Page 103 - The Wellington photographic handbook

We multiply 192 by 192, getting 36,864, and 150 by 150,
getting 22,500. Then we know that the exposure under the new
conditions bears the same relationship to the exposure under the
old conditions that 22,500 does to 36,864. We can ignore all the
hundreds and deal with the thousands only. So the relative
exposures are 22,000 and 36,000, or 22 and 36, or 1 1 and 18. Multi-
plying the three and a half minutes by eleven and dividing by
eighteen, we get 2 minutes 8 seconds, which would be the exposure
under the new conditions.

It is well to understand how to make these calculations, as
they are all merely a matter of simple arithmetic, and if they take
a minute or so to do, at least save the cost of the piece of bromide
paper which would be wasted in the attempt to find out the proper
exposure. Those who do not care to follow this course must
make a trial exposure.

Before leaving this part of the subject, it should be pointed
out that it is most important to ensure the easel being square with
the negative, as otherwise the picture will be distorted.

If the lens used is that with which the original negative was
taken, it will give a satisfactory enlargement to any size that
may be required ; if not, the lens must be one that is at least capable,
in the ordinary way, of covering a plate the size of the original
negative right up to the corners.

FIXED FOCUS DAYLIGHT ENLARGERS.
There is another method of daylight enlarging, in which a
special enlarging apparatus is employed. This may be adjustable
to take negatives of different sizes, and to make enlargements of
different sizes, but the form usually met with is not adjustable,
but is a fixed-focus arrangement, in section similar to the sketch
shown below.
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