Magnification and Resolution

• Magnification


  How many times bigger the image of a specimen observed is in comparison to the actual (real-life) size of the specimen
• Magnification Formula


  Magnification (M) = Image/Imaging Size (I) / Actual Size of Specimen (A)
• Units for measuring cell size

  • Micrometres (μm) or nanometres (nm)
• Converting units


  Multiply or divide by 1000 depending if the units are increasing or decreasing
• Magnification does not have units
• Eyepiece lens


  Often has a magnification of x10
• Objective lens


  Series of (usually 3) lenses, each with a different magnification
• Calculating total magnification


  Eyepiece lens magnification x Objective lens magnification = Total magnification
• Resolution


  The ability to distinguish between two separate points
• If two separate points cannot be resolved, they will be observed as one point
• Resolution of light microscope

  Limited by the wavelength of light
• Electron microscopes have a much higher resolution and magnification than a light microscope as electrons have a much smaller wavelength than visible light
• The concept of resolution is why the phospholipid bilayer structure of the cell membrane cannot be observed under a light microscope
• The maximum resolution of a light microscope is 200nm (half the smallest wavelength of visible light, 400nm)
• Any points that are separated by a distance less than 200nm (such as the 10nm phospholipid bilayer) cannot be resolved by a light microscope and therefore will not be distinguishable as "separate"