a

Comparing Microscopes

in this video we're going to be looking

at a couple of different kinds of

microscopes and then microscopes we're

going to be talking about are the light

microscope the scanning electron

microscope and the transmission electron

microscope so let's have a little look

at our learning objectives for today

first of all gonna understand how the

three microscopes work then we're going

to hopefully be able to recognize images

from each microscope and then we're

going to suggest the advantages and

limitations for each of those three

microscopes let's get started firstly

I'd like to define this thing called

resolving power or resolution and this

is the ability of a microscope to

differentiate between two really really

close together objects or points of

light if a microscope has higher

resolution that means that it can tell

apart objects that are closer together

so it says here that higher resolution

means the objects that are closer

together can be seen as separate points

and here's an image to give the give a

little visual example of that

so on the top we have high resolution

where we can clearly see two distinct

objects and below we have low resolution

where those two objects can have merged

together into a big blurry mess so let's

look at our first microscope the light

microscope this is the way it works

we've got an eye and light is sent up

from the bottom through a condenser lens

through a specimen through an objective

lens and through an eyepiece lens and

into your eye the light is focused using

glass lenses it relies on light being

able to pass through the specimen so

that per specimens gotta be really

really thin and transparent and the

regions that absorb more light appear

darker in the image and to calculate the

magnification of a light microscope we

can look at the little number on the

eyepiece lens which pretty much most of

the time is 10 times and then multiply

that by the objective lens magnification

so most light microscopes have a a

swivel arrangement of three objective

lenses to allow you to get a little bit

closer a little bit closer a little bit

closer to your sample

so let's have a look at some images from

a light microscope

so the advantages of the light

microscope they're pretty easy to use

chances are you've used one yourself

they're really cheap to purchase we're

talking less than a thousand pounds for

a half-decent one they show true color

which means what you see is what you get

as far as the coloration of what you're

seeing sometimes we require staining no

to make make the samples easier to see

and the good thing about light

microscopes is especially if we're using

a dissection microscope we could use

live specimens but we wouldn't be able

to see inside cells so you can use it a

live specimen to look at the the

structure of an object in more detail

however the light microscope comes with

a few limitations they have a really low

resolution because of the long lazy

wavelength of light we can only resolve

apart objects that are 2 micrometers

apart they have low magnification

maximum of twelve hundred and fifty

times now this is huge for light

microscopes 1250 times is massive and

most school microscopes or college

microscopes will only be about 400 times

max mag now specimens are really thin

that we've gotta put on these slides so

because of that thinness they may not be

representing what the actual cell looks

like in its entirety let's start on

electron microscopes now now instead of

light we use electrons electrons are

brilliant because they've got a much

shorter wavelength which allows us to

resolve things that are much much closer

together so it gives us a much higher

resolution now we don't actually look

directly at the specimens themselves

though you don't look through an

eyepiece on an electron microscope

instead of computer is attached to the

electron microscope and it's going to

form an image based on how many

electrons are the density of the

electrons that are absorbed by different

areas of the specimen and then that

computer can make the image for us to

look at the first microscope the first

electron microscope is going to be the

scanning electron microscope or the SEM

and here's how it works we've got an

electron gun

got an anode to focus the beam of

electrons then we have several focusing

magnets scanning coils and electron

detectors which generate an image then

at the bottom we have the stage which

reflects the electrons back from our

sample so here we go is how it works it

directs a beam of electrons in a

specimen and it creates an image based

on the electrons they're reflected so

those that are bounced back off the

surface of the sample and the focusing

is taken care of with these

electromagnets and this is what one

looks like in real life which is kind of

cool here's some images from a scanning

electron micrograph you will notice they

have a really three-dimensional quality

to them a couple of bugs and some pollen

notice that black and white we'll get to

that in a second so I said the last ones

were black and white let's have a look

at some ones that have been false

colored so because electrons don't

correspond to wavelengths of light and

colors we have to add color digitally

based on how many electrons are absorbed

so here we have a delightful image that

has been false colored so the advantages

of the scanning electron microscope it

has a much higher resolution than a

light microscope in fact it can resolve

together resolve apart sorry objects

that are one nanometer close to each

other that is incredibly incredibly

close they provide really detailed

images of the surface structures as we

saw in our previous slide and they've

got fantastically high magnification of

about two hundred thousand times it

produces this wonderful 3-dimensional

image however there are some limitations

it's proper expensive you need a lot of

training to operate one of these devices

samples must be dead because the

electrons have to pass through a vacuum

and the stains that we use usually

contain heavy metal

which are usually somewhat toxic and it

produces a black-and-white image or a

false color image which means we cannot

get true representation of what well

what the true color of these these

specimens are we have to kind of guess

the third and final type of microscope

and the second and final type of

electron microscope we're going to look

at is the transmission electron

microscope or TEM and here's the diagram

that goes with it so again we've got an

electron being being focused with a

magnetic lens this time our electrons

are going to pass through the specimen

and onto an imaging plate which is read

by a computer so again a beam of

electrons are going to be directed at a

specimen and it's going to create an

image based on the electrons that are

absorbed not the electrons that are

reflected back like the scanning

electron micrograph and again focusing

is taken care of using electromagnets so

here's some images oh sorry my bad this

is what a transmission electron

microscope looks like please ignore in

the title top where it is SEM that

should read TEM my utmost apologies for

that we all make mistakes but this is a

transmission electron microscope let's

look at some images there's some

mitochondria some virus bits and bobs

and what looks like the Golgi apparatus

and once again we can use false coloring

to add a little bit of more excitement

to our transmission electron microscope

images and there we have a lovely

mitochondria so let's have a look at the

advantages of the TEM it's got a much

higher resolution in the light

microscope just like before one

nanometer it provides detailed images of

the interior structures of cell

organelles it's got massively high

magnification almost well pretty much

twice or over

twice that of the scanning electron

micrograph on microscope and that's

about five hundred thousand times for

what are the limitations well its proper

expensive again need loads of training

and samples must be dead for the same

reason stains are using heavy metals

which will kill cells and it takes place

in a vacuum and again black and white

images or false coloration images so

here's an further reading nice fact

sheet on microscopy and a really great

website showing 15 beautiful microscopic

images from inside the human body

to summarize electron microscopes have

greater resolution because electron

microscopes use electrons which have a

shorter wavelength and light sem that's

scanning electron microscopes produce a

3d looking image TEM that's transmission

electron microscopes produce detailed

images of the inside of cells and light

microscopes are cheaper and more

user-friendly light is focused by glass

lenses whereas electrons of focus by

electromagnets that's it thank you very

much a like comment and subscribe