Canon Camera Hackers Manual page 207

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C H A P T E R 6 Advanced Techniques
Precise turning can be achieved with a nodal point adapter mounted
between tripod and camera. If you want to do multi-row work (for
spherical panoramas), you need a VR head. Several manufacturers offer
such devices; some of them are even motorized. If you use one of these
devices, you must determine the nodal point of your camera at the focal
length that you're using (because the nodal point moves when zoom-
ing).
To do so, first mount the camera on the nodal point adapter and the
tripod. The adapter allows you to shift the camera forwards and back-
wards. Set up the camera and tripod so that you have both a far and a
near object in the viewfinder. When you turn the camera, the distance
on the screen between both objects must not change. To judge this
distance precisely, you can make a picture and magnify it using the
zoom rocker in replay mode. Should the distance between the two ob-
jects change while turning the camera, shift the camera forwards or
backwards until you find the optimal position. Mark this position for
the next time.
Zoom level and focus should be left unchanged for all exposures. For
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landscape panoramas, setting the camera to infinity is fine in most
cases. Otherwise, you need to use the Override functions (section 4.3.1)
to dial in a fixed subject distance. A varying subject distance like that
caused by the autofocus system would make it difficult for the stitching
program to join the single exposures.
Exposure is often a problem with panoramas, especially on a bright day.
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The contrasts can be very high because you cover a large area. Some
photographers use a manually set exposure and keep it constant
through all of the images. In most cases, this will result in overexposed
and underexposed areas. If you want to work in this way, make sure
that you get the highlights right and let the shadows drown.
Personally, I would rather use automatic exposure for each picture
so that the camera can adapt to different lighting conditions. Modern
stitching software can detect these differences (it reads the exposure
data from the EXIF data) and blend the images seamlessly together.
Especially with high-contrast scenes, the results are usually better.
Some stitching software is even able to store the panorama in the form
of a HDR file to keep the full contrast range for later tone mapping (sec-
tion 4.6.2).
What you should do, however, is use the same ISO value for all im-
ages. This will give you a uniform noise level over the whole panorama.
Do not use automatic white balance but rather set the camera to a
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fixed color temperature, e.g., to Daylight or Cloudy.
When turning the camera, allow for sufficient overlapping between the
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single images. About one third of each image should overlap with the
previous image. The CHDK offers a great tool to register the single