what is the definition of magnification?
magnification tells you how many times BIGGER the image produced by the microscope is than the real-life object you are viewing
what is the definition of resolution?
resolution is the ability to distinguish between objects that are close together
aka, the ability to see two structures that are close together as two separate structures
features of optical (light) microscopes
- optical microscopes use light to form an image
- the wave length of visible light is between 500-650 nanometers
- optical microscopes have a maximum resolution of around 0.2 micrometers or 200 nm
- light microscopes can be used to observe eukaryotic cells , their nuclei and possibly mitochondria and chloroplasts
- the maximum useful magnification of optical microscopes is about x1500
negatives of light microscopes
- optical microscopes cannot be used to distinguish between objects closer than half of the value, 500-650
- optical microscopes cannot be used to observe smaller organelles such as ribosomes, the endoplasmic reticulum or lysosomes
features of electron microscopes
- electron microscopes use electrons to form an image
- this greatly increases the resolution of electron microscopes compared to optical microscopes giving a more detailed image
- a beam of electrons has a much smaller wavelength than light so an electron microscope can resolve (distinguish between) two objects that are extremely close together
- maximum resolution of around 0.0002 micrometers or 0.2 nm
- can be used to observe smaller organelles such as ribosomes, endoplasmic reticulum or lysosomes
- the maximum useful magnification is around x1,500,000
what the the two types of electron microscope?
transmission electron microscope (TEMs) and scanning electron microscope (SEMs)
features of transmission electron microscopes (TEMs)
- use electromagnets to focus a beam of electrons
- the beam of electrons is transmitted through the specimen
- denser parts of the specimen absorb more electrons, this makes the denser parts appear darker on the final image produced
advantages of TEMs
- give high resolution images (more detail)
- this allows internal structures within cells to be seen
disadvantages of TEMs
- only can be used on very thin specimens or thin sections of the object
- they cannot be used to observe live specimens as there is an vacuum inside and all the water much be removed from the specimen, unlike optical microscopes
- they do not produce a colour image, unlike optical microscopes
features of scanning electron microscopes (SEMs)
- SEMs scan a beam of electrons across the specimen
- This beam bounces off the surface of the specimen and the electrons are detected, forming an image
- This means SEMs can produce three-dimensional images that show the surface of specimens
advantages of SEMs
- They can be used on thick or 3-D specimens
- They allow the external, 3-D structure of specimens to be observed
disadvantages of SEMs
- They give lower resolution images (less detail) than TEMs
- They cannot be used to observe live specimens (unlike optical microscopes that can be used to observe live specimens)
- They do not produce a colour image (unlike optical microscopes that produce a colour image)
features of laser scanning confocal microscopes
These microscopes are relatively new technology
- The cells being viewed must be stained with fluorescent dyes
- A thick section of tissue or small living organisms are scanned with a laser beam
- The laser beam is reflected by the fluorescent dyes
- Multiple depths of the tissue section/organisms are scanned to produce an image
Think of it like the laser beam is building up the image layer by layer
advantages of laser scanning confocal microscopes
- They can be used on thick or 3-D specimens
- They allow the external, 3-D structure of specimens to be observed
- Very clear images are produced. The high resolution is due to the fact that the laser beam can be focused at a very specific depth
- You can even see the structure of the cytoskeleton in cells
disadvantages of laser microscopes
- It is a slow process and takes a long time to obtain an image
- The laser has the potential to cause photodamage to the cells
how do optical microscopes work
- light is directed through a thin layer of biological material on the glass slide
- this light is focused through several lenses so that the image is visible through the eyepiece
- the magnifying power of the microscopes can be increased by rotating the objective lens to the higher setting
