Appreciation through Understanding
stars move in circles around Polaris in your camera? As the lawyers say, it depends. If you have the usual rectilinear lens
(anything other than a fisheye lens); and your camera is not pointed directly
at Polaris, the answer is no. With a
slight tilt away from Polaris, the star trails become ellipses and more extreme
tilts produce parabolic or hyperbolic paths. Of course, all the star trails are beautiful, so why does one care about
mathematical descriptions of their shapes? The answer is that photographers need to calculate maximum exposure
times that will still avoid noticeable star trails resulting from motion. The rate of growth of trails for stars with
various declinations and positions on the sensor is the subject of this study. It has been prompted by the approximate
equations1 and inaccurate calculators2 that have been
posted online. Here I will display exact
calculations of star trails that can serve as bench marks for approximations
and rules of thumb for photographers. For the complete article see Luminous-Landscape.
This is just one entry in the weblog Photophys.com: The Science of Photography. You may want to visit the main page of the weblog
Below are the most recent entries in the category General, some may be related to this entry.