We ran across this piece in Fortean Times online, reporting on some experimentation a British researcher did on orbs with a stereo camera.
In findings presented at the conference of the Society for Psychical Research in
September 2010, and published in the November 2010 edition of Anomaly,
Steve Parsons reports the results of his exhaustive experiments using a Fujifilm
W1 3D digital camera, whereby matched stereo images are taken of the same view.
A total of 1,870 stereo pairs of images were taken at over 20 locations in the
UK and Eire, including a number of allegedly haunted sites. Some 630 orb-like
images were obtained. If orbs are not reflections of particles less than 2–3cm
(roughly an inch) from the lens, then the orb should appear in both images. In
491 pairs obtained, the orb was only present on one image, and in 139 pictures
orbs were present on both images, but not in a position that corresponded to the
individual orb being the same object.
As we indicated on our Q&A page, we do not dismiss the presence of orbs as being paranormal manifestations completely. If an orb is seen visually in real time, or can be shown to cast its own light (or shadow), or is very tightly correlated to another piece of evidence, or is captured without flash, or is captured in the same place by two different cameras…it may well be a genuine paranormal anomaly.
True believers in orbs as paranormal manifestations will undoubtedly remain undaunted by this research, and for us, that’s fine. This field requires each investigator to use their own rules regarding what counts as evidence. In our methodology, we seldom pay much attention to them.