Magnification -->how much bigger the image appears than the actual object/thing itself
Resolution -->the ability to distinguish two separate points on an image
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Light Microscopes
2 lenses:objective lens which is near the specimen and magnifies the image and the eyepiece lens where the specimen is viewed and magnified again
uses light (illumination - light underneath)
certain wavelengths are filtered to produce an image
natural colour of sample seen
maximum magnification =x 2000
maximum resolution =200nm(limiting factor)
^ lower than electron microscopes
specimens can be living or dead
inexpensive to buy and operate, small and portable, simple sample preparation, no vacuum required
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Electron Microscopy (General)
beam of electrons
wavelength less than 1nm used to illuminate the specimen
more detail, magnification high and still a clear resolution
very expensive to buy and operate
can only be used inside a carefully controlled environment in a dedicated space (large and needs to be installed)
specimens can be damaged by the electron beam
vacuum required
black and white images (can be coloured digitally)
complex preparation process-problem with artefacts (structures produced due to preparation processes, however can be eliminated as techniques improve)
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Transmission Electron Microscope (TEM)
uses electromagnets to focus a beam of electrons which is then transmitted through a specimen to produce an image
denser parts of the specimen absorb more electrons and therefore appear darker
2D image of a thin sample
maximum magnification =x 500,000
best resolution, power =0.5nm
produces black and white images
specimens are dead
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Scanning Electron Microscope (SEM)
beam of electrons sent across the surface of a specimen and reflected electrons are collected which are gathered in a cathode ray tube to form an image
produces 3D images which gives valuable information about the appearance of different organisms
maximum magnification =x 500,000
maximum resolution power =3-10 nm(not as good as TEM)
dead specimens
produce black and white images
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Laser Scanning Confocal Microscopy
fluorescent miscroscopes- higher light intensity used to illuminate a specimen treated with a fluorescent chemical (absorption and re-radiation of light)
moves a single spot of focused light across a specimen (point illumination) this causes flourescence from components labelled with 'dye'
emitted light from a specimen is filtered through a pinhole arpeture (confocal because positions of 2 pinholes- light waves and laser take same pathway)
only light radiated from very close to the focal plane (sharpest focus) is detected
Laser instead of light- higher intensities and improves illumination
very high resolution images can be obtained
2D but 3D images can be produced- images, different focal planes
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