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Today I'm going to show you how to use a compound microscope.
In the lab, the microscopes are located either in the cabinets within the lab benches,
or in the cabinets at the back of the room.
The microscopes will be covered with a plastic dust cover.
You should remove the dust cover before you move the microscope.
Bring one of the microscopes to your lab bench, using one hand to grasp the arm of the microscope,
which is the part that connects the head with the base,
and placing your other hand under the base.
Carefully carry the microscope to your bench top,
set it on the bench top in a safe position, and plug it in.
This is called the compound microscope because it has
two magnifying lens systems, in series.
This is unlike the dissecting microscopes we have used, which have a single magnifying lens.
The compound microscope has a lens close to the eye-- the ocular lens--
and it has a lens close to the object being viewed, or the objective lens.
Compound microscopes can be used to view micro-organisms, cells or cells organelles.
Two advantages of using a microscope like this-- a compound microscope compared to the unaided eye--
are magnification, which enlarges the sample, and resolution.
Resolution is the ability to distinguish two close objects as two separate entities.
Each lens has a specific resolving power,
which is the closest distance between two objects
at which they can still be observed as distinct, for that particular lens.
So as the resolving power of the lens decreases,
your ability to see two objects as distinct gets better.
In other words, a lens with a small resolving power
will allow you to distinguish between objects closer together.
Let's first describe some of the parts of the microscope.
I've already mentioned the arm of the microscope,
which is at the back of the microscope and supports the lenses.
The base of the microscope contains the light source,
and there is a switch along the side,
which turns the light on, as well as adjusting the intensity of the light source.
Above the light source is the mechanical stage,
which holds the specimen and which allows you to adjust the position of the slide.
Notice that there's a metal clip.
You should put the slide in the clip and make sure that the slide is secure.
Once the slightest secured in the clip,
you can then move the slide back and forth,
using the mechanical stage dials, which hang down along the side...
... and they will move the microscope slide back and forth...
or forward and backwards.
You also have three sets of lenses.
In the head, as I said, you have the ocular lens, which magnifies ten times.
In the nose piece, you have the objective lenses,
which have a 10x objective...
and a 40x.
The final magnification of the object is the product of the ocular magnification
times the objective magnification.
So these lenses can magnify your samples 100x,
which would be ten x times the ten x objective,
up to 400x, 10x times the 40x objective.
Below the stage is a rotating disc,
which contains the condenser lens system.
This is the third set of lenses. These don't magnify the object,
but rather concentrate light from the illumination source below,
so that it shines onto the object in a way that enhances the illumination of the specimen.
The light is focused onto the object and the object is
magnified by the objective lens.
Notice the condenser lens system can be adjusted up or down,
with the *** on the side of the microscope.
For our purposes, adjust the condenser lens system close to its highest position,
and when focusing, you want to be careful that you don't accidentally touch this ***,
instead of the magnification ***.
You also have a set of coarse adjustment knobs. These can be found on both sides of the microscope.
They're used to get the object nearly focused.
Within the coarse adjustment *** is the fine adjustment ***.
This is for bringing the object into final focus.
Let's place a specimen onto the stage.
Lower the stage, using the coarse adjustment ***,
and secure the slide with the mechanical stage clip.
Be sure the slide is secured in the clip, not on top of it or beneath it,
or it may slip when you try to move the slide around during viewing.
Turn on the light source,
and adjust the intensity of the light as needed.
You want to rotate the nose piece so that the 10x objective lens is over the slide.
You always want to start with the lowest power lens,
which has the largest field of view.
Make sure that you hear the lens click into place when you rotate it,
so that you're sure that it is seated properly and
you'll have good viewing of your specimen.
You want to raise the stage to the highest position,
using the coarse adjustment ***.
Use the mechanical stage knobs, along the side of the microscope,
to make sure that your slide is in position, directly under the objective lens.
Also, you want to make sure that the condenser lens system
is in almost the highest position.
Before viewing the sample, you should also adjust the width of the eyepieces for your own eyes,
by sliding the ocular lenses either farther apart
or closer together.
You can also adjust the focus of the ocular lens, for your own eyes,
by adjusting the diopter ring, on the ocular lenses.
This is further explained in the microscopy section of the appendix of your lab manual.
There are several different types of microscopy that one can do with this compound microscope.
One is bright field microscopy and in bright field microscopy,
you have the light source, which is shining from behind the object,
and the object appears dark against a light or bright background.
This works well for objects that have color.
If the organisms or objects are clear, they may need to be stained,
to enhance the visualization by bright field microscopy.
The disadvantage of bright field microscopy is that staining usually kills the organism.
But let's begin using bright microscopy.
You'll need to set the rotating disc in the condenser lens system to the zero position.
You will also need to adjust the iris diaphragm on the rotating disc.
This adjusts the amount of light that is allowed through the lens.
The iris diaphragm is on the front of the rotating disc of the condenser lens system. It is a little slider...
and as you open and close it, more or less light will be allowed to shine onto the object.
For bright field microscopy, you should place this
at approximately
"partial open," "half open."
Allowing too much light to pass through the lens will make the sample appear washed out,
and so when you view your sample, you may need to close the iris diaphragm further
to get better contrast on your object.
Looking through the eyepiece, you should use the coarse adjustment ***
to get the sample into focus.
Notice that by starting with the stage in the highest position,
as you move the coarse adjustment ***, the stage moves away from the lens.
This decreases the possibility that you could potentially smash the lens into your slide.
Also notice that by starting with the lowest power lens, this low-power lens is also the shortest lens,
which also helps prevent damaging the lens by hitting it with the slide.
Once you see something coming into focus with your coarse adjustment,
then you can use the fine adjustment to fine-tune your focus.
While you're working with your samples and focusing, you want to make sure that
you don't put your fingers on the lenses,
because they're very delicate and they're hard to clean.
Once you have your sample in focus with the low-power lens,
you can then switch to the high-power lens.
These microscopes are essentially what we call "parfocal,"
meaning that once you focus on the sample,
you should be able to change to another magnifying lens
and maintain relative focus.
The sample may not be completely in focus, but you should only need to make
minor adjustments with the fine-adjustment ***.
Also notice that the higher power lens is longer,
but once you have focused with the lower power lens, you should be able to
rotate the higher power lens into position over your sample, without any constraints.
This particular compound microscope can also be used for other types of microscopy,
including dark field and phase contrast.
If you wanted to view a live sample,
you could make a wet mount, and then use either the dark field or phase contrast.
In dark field microscopy,
a transparent object will appear bright or light against a dark background.
In phase contrast microscopy, the angle and diffraction of light is changed,
so that the contrast of the transparent object against the background is going to be enhanced,
so it's going to be easier to see.
To use either of these types of microscopy, you need to adjust
the rotating disc in the condenser lens system.
For dark field, you need to adjust the condenser lens system to "DF."
For phase contrast, each lens uses a different phase contrast lens system...
and you can look at the individual objective lens.
Each objective lens will be marked not only with the magnification,
but also with a "Ph" number, and this tells you
which adjustment to make in the condenser lens system.
So if you'll notice, for the 10x lens,
you need to use the "Ph 1" or "phase 1,"
so we would adjust the ring to "Ph 1."
But notice that it also has other phases-- you have phase 2, 3, and 4, as well.
In lab, we will also be doing fluorescence microscopy.
For this, we're going to use a much more specialized compound microscope.
This is connected not only to a visible light source, so we can look at bright field,
but it's also connected to an ultraviolet light source,
and we can then view the sample with both bright field and fluorescence microscopy.
When you're done, lower this stage, using the coarse adjustment,
and remove the slide.
If necessary, you can wipe off the stage with a Kimwipe.
Rotate the nose piece so that no lenses are over the stage,
and then raise the stage to its highest position.
You'll then want to turn off the light,
using the light switch dial along the side,
then unplug the microscope and carefully wrap the cord around the microscope.
So wrap the cord around just the way you found it,
replace the dust cover,
and again replace the microscope either in the cabinet by your bench,
or in the cabinet at the back of the room, again grasping the arm with one hand,
and another hand beneath the base of the microscope.
And thanks very much for watching-- we'll see you in lab.