2.1.1 F) Difference between Magnification and Resolution Flashcards
Magnification
how enlarged the image is compared to the original object
Resolution:
the ability of a microscope to distinguish between 2 separate adjacent points on an image as 2 separate objects
Comparison of electron and light microscope magnification and resolution:
Magnification: light → LSCM → SEM → TEM
Resolution: light → LSCM → SEM → TEM
How do light microscopes work?
use glass lens that focus a beam of light onto specimen on the slide (image produced is called a photomicrograph)
When are light microscopes used?
used for visualising whole cells or tissues
Magnification of light microscope:
2,000 x
Resolution of light microscope:
0.2 µm
- not large enough to visualise any of the smaller organelles
Advantages of light microscopes:
- can visualise living cells so we can watch behaviours such as cell division in real time
- cheaper
- portable
- images in colour
- require minimal training to use
Disadvantages of light microscopes:
- lower magnification and lower resolution compared to electron microscopes - so produce less detailed images
- presence of light
How does a TEM work?
- uses electromagnets to focus a beam of electrons at a specimen/sample
- which is then transmitted through the specimen to produce 2D images (electron micrograph)
- denser parts of the specimen absorb more electrons which makes them look darker on the image you end up with
When are TEMs used?
to view thin specimens (tissue sections, molecules, etc) through which electrons can pass generating a projection image
Magnification of TEM:
2,000,000x
Resolution of TEM:
0.1 - 4 nm
Advantages of TEM:
- electrons have much shorter wavelength compared to visible light which means higher resolution detailed images can be produced
- higher max magnification and max resolution than light microscope and SEM
Disadvantages of TEM:
- sample needs to be fixed and placed in vacuum so cannot be used on living specimens
- very expensive
- large - not portable
- lack of availability - only found in specialised research facilities and hospitals
- training required to use
- metal stains used can be toxic/hazardous
- very large → not portable
How does a scanning electron microscope work?
- emit beam of electrons towards a sample knocking electrons off specimen
- which are gathered in cathode ray tube and then used to form an image
When are SEMs used?
in materials science for research, quality control and failure analysis
Magnification of SEM:
500,000x
Resolution of SEM:
10 nm
- lower resolution than TEMs
Advantages of SEM:
- high magnification and high resolution (compared to light microscopes) so produce clearer images than light microscope
- can produce 3D images with depth of field
- can be used to look at the specimen at different depths so image not confused bu other components that are not in focus
- good for viewing surfaces
Disadvantages of SEM:
- image is interpretation rather than real life image
- lower max resolution than TEMs
- lower max magnification than TEMs
- sample needs to be fixed and placed in vacuum so cannot be used on living specimens
- very expensive
- large - not portable
- lack of availability - only found in specialised research facilities and hospitals
- training required to use
- black and white (but artificial colouring can be added)
How does a laser scanning confocal microscope work?
uses laser light to scan the slide point by point and assemble/compile one image using a computer
When are LSCM’s used?
- used in medicine (for quick and effective diagnosis) and biological research
- not used much for magnitive powers
Magnification of LSCM:
x17,820
Resolution of LSCM:
800nm
Advantages of LSCM:
- high resolution
- high contrast images - can see difference between tissues well
- have depth selectivity - so can be used for whole living specimens and cells and can make 3D images of cells
- suitable for viewing thick specimens
Disadvantages of LSCM:
- much more expensive than normal light microscope
- lasers in older versions can damage cells
- formation of a “stack” of images can be time consuming as the microscope has to scan the image many times in layers
- slower imaging speed
- stain may need to be used
- high powered laser can damage eyes
- can be time-consuming
- lose perception of colour
