Microscope Technology
The Greenbelt doctor uses a microscope in a local newspaper from December
1940.
One of the main advances in microscopes during the twentieth
century, was standardization of parts. With the demands of World War I on
supplies, microscopes could no longer be manufactured by hand. The large
number of unskilled workers in the work force, imposed upon the industry
to create precision tools. With this new emphasis on precision tools,
standardization of parts was possible.(12)
One of the first parts to become standard was the eyepiece. By 1940
almost all the eyepieces being manufactured were 23 mm diameter, short
tube length. Also the move away from highly polished or grained brass
marks the microscopes of the early twentieth century. It was discovered
that blackened japan on cast-iron was far more durable. As a result most
microscopes of the time have a blackened finish. This also supplies more
weight to the microscope, especially the base. With the added weight
at the bottom of the microscope there was greater stability, a problem of
earlier microscope designs.(13)
The making and labeling of the objectives also was standardized. The
original manufacturers of microscopes were British and American, so
the objectives were originally labeled in inches of the diameter. Then as
manufacturing became more international, the objectives were labeled by
diameter in mm. By 1940 the labeling of the objectives was (and still is)
by magnification. So an objective could have been called a 2/3", 16mm and
a 10x.(14)
There were of course many different varieties of
microscopes being manufactured in the 1940's, but most of them had the
same general parts:
The base is the support for the entire microscope. This is
where the most weight should be, so that the telescope is well balanced.
In many cases the base is a horse-shoe shape. The base is then connected
to the limb by a hinge. The rest of the microscope can tilt
away from the base on the hinge. The limb supports the rest of the
microscope. This includes a substage mirror/light source. The
light is to be shown up through the specimen and in to the optical tube.
Above the light, connected to the limb, is the stage and in some
cases a substage. It is on the stage that the specimen is placed.
The substage can have many purposes, most commonly it holds an iris to
control the amount of light passing through the specimen. There will be
some kind of slide holder and a translation table to systematically move
the specimen around. Attached to the upper part of the limb is the
body. The body holds the optical components including the
eyepiece for some magnification and to focus the light beam on
your eye. At the other end of the body are the objectives. The
objectives are what produce the bulk of the magnification. The body can
be moved up and down with coarse and fine adjustments. The allows
the observer to focus on different depths of the specimen.(15)
The coarse focusing up to and including the 1940's was almost always
a rack and pinion setup. This is that as the knob is turned, a set of
threads on the knob interacts with threads on the body, thus moving the
body up and down. The fine adjustment was originally also a set of
threads, only narrower or ball-bearing motion. By the 1940's this had
changed so that the most common fine adjustments were using crank and
lever motion. In this case as the knob rotates it screws in or out.
At the end of the screw is a lever that is connected to the body. When
the screw is moved in, it pushes on one end of the lever and forces the
other end up as well. Having this lever arm increases the sensitivity of
the turns, so that it is easier to make fine adjustments.(16)
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