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Panorama Stitching

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Many digital cameras, even some budget-priced pocket compacts, have a feature known as "Panorama Stitching" mode. If you haven't experimented with it yet, it is designed to help with a particular type of photograph, or rather series of photographs, in which successive shots are taken as the camera is panned across a scene. After you take the first shot, the camera shows the edge of that shot superimposed on the monitor so you can match up the position of features in successive shots. The theory is that the subsequent series of pictures can be matched up automatically in an image editing program, producing a long continuous photo showing an entire panoramic scene. When it's done well the results can be breathtaking.

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If you have experimented with it, and with the photo stitching feature of your editing software, you've no doubt discovered that getting a satisfactory result is a lot harder than it looks, and that the finished picture if often bizarrely distorted, and exposures don't match up between shots. The problem is that shooting the initial series of pictures is a bit more complicated than simply pointing the camera and turning slightly. Here's how it's done.

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The first and most obvious tip for panoramic photography is to use a tripod, and preferably one with a "pan and tilt" type head, rather than a ball and socket. The best results are obtained when the successive photos line up perfectly, so find a good vantage spot with a wide and unobstructed view and set your tripod up nice and level. Check that when you pan the head from one side to another the camera is turning level with the horizon, and isn't tilted. It can take a few minutes to set this up, but it's worth it. You need to be able to rotate the camera freely in the horizontal axis without it moving in any other axis, so lock off the other pivots.

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If you're trying to fit an entire panorama into a single shot, it's normal to use the shortest focal length (widest zoom setting) that you have available. The greater the angle of view, the more of the landscape you can fit into the frame. However the large field of view of a wide angle lens has another effect; it also alters the angle of perspective. In single shots this is not immediately noticeable, since it looks fairly normal to our eyes, but if you compare two wide-angle shots taken from the same position but in slightly different directions you'll see that the perspective changes far more than is immediately obvious, and that the relative proportions of objects are very different from one shot to the next.

If you shoot your panorama stitching shots using a wide angle lens, this perspective distortion will make it almost impossible for the editing program to line up the successive shots. The shape of features, especially at the edges of the frame, will be so different that the image-recognition system that helps the program match up the photos will be unable to recognise details from one shot to the next.

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