Wednesday, July 25, 2012

Panoramic Portrait Position

I've been reading up on various photo tricks in preparation of a trip I hope to take soon. I've become increasingly interested in panoramic photos. I recently learned about Microsoft ICE (used for stitching panoramas that were taken from a single stationary position) and Photosynth (which permits the photographer to take his viewers on a virtual tour in and around a location). Both are free and both require a bit of forethought.

Normal panoramas are 180-degrees or less and those teaching the subject usually recommend a tripod. One nice feature of ICE is that neither a tripod nor single camera orientation are required. However, other customary photo-stitching programs usually expect a single orientation and this is the subject of this post.

If you try to use a tripod and a portrait orientated shot, you will get more distortion because of the lens turning on an imaginary axis that accentuates the issue. After thinking about that issue, at first I thought a monopod might help, but I can neither afford any more equipment at this time nor do I want to carry anymore equipment. One particular video made me think of a solution that may help portrait panos. Although  that video addresses camera shake and not panoramic photos, it was all I needed.

On your typical tripod, the unit that the camera attaches typically swings up (for putting the camera in portrait framing). On the leg of the tripod that is closest to swung-up position, extend only that one leg to a height where the viewer will be at your eye level. Now imagine a line between the bottom of that one leg and the lens. Position the camera so that that line sets your vertical level. My Canon 7D has a electronic level that shows both vertical and horizontal leveling. Once you have a sense of your vertical level, and your lens is flat against that imaginary plane, you need only pivot on that one leg as you rotate to take each frame.

I learned some other things from another video regarding preparing for taking panoramic images. Here is a recap of those lessons:

Good Technique for Pano Prep

Hardware: Setup on tripod. If a zoom lens, set to mid range. (Reduces distortion).

  • Photographing in portrait position (camera turned sideways) can cause greater distortions in stitching, but has added benefit of greater breadth in image. (Untested, but more overlap may help here.). One aid is simply put an object on the ground as a reference point that you hold your lens over it and rotate with lens centered above it (which means hand-held photography instead of on tripod).

  • Note: The worries associated with panoramic photos are not relevant to Photosynth photography.

Plan: Determine ahead your pan start & end points

PreScan: Scan the "horizon" of your planned pan without taking a pic to ensure that everything you want in the pan will be visible.

Exposure Averaging: Take 2 or 3 test shots: Pan-Start, Mid, Pan-End and check histogram. As much as possible determine an average that will get the whole pan correctly exposed. Reason: You want Manual mode and manual focus so that the whole pan, when stitched, will appear evenly exposed as if it truly were a single image.

  • With Auto, Av or Tv, take your readings, determine best mid-point focus and from the test shots and set your focus and exposure.

  • Start with a small aperature (large number above 10). This will ensure more is in focus than is out of focus.

Manual: Finally, set to Manual mode & manual focus and proceed to take your pan shots, remembering to include adequate overlap in each image so that alignment in the stitching program will be easy.

  • Adequate overlap is up to 50%. It is not less than 25%.

Below is a portrait pan I took. In the photo I annotated the problem areas.

Here is a simple illustration to indicate the tilted tripod method I used. The grey dash-line indicates the imaginary vertical plane against which the lens and one leg of the tripod match to. The brown line is the one extended leg of the tripod, the blue is the camera and the red the part on the tripod that connects to the camera. I tried to illustrate that the camera was in portrait.

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