Thames & Kosmos TK2 Scope, Руководство по эксперименту

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Using the Microscope with Transmitted Light
In the last section, you learned quite a lot that will help you with using the micro-
scope. Nevertheless, we suggest that you still read this section carefully in order to
avoid mistakes later when you start your microscopic explorations.
What do you need for the next exercise? Of course, the first thing is an object. The
best thing to use in order to become familiar with the microscope is one of the
prepared slides included in the kit.
First, set the toggle switch for the illumination to “I.” The light comes on from
below. Then fasten one of the prepared slides under the stage clips. Incidentally,
these can be lifted up by pressing lightly on the short sides of the clips. Push the
slide under the clips and, at the same time, make sure that the object (see illus-
tration) is lying directly over the hole through which the light from the lamp is
shining.
Now we proceed as already described for the magnifying glass. Slowly raise the
stage by turning the knob and bring the object into focus. Once you have ob-
served the object at this magnification, turn the revolving nosepiece clockwise to
the yellow (10x) and finally to the blue objective (40x). Now you are looking at the
object with the highest possible magnification. It’s enlarged 400 times!
A word on the aperture wheel (the rotating disk) underneath the stage: When
you turn it, you will see that openings of different sizes open up in the disk. You
would think that, as a matter of principle, the largest opening — which lets the
most light through — is also the best. But that is not always the case. Sometimes
you can see more with less light! However, there is no rule of thumb for this. You
will need to simply try it out with your specimens to see whether you get a better
image with a different setting of the aperture wheel.
When using the blue objective lens, a special level of fine tuning is needed. If you
raise the stage too high so that it bumps against the cover slip on the underside of
the objective, then this can cause two problems:
1. The cover slip or even the slide can break and your prepared slide (or whatever
it is that you happen to be looking at in that moment) is destroyed.
2. The sensitive lens on the underside of the objective can be scratched and, in the
best-case scenario, from now on you will always see these scratches. In the worst-
case scenario, you will not be able to see anything clearly through the scratched
objective.
If the objective lenses should get dirty at some point, then clean them carefully
with a sheet of lens cleaning paper. When you do so, do not use any water or
cleaning agents! The same also applies to the ocular lens, which gets dirty again
and again from the oil on your eyelashes (this can’t be avoided) and consequently
has to be cleaned regularly. Last but not least, here’s another tip: From my own
experience, I suggest that you start with the red (4x) objective for each new object
and then work up to the yellow (10x) and then to blue objective (40x). Many ob-
jects can be seen sufficiently at the smallest magnification. Moreover, it is helpful
to always gain an overview of an object before looking at individual details at the
strongest magnification.
How does the microscope actually “make” the magnification? And why does the
image in the microscope move left even though you move the slide right? In the
next section, which is about the inner workings of your microscope, you will find
the answer to these questions.
There’s a funny black streak in my image…
The ocular of your microscope is equipped with a so-called “ocular pointer.”
There is a fine wire with a needle tip on the inside that can be rotated when
looking through the ocular lens (and moving the object) in such a way that
it points, for instance, to certain cells or other interesting areas of the object.
This makes it easier to show these areas to others.
If the pointer bothers you during everyday use of the microscope, the wire
can be removed quite easily from the ocular using the tweezers (and put back
in again later). To do this, you simply take the ocular out of the tube. Have an
adult help you with this so that the sensitive lens in the ocular is not scratched.
It’s best to store the fine wire in an envelope or a small bag in the microscope’s
box so that it isn’t lost.
Use as a transmitted-light microscope
Using the pointer (here, the pointer is pointing to
a cell nucleus.)
Removing the pointer tip from the ocular
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