Light microscope
TEM
SEM
uses light to produce images
uses electron beams to produce images
uses electron beams to produce images
Maximum resolution
200 nm
1 nm
1 nm
Maximum magnification
× 2000
up to × 1 000 000
× 200 000
Preparation of material
thin sections of material mounted very thin sections of material on slides supported on metal grids MJWJOH PSHBOJTNT DBO CF FYBNJOFE MJWJOH PSHBOJTNT DBOOPU CF FYBNJOFE
very thin sections of material supported on metal grids living organisms cannot be FYBNJOFE
Stain used
coloured dyes
heavy metals
carbon or gold coating
Image
viewed directly through eyepiece lens
viewed on a screen or photographic plate
viewed on a screen or photographic plate
Table 1.1 Comparison of light microscopes with transmission electron microscope (TEM) and scanning elelctron microscope (SEM).
Magnification and scale Knowing the sizes of objects viewed under the microscope can be very useful (Figure 1.5). For example, a plant scientist might want to compare the relative sizes of pollen grains from plants in the same genus to help identify different species. Magnification is defined as the ratio of the size of the image to the size of the object: magnification =
size of image size of object eyepiece lens
focusing knobs objective lenses
slide
stage mirror to direct light
Figure 1.5 Typical compound light microscope.
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