y portion of the image. This is
sometimes useful, but as a general thing stopping the lens down is not
advisable, as interfering with one's judgment in calculating exposures for
various negatives. Having secured the image correct in size and focus,
place thumb-tacks at all four sides of the sheet of paper or card used to
focus the image. These will serve as a guide to the placing of the
sensitive paper. Adjust the lens stop as desired and cap the lens, leaving
the room totally dark save for such safe light as we may have for working.
Place the bromide paper on the screen, using the thumb-tacks as a guide to
the correct position in this.

In making his first enlargements, the beginner should avail himself of the
help of test-strips. These should be about one inch wide and the length of
the paper. The exposure depends on a number of factors, among which are
light, negative, focal length of lens, size of enlargement, stops,
sensitiveness of paper, developer, temperature of developer, and length of
development. The first experiment had best, therefore, be made on a purely
arbitrary basis, for which we will take ten seconds.

Pinning a test-strip on the screen, we uncap the lens and with a piece of
cardboard shade two-thirds of the strip during five seconds; move the
cardboard, and give the next section five seconds making ten for the
first; then remove the cardboard entirely and give five seconds more,
making fifteen for the first, ten for the second, and five for the third.
Now develop the strip. If the fifteen seconds portion finishes development
in less than one minute, and the ten takes approximately a minute, we will
know that our basis was correct. But if all three were over-exposed or
under-exposed, as shown by one minute's development, we can expose the
next test-strip accordingly.

In determining the correct exposure, the method already set forth for
contact exposures is a reasonably good one. If the paper with a given
exposure takes half the proper time to develop, halve the next exposure;
if double the time, or more, double it. More could be said on the subject
of exposure, and possibly to advantage; for instance, there are tables
showing the exact relation of exposure to the number of times of
enlargement, but complicated calculations in the dark-room are troublesome
and a test-strip is simpler. After a while one gets the ability to
determine the approximate exposure required by looking at the enlarged
image o