Page 106 - The Wellington photographic handbook

The condenser is an important part of an enlarging lantern.
It bends aside the rays of light so that they pass through the nega-
tive and also through the lens. A large condenser is a very heavy
and costly thing and this limits the use of the enlarging lantern
to relatively small size negatives. It is only for quarter-plate
or 5x4 negatives that it enjoys any great popularity, though
there are, of course, half-plate and whole-plate lanterns in use.
For quarter-plates the lantern is as convenient a form of apparatus
as can be desired. A form of lantern is made in which instead of
a condenser behind the negative there is a reflector illuminated by
one or two incandescent gas lamps so fixed that no light from them
strikes directly on the negative. This apparatus works very well, but
exposures are much longer than when a condenser is used.
The illuminant may be an oil lamp, an incandescent mantle,
acetylene, electricity or the limelight. Any of these will be found
suitable, and the choice is simply a matter of convenience, and
should have no great effect on the quality of the enlargement.
Properly managed, any one of these will give just as good results
as any other. Perhaps the most convenient forms for the amateur
are incandescent gas where gas is available, and a mantle and
spirit burner where it is not.
The action of the condenser is to bend aside the rays of light,
so that after passing through the negative they all pass through
the lens, generally more or less through the middle of the lens.
Consequently it may happen that the lens can be stopped down
without cutting off any of the light passing through it. This is an
important point for the enlarger to remember, namely, that when
a condenser is used the effect of stopping down no longer follows
the rules that apply when using the camera in the ordinary way.
If the stop is altered, there is only one satisfactory way of ascertain-
ing its effect upon exposure, and that is by a trial exposure.
In setting up an enlarging lantern for work, the first thing
to be done after lighting up, is to put the negative in position and
settle the size of the picture on the easel. This decides the position
of the different parts, and it is only a waste of time to attend to
the even illumination of the picture before this has been done.
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