STEREO PROCESSING 309guides, such as the Taxiphot, presents quite a problem in rebuild-
ing, while the Mattey, with its loading weight resting on top of
the slide, and already adaptable to 6x13 or 45x107, requires only
shortening of the trays, For glass mounted 35mm slides, color trays
are used (1 2 slides to the tray) and for rigid cardboard the normal
25 slide trays are used. The semi flexible “folder” type of card-
board mount is not rigid enough for either projection or auto-
matic viewer use.
The same thing is true of film positives made from the older
negatives. The film is usually unmounted and is too flexible for
anything but the hand viewer. If glass mounted, the slide is too
thick for anything but color trays in the cabinet. There have
been some successful experiments in the use of thin plastic for
binding, but for projection it must be remembered that some
plastics are optically active and produce rainbows over the screen.
If slides are to be projected it will be necessary to use some plas-
tic material which is inactive. The acrylics are satisfactory, but
the cellulose plastics are, as a rule, very active.
We shall of course ignore the 35mm color positive as it is proc-
essed for you.
Paper Prints.-There is nothing out of the ordinary in making
the paper print other than the problem of keeping the tonal range
within the range of the paper with no burned out highlights or
coal black shadow areas.
The short tonal range of paper prevents the full tonal repro-
duction of the original and hence tends to diminish the degree of
stereo relief and produce stereograms in which round objects pre-
sent a decidedly flattened appearance. Human figures resemble
“gingerbread men.” This defect is less noticeable when soft, full
range prints are made and increases as the print becomes harsh
in contrast.
Masking.-Prints may be masked as you choose, but the film
negatives should be carefully spaced when transposing. The usual
3x6 steseogram has no space between the units, but it is sug-
gested that the amateur slit adhesive tape to a 1/8” width and
leave this much space. The mask should be cut with a 3/16” bar
between opening so that any slight irregularities of the I/gN tape
can be obliterated.
Prints 6x13 and larger appear best with rectangular masks hav-