|Most users of condenser enlargers
give little thought to the lamphouse beyond occasionally changing
the lamp and perhaps cleaning the dust off the condenser lenses. In
fact, the condenser enlarger is a precise optical projector.
The optical system must efficiently
project the light from the enlarging lamp evenly across the negative
and approximately focus the image created to the rear of the
enlarging lens. The design of the condenser lenses must take into
account the size and shape of the enlarging lamp, the size of the
negative, and the focal length of the enlarging lens with which they
are to be used. Although it is possible in limited circumstances to
use just a single condenser lens, only one Omega enlarger, the B635,
used this design.
Most Omega enlargers, and most
condenser enlargers in general, are based on the double condenser
system, which usually utilizes a pair of plano-convex (simply
meaning one side is flat and the other rounded) lenses mounted in a
housing which, in use, will rest on the negative carrier. Because
the light is focused to the enlarging lens, that single set of
condensers will work efficiently with only a limited range of focal
length lenses. For a 4"x5" enlarger with its standard condenser
set, that would be about 135mm to perhaps 160mm lenses. Attempts to
use the same condenser set with shorter focal length lenses will
result, as some users have discovered, in considerably reduced light
output and much smaller enlargements than they expect.
A variation on the double condenser
system is the reflex lamphouse in which the light is projected
horizontally through the first condenser, then is angled down off a
45° mirror or reflector to the second condenser.
In order to provide users with the
ability to use the same enlarger for smaller formats, the initial
approach was to provide accessory condenser sets. For the condenser
lamphouses fitted to the DII,
for example, there were three additional condenser sets available -
one for 90-105mm lenses, one for 75-80mm, and another for 50mm and
shorter focal lengths. The problem with this approach is that the
extra condenser sets are a significant expense, are somewhat clumsy
to change, and require cleaning and storage when not in use.
With that in mind, alternate
solutions were devised. Most involve the addition of a third
condenser lens. In general, the extra condenser is added to "prefocus"
the light from the lamp before it reaches the main condenser set.
How that third lens is used does vary. For medium format enlargers
like the B22, the third lens is most often a supplementary or
auxiliary condenser, added above the double condenser set when the
user is working with smaller formats. In the C67, the third lens
was inserted in place of the upper condenser of the standard pair.
The 6x9cm format B7/B8 condenser lamphouse had two supplementary
condensers - one used for 2¼"x2¼" negatives and the other for 35mm
and smaller formats.
Because 4"x5" enlargers must
accommodate even more negative sizes than medium format enlargers,
the approach is different again - the third lens becomes a
"variable" condenser. It is adjusted for different formats by
raising and lowering it relative to the main condenser set. With
the DV lamphouse, the user simply inserts the lens into different
slots provided in the lamphouse. The D6 Zoom lamphouse accomplished
the same thing, but used a mechanism to raise and lower the third
lens by means of an adjustment knob on the side of the lamphouse.
In both cases, however, the auxiliary lens must be removed when
working with 150mm lenses.
While the supplementary and variable
condenser solutions are not quite as efficient as specific condenser
sets, they do provide excellent performance at a more reasonable
cost and greater convenience.
Since different condenser lamphouses
have different designs, it's important for the user to understand
the design of the unit they have and ensure that they have the
accessories required so that lamphouse can be configured correctly
for the negative sizes and lenses to be used. It's even more
important for anyone about to purchase a used enlarger to be aware
of these requirements.