Hello I'm Professor Murry Gans and I would like to welcome you to the non majors
biology lab here at Eastfield College in Mesquite, Texas
What we're going to do today is show you how to use the light microscope.
That way you'll know exactly what to do before you come to lab.
So what do you say? Let's get Started.
When you need a microscope for a lab they're stored in this cabinet.
Grab the microscope with the handle on the arm. Support it with your other hand
under the base. Hold it close to your body and take it to your table.
Before we talk about the parts of the microscope
let's talk about what the microscope is going to do.
The microscope uses a series of lenses that magnify an object.
Now this hands lens will magnify up to 20 to 30 times.
We want the microscope to magnify up to 400 times for us.
To do that it's going to use a more than one lens. A series of lenses. Let's take a look.
At the top of the microscope are the eyepieces or Oculars.
These magnify our specimen 10 times.
The second set of lenses are down here. These are the objective lenses.
The short one is the 4x lens.
The next one is the 10x lens, or medium power.
And the next one is the 40x lens or high power.
They're mounted on the revolving nosepiece which let's you change them easily.
There are 3 different adjustments for the light on this microscope.
You have the power switch here. Which turns the light on.
We also have a ring mounted under here which is called the Diaghragm.
By moving the ring of the diaphragm, I can control the amount of light that reaches the specimen.
I can control it all the way from very bright to very dim.
The third light adjustment is right here. Just a regular dimmer switch.
This part of the microscope is called the Stage.
and on it is a mechanical stage. This is what's going to hold the slide
and let us move it around.
To put a slide on the microscope, simply pull this arm back.
Slide the slide into the angle and let go of the arm.
We're going to move the slide around by moving these 2 knobs.
This knob moves the slide up and down.
This knob moves the slide left and right.
To focus the image in our microscope, there are 2 focusing knobs.
The one on the outside is called the coarse focus knob.
The one on the inside is called the fine focus knob.
You'll notice that when I use the coarse focus knob, the stage moves a lot.
When I turn the fine focus knob, it moves in very small increments.
The eyepieces are adjustable.
So when you look through the microscope you want to adjust them so that they
only form a single image.
Before you use your microscope, you want to clean all the lenses.
So we're going to use a little bit of lens paper.
So just take one sheet of this. Tear it out of the booklet.
You're going to wad it up. You're going to use that sheet to clean each of the eyepieces.
And you also want to clean each of the objective lenses.
Just wipe them down a little bit.
I also like to go ahead and clean the top of the diaphragm.
In biology we often mount things in water.
We use a technique called a wet mount slide.
So here's my microscope slide.
And for a specimen, we've cut a piece of paper out
with the printed word slide on it. So I'm going to use my forceps and put that on my slide.
We're going to use a little bit of water.
We're going to add a drop of water to our specimen. Whatever it is.
Then I'm going to use some cover slips.
You want to only use one cover slip. They're very very thin. Here's your cover slip.
Now the trick to make a good slide is to not have air bubbles.
So if you'll take your cover slip and move it toward the water, then when the water spreads
out like that, just drop the cover slip.
And that way you get a very nice slide with very few air bubbles.
When getting ready to focus the image on the microscope
we're going to start off with low power.
We start with the lower power objective because it has the largest field of view.
What that means is we're going to see more so you can find what you're looking for.
It's really important especially if it's a really small specimen.
First thing we're going to do with this on low power
is bring the stage all the way up. It will stop.
Then I'm going to look through the eyepieces and I'm going to turn the coarse adjustment
knob away from me.
Until I get my image into focus.
Then I'm going to use the fine adjustment knob to really get that sharp focus.
Now it's a good point now to use the diaphragm to adjust the light.
Sometimes turning the light down just a little bit will let you see a lot more details.
At this point, what we want to do is center the specimen.
and then go to medium power.
To go to medium power I'm simply going to click the medium power lens into place.
So with medium power, I'm going to look through the eyepiece.
I'm going to use my coarse adjustment
a little bit. Fine focus again and don't forget use your diaphragm.
to get those good details.
And now I'm going to use the mechanical stage and I'm going to center again.
At this point, I'm ready to go to high power.
Now the focal length, the distance between the lens and the slide
is very short with high power. In fact, you're going to think you're going to hit the slide
so you're going to watch from the side and it should click into place.
If you focus on low power and medium power, the high power
objective should actually clear the slide just fine.
Here I'm going to probably just use my fine focus
to get a nice image. I'm going to look around a little bit. And don't forget, adjust your light.
Play with the dimmer. Play with the diaghragm to get the image that you want to see.
You'll notice that I keep saying focus and center
It's important that you center the specimen before you increase the magnification.
Imagine that I'm the specimen. On low power you might see this much of me
but on high power you might see the area the size of my shirt button.
And if I'm like this and we're a little bit off center when you go into high power you might
be focusing right there. In which case you'll see absolutely nothing.
When you're through with your microscope, you want to put it away properly.
First of all, don't forget to take off your slide. The cover slip is disposable.
your instructor will tell you where to put that. The slide should be washed and returned to the
slide box. Turn the light off on the scope.
Unplug the scope. Now you're going to wrap the cord up. Unplug the scope
and wrap it up.
Cover your scope again with the microscope cover.
And you're going to carry it back to the cabinet.
Remember, grab by the arm and support by the base.
Be aware that if the light's been on, the base might be a little warm
so you can cup your hands so you don't get burned.
Let's review what you should've learned from this video. You should know the parts
of the microscope. You should know how to carry the microscope. How to set it up.
How to make a wet mount slide and how to get that image in focus.
Remember you always want to go from low power to medium power to high power.
You should also know the magnification of all the lenses, the eye piece and all 3 objectives.
The nice thing about videos like this, is if you miss something just watch it again.
The nice thing about videos like this is if you miss something, just watch it again.
To be successful in college, it is important to come to class prepared.
Be sure to read the chapter before coming to lecture.
And definitely read the lab procedure before you come to lab.
It will make all the difference in how much you get out of your classes.
For now this is Murry Gans at Eastfield College in the biology lab. See you next time.