several methods of automatic dodging such as unsharp-mask technique, the infra-red 
inhibited-phosphor printer by Watson or one of the scanning spot printers such as 
that by Log Etronics or Cintel. 
The “meticulousness” of the control from point to point in the negative is deter- 
mined in the first two by the "sharpness" of the mask or of the inhibiting image, and 
in the last two by the size of the scanning spot. The degree of control is determined 
by the gamma of the mask, the strength of the infra-red inhibitor, or the amount of 
negative feed-back. 
For the ultimate reproduction of information in the positive, every resolvable spot 
in the negative must be feptoduced within the straight line portion of the positive’s 
curve. This procedure produces a “muddy” print as seen from one or more feet, but 
under adequate illumination and magnification it will yield all the information recorded 
in the negative. 
Both black and white are the end-points of complete fade-out of information and 
their feeble-toned *vicinities" must be avoided if detail rather than drama is required. 
Where a higher degree of relative tone-rendering of areas is desirable, lower 
gammas for the unsharp mask will reduce the correction as far as required. It should 
be possible to adjust the feed-back on the scanning spot printers similarly, and so make 
positives available, from the same negative, to suit the most particular interpreters. 
Transparencies on clear base, examined over a suitable light table, probably give 
the highest “signal-to-noise ratio” and therefore transmit the most information. Glazed 
glossy prints on textureless paper examined by transmitted light are nearly as good. 
The tone scale gets shorter by reflected light, and anything but a glossy surface “raises 
the noise level”. Speculor reflection, however, may cause trouble except under 
controlled lighting; and unglazed glossy prints are recommended for field use. 
Visual Aids 
The second group of factors affecting the interpretability of photographs is related 
to the problem of seeing what the photographs have recorded. (It is assumed that a 
stereoscopic pair is considered essential for photo interpretation.) 
What can your unaided eye see? Fiftieths of an inch, or half millimeters are 
getting small but you can do better than that; fifths of millimeters are difficult and 
perhaps unreliable except under good illumination. To see 10 lines per millimeter 
may be possible but will be hard work for the best of eyes. 
The photographs that have been discussed, made on Kodak Plus X film, exposed, 
processed, and printed as described, resolve between 20 and 30 lines per millimeter 
at a scale of 1:15840. It is obvious therefore that, for easy observing, good illumination, 
and magnification between 5 X and 10 X w ill be necessary. It will also become obvious 
that with such magnification the orientation of the photographs under the stereoscope 
becomes increasingly critical. 
Some suggestions are offered. 
The first is primarily for use in the field where pocket stereoscopes (or f flexible 
eyes) are the only available equipment. 
Multiple stereo prints comprise three printings on one normal-sized photograph. 
The centre half is printed from the centre of three successive negatives, and the outside 
quarters bear the conjugate images from the adjacent negatives, like two adjoining 
stereograms 9 in. tall. They are printed with the aid of masks designed, not only to 
control the eye base and print spacing, but also to compensate for crab angles. They 
can be viewed directly—the base being 64 mm—or with a 2-power or 7-power lens 
stereoscope. Figs. 2a and 2b show two such multiple prints. 
5 
Fig. 2a