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RESOLUTION ISSUES IN SCIENTIFIC PHOTOGRAPHY Original Film vs. Projection Dupes
Prof. John Hart Program in Atmospheric and Oceanic Sciences University of Colorado Boulder, CO 80302 February 2002 nimbus.colorado.edu/hart/science.htm
Scientists often use duplicate slides of original material in lectures, talks, conferences, etc. How good are commercial slide duplicates, or "dupes". Slide projection causes film to fade quite quickly. Estimated lifetime (before significant fade) is 3 hours (in the projector) for Fuji slides and 1 hour for Kodachrome. When slides are projected often (as in a continuously running museum display, for example), use of "projection dupes" has been recommended. Fuji Slide Duplicating Film, CDU Type 2, reproduces the colors, saturation and dynamic range of Fuji film remarkably well! Projection Dupes cost about $1 each. More expensive dupes can be made (about $5 to $10 each for "reproduction grade"). These tweak the color and exposure and are generally done with a little more care by the operator. We simply took a Fuji Provia 100F slide of a resolution test chart and had a projection dupe made out of it. Below are the results.
Figure 1. Microscope view of the central test pattern of the original, using 35mm Fuji Provia 100F and prime lens optics at f11.
Figure 2. Blowup of the central portion of figure 1 (increasing the microscope objective from 1X to 10X). Block col 1 row 3, maybe row 4, is just resolved (IMHO). Half way between corresponds to about 77 lines per millimeter on the film, or 2750 lines across the film. Note the relatively small grain density.
Figure 3. Fuji CDU duping film, shot as a "projection dupe" of the slide used above. Note the much more profuse grain. (Microscope image using 4X objective, cropped to show this resolution block).
Figure 4. Magnified view of the ProjectionDupe's reproduction of the central block. To be about equally generous w.r.t. figure 2, 0/1 is resolved (0/2 in a stretch). 0/1 is about 1000 line pairs across the image or 28 lines per mm on the film. The film resolved at least col 1 row 3, which is obviously long gonzo in this test.
Figure 5. A Reproduction Grade ($10 each) dupe. Grain etc. is about the same as figure 3. This one is a little sharper. I attribute this to operator action, as the film, duping equipment, and processing are the same as in figure 3.
Figure 6. The Repro Dupe resolves about row 0 col 3 (IMHO, to same degree as figure 2). This is equivalent to 1300 lines across the film or about 40 lpmm on the film. Conclusions: Dupes using Fuji CDU do a great job at capturing color and density changes in Velvia or Provia slides (not shown here, but trust me, it is so). However, about 50 - 60% of the original fine detail is lost (77 to 28 - 40 lpm). While dupes thus may be desirable for projection, the resolution reaches the point where one might want to consider the truly archival medium: digital projection (see Film vs. CP5000 and Projector Light Output). | ||||||||||||||||||
