Dr. W. Henner Fahrenbach
"Patterson-Gimlin Film Resolution"
In view of the renewed vigor that the Patterson movie frames are being examined, I will repost this discussion on resolution (with verifying recalculation and minimal changes) that went out about a year ago.
The resolution of a film, as stated in Kodak handbooks, is determined under laboratory conditions, as for example on an optical bench, by photographing a black and white grating pattern, meaning 100% contrast modulation, onto the film. If one uses a grating whose spacing gets tighter and tighter, there is a point at which the adjacent lines smear into one another and can no longer be separated. That is the stated resolving power of the film. This resolving power cannot, of course, be realized under photographic field conditions, since A) the camera isn't mounted on a solid pier; B) more importantly, real life scenery does not have close to 100% contrast of closely adjacent objects, and C) transfer of the available contrast from scenery to film (modulation transfer) occurs in an imperfect fashion. However, contrast contributes in an important manner to the smallest detail that can be detected in the final print. Additionally, any part of the intervening optical system, for example the camera lens, the enlarger condenser (if any), the enlarger lens and the coherence of the enlarger light source affect the resolution of the final image and will always degrade it from the optimum stated for the film. Multiple serial reproductions exacerbate these problems substantially.The emulsion that was used by Patterson was, as far as is known, Kodachrome II. That film has a stated resolving power of 63 lines/ mm. In addition, Nyquists's Sampling Theorem states in its simplest fashion, that for a signal (minimal image element) to be detected, you need in effect the space of two lines, which brings the resolving power to 31.5 lines / mm. Stated differently, the smallest interval that can reliably resolved (under optimal conditions) in this film is (1 mm =1,000µm) divided by 31.5 lines = 31.7 micrometers or microns on the film. This is the physically limiting value for Kodachrome II, below which you may see assorted patterns that are part of the emulsion, but that carry NO image information and are, by definition, background noise. Advanced image manipulation techniques can modify contrast, edge sharpness and other aspect of the image, but cannot generate signal from noise and put the interpretation at risk.It will be apparent at this point that all this calculation can be done without reference to an actual picture. One is dealing, after all, with a plain physical process that is well understood and for which the pertinent literature is voluminous.The stated resolving power pertains to the original negative. To find what this value of 31.7 microns corresponds to in the prints in circulation, one has to know the magnification. When one does crucially important enlargements, one should print a transparent millimeter grating directly at the same settings
as the original negative, whereby one generates a reference of the magnification. Since this is not available, one has to extrapolate stepwise from the size of an original 16 mm frame (at 1x) and scale it up to the larger images, a process that accumulates errors but still provides a good "ballpark" figure.A good starting point is provided by the images in Perez' "Bigfoot at Bluff Creek" (1992; BigfooTimes; D. Perez; private printing. 10926 Milano Ave., Norwalk, CA 90650) He shows a one-to-one contact print of a bit of 16 mm film for calibration and a slightly larger image, which includes the frame, at 11.3x. Beyond that point it becomes necessary to find crisp fiduciary marks in overlapping pictures of different magnifications to extrapolate further. Thus, the Dahinden commercial picture of the full frame No. 352 (wide format) is approximately 37.5 x, the Dahinden vertical pictures of Frames 323 and 352 are magnified about 133 times, and the Halpin and Ames pictures are about 110 X (Manlike Monsters on Trial, University of British Columbia Press, 1980).Some pictures that have been circulated of Patty's head alone can be calibrated by the preceding pictures and have been found to exceed 1,000 fold magnification. For the Patty rear view pictures, information available from NASI indicates that the large Dahinden pictures are at exactly a third of the magnification of the sideviews, i.e., 44 times, the Halpin and Ames picture 22 X. If one multiplies the maximal possible resolution that this film allows with the magnification, one arrives at a value that constitutes the absolute smallest resolvable detail in the pertinent print. This value will inevitably be overly optimistic (too small) because one is not dealing with a stark black-and-white image nor a steady camera. For the vertical images (Frame 323 and 352) this value is (133 x 31.7 microns) = 4,216 microns, or 4.2 mm. Cut out a paper circle with this diameter and it will approximate the smallest detail (optimistically) resolvable, slightly over 2 inches on Patty's body. (Actual resolution, for the above-mentioned cautionary reasons is apt to be worse than that, possibly by half)
Analysis based on anything other than direct copies of the original film frames is also to be avoided at all cost due to the above considerations.
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