STEREOGRAF'HIC TECHNIQUE 95heavily into soft-focus stereogram making, with results which are
better imagined than seen.
But, all in all, the greater the sharpness of the stereogram in all
planes, the more satisfactory it will be.
Of course to produce this effect, inasmuch as the best stereo-
grams have some relatively nearby object and many of them in-
clude backgrounds at infinity, a small lens aperture must be used.
When possible, apertures of fii and f16 are advisable, but ex-
cept under the most intense light, this means exposures of such
length that the tripod is necessary.
There are many times when it is necessary to use larger aper-
tures, even to the extreme of f3.5. Then, too, the shorter the
focal length, the greater the aperture which can be used without
loss of too much depth of field. In short, the matter is one which
you should decide for yourself, but make a practice of referring
to depth of field tables (or to the depth scale on your camera if
it has one). Then use the smallest aperture which includes the
desired field. If you can cover the field at f8, there is little point
in stopping down to f16, and the quadruple exposure gained
aids a lot in balancing exposure against necessary shutter speed.
That matter of having an object relatively near is not a rule at
all, it is simply a reflection of normal conditions. It is not often
that you find yourself in a position where there is nothing before
your eyes for a distance of 100 feet or so. Upon a cliff edge or at
a window in a tall building perhaps, but such conditions are not
corn mon.
When you take a walk in the country, or in a large park, you
can see quite easily that details in the distance, say at 100 yards or
less, are not so sharply differentiated in spacing and relief as are
objects nearer at hand. Of course the size of the object enters into
this, but for ordinary objects, people for example, a distance of 15
or 20 feet reveals more contour than can be seen at a distance of
100 feet. It is just this fact that makes the 15 foot stereogram more
definite in relief than the one made at loo feet.
This of course leads straight into the question of the distance
limits, but this has been discussed elsewhere in this book. It is
enough to say here that thousands of amateurs who never heard
of the limits have made stereograms at 30 inches and have been