Magnification and Resolution

Two ideas describe how well a microscope shows a specimen: magnification and resolution.Magnification is how many times bigger the image is than the real object:magnification = image size ÷ actual sizeResolution (resolving power) is the smallest distance between two points that can still be seen as two separate points. The smaller this distance, the higher the resolution and the more detail you can see. Magnifying an image beyond the limit of resolution just makes a bigger blur; no extra detail appears.Resolution is limited by the wavelength of the radiation used. Light has a much longer wavelength than a beam of electrons, so a light microscope can resolve about 200 nm, while an electron microscope can resolve objects well under 1 nm.Always use the same units for image size and actual size:1 mm = 1000 µm    1 µm = 1000 nmWorked example. A mitochondrion is 20 mm long in a photograph with a magnification of ×8000. Convert the image size: 20 mm = 20 000 µm. Rearranging, actual size = image size ÷ magnification = 20 000 ÷ 8000 = 2.5 µm.The formula can be rearranged to find any one of the three quantities. A scale bar on a micrograph lets you work out magnification: measure the bar, convert to the same unit as its label, then divide the measured length by the length it represents.