4. Microscopy

Microscopes and lenses

Although cells vary in size, they’re generally quite small. For instance, the diameter of a typical human red blood cell is about eight micrometers (0.008 millimeters). To give you some context, the head of a pin is about one millimeter in diameter, so about 125 red blood cells could be lined up in a row across the head of a pin. With a few exceptions, individual cells cannot be seen with the naked eye, so scientists must instead use microscopes (micro– = “small”; –scope = “to look at”) to study them. A microscope is an instrument that magnifies objects otherwise too small to be seen, producing an image in which the object appears larger. Most photographs of cells are taken using a microscope, and these pictures can also be called micrographs.From the definition above, it might sound like a microscope is just a kind of magnifying glass. In fact, magnifying glasses do qualify as microscopes; since they have just one lens, they are called simple microscopes. The fancier instruments that we typically think of as microscopes are compound microscopes, meaning that they have multiple lenses. Because of the way these lenses are arranged, they can bend light to produce a much more magnified image than that of a magnifying glass.In a compound microscope with two lenses, the arrangement of the lenses has an interesting consequence: the orientation of the image you see is flipped in relation to the actual object you’re examining. For example, if you were looking at a piece of newsprint with the letter “e” on it, the image you saw through the microscope would be “ə.” ^{1}1start superscript, 1, end superscript More complex compound microscopes may not produce an inverted image because they include an additional lens that “re-inverts” the image back to its normal state.What separates a basic microscope from a powerful machine used in a research lab? Two parameters are especially important in microscopy: magnification and resolution.

  • Magnification is a measure of how much larger a microscope (or set of lenses within a microscope) causes an object to appear. For instance, the light microscopes typically used in high schools and colleges magnify up to about 400 times actual size. So, something that was 1 mm wide in real life would be 400 mm wide in the microscope image.
  • The resolution of a microscope or lens is the smallest distance by which two points can be separated and still be distinguished as separate objects. The smaller this value, the higher the resolving power of the microscope and the better the clarity and detail of the image. If two bacterial cells were very close together on a slide, they might look like a single, blurry dot on a microscope with low resolving power, but could be told apart as separate on a microscope with high resolving power.

Both magnification and resolution are important if you want a clear picture of something very tiny. For example, if a microscope has high magnification but low resolution, all you’ll get is a bigger version of a blurry image. Different types of microscopes differ in their magnification and resolution.

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