Of Panoramas and Polarizers
Blog Entry: November 9, 2010
This week we bring you a bird’s eye (sort of…) view of Whitman Mission from the highest point in the park.
This is a panorama of four separate images (taken a few weeks ago while the leaves were still changing) that I then stitched together in a photo editing program to produce a seamless image. Most digital cameras sold nowadays contain a suite of software that includes a program to stitch together multiple images to form panoramas, so this is something that almost anyone should be able to do regardless of what kind of camera you have.
Some important things to keep in mind when taking photos that you intend to merge into a panorama: First, be careful to keep the camera at the same level from shot to shot, otherwise you'll end up with something looking like a jigsaw puzzle in the end. Second, each individual picture needs to have roughly the same level of brightness. This may mean adjusting the exposure on your camera manually if portions of your scene are significantly darker or brighter than everything else. Photo-editing applications do a relatively good job at making small corrections in brightness when merging photos together, but if you have one photo that is brighter or darker by more than one or two aperture stops you will end up with a finished panorama that just looks plain weird. Finally, make sure you have plenty of overlap between images. I can tell you from experience that there's nothing worse than taking a series of pictures for a panorama and then getting home to discover that you accidentally skipped a small section of the scene. I normally play it extra safe and shoot for an overlap of at least 30% from image to image, if not more.
Finally, in the above panorama, I have committed one of the cardinal sins of panorama photography: if you're shooting a scene that includes large portions of blue sky, NEVER use a polarizing filter. Notice how the sky is bluer in the center and then progressively becomes more whitish towards the edges? That's the effect of a polarizer. Personally, I'm a big fan of polarizing filters. They're one of the cheapest filters you can buy and great for landscape photography since they darken the sky and increase both contrast and intensity of colors on a sunny day. However, the extent to which they do this depends entirely on the angle between you and the Sun. Polarizing filters are most effective at 90˚ east or west of the Sun, while they do almost nothing for you if you are looking directly into or opposite the sun. South (and therefore the Sun) is to the left in this image. Notice how the polarizer has its greatest effect on the blue sky at 90˚ from the Sun and therefore the sky is bluest to the west, which is in the center of the image. In a single image the field of view is normally not large enough for this change to be noticeable (unless you're using an ultra wide angle lens), but when you have a nearly 180˚ panorama, like the one above, you end up with a rather unnatural looking sky.