CLOSE-UP STEREOGRAPHY 259fortunate that really capable instruments are so rare and so costly,
but many amateurs have done excellent work with only the usual
laboratory microscope. However, it is a serious error to try to
start with an instrument which has no condenser, and if at all
possible the condenser should be achromatic. For the benefit of
photographers who are inclined to laugh at “achromats” we will
add that the achromatic condenser is the finest made. It is desir-
able, but not so essential, that the objectives be apochromatic. In
any event, obtain the very best instrument which is possible.
In closing we should like once more to remind the beginner to
learn how to use the condenser. It is relatively easy to see when
focus has been obtained, but the condenser is too often ignored or
misused, and very, very rarely used as it is supposed to be used. It
may help to remind the reader that it is impossible to obtain a
really excellent photomicrograph unless the condenser is given
fully as much attention as is given to the objective focus.
Second only to this in importance is the nature of the illumina-
tion. Simply to see an illuminated field is far from enough. The
light must be uniform, it must be accurately centered, and the
image of the source must be brought to its focus in the correct
position, substage iris or slide, depending upon the type of illu-
mination used. The difference between an amorphous smudge
and a crisp, brilliant photomicrograph lies in a well controlled
condenser, condensing a beam of critically adjusted light.