. Panoramas can look as if you shot the scene with a fish-eye lens. That means long, straight elements that are near the camera (like roads) tend to curve and bend. Check out my photo of a house with a long driveway.
Believe it or not, the driveway is quite straight in real life. The closer you are to those kind of subjects, the curvier they'll look. That's another reason to back up, or you can risk disorienting your viewer.
Watch the Focal Length
Does it matter what focal length you use when you take a panorama? Yes, it can. Most panoramic stitching software is designed to accommodate a wide range of focal lengths, but the reality is that these programs do best, in my experience, if you stay away from the wide-angle end of your camera's zoom.
The problem with wide-angle shots is that they have a tendency to warp the edges of the picture. Like a fish-eye lens, the wide-angle mode distorts the view. And that makes it harder for your software to successfully stitch overlapping scenes together. The end result is overlapping ghost images, reminiscent of the parallax syndrome I demonstrated.
Here's what it can look like when you try to stitch together a scene shot with a camera set to about 20mm; I've used two shots that were stitched together approximately in the middle of the panorama.
Take a look at a detail in the scene, and you see where the software got confused trying to combine the various wide-angle images. Aside from the obvious blurring, some doubling is apparent in the downward-hanging branches to the right of the tree trunk.
Don't Neglect the Edges
When you create a panoramic photo, your computer is essentially manufacturing a wide-angle image from a series of photos. And that means the edges of the resulting panorama will, by necessity, curve in a way that makes it hard to crop the photo into a nice, even rectangle unless you discard the edges. In addition, you'll get variations in the top and bottom edges of your photos as the framing varies slightly from one shot to the next. And the more photos you include, the more pronounced the effect becomes. You should take all this into consideration when you shoot the pictures, or else the resulting panorama can be very tricky to crop properly.
Consider this simple three-photo panorama. It's pretty easy to crop, because there's only a little curvature at the edges.
But my next panorama is composed of ten individual shots, in two rows. You can see that the curvature is quite pronounced.
Keep this in mind and always shoot more of the scene than you think you'll want in the final panorama. By over-shooting, you'll be able to get a better (or perhaps more complete) final image.