2.1.3 Measuring objects seen with a light microscope

2.1.3 Measuring objects seen with a light microscope

1. Using graticules

   • Microscope eyepiece= fitted with graticule
     • Graticule= transparent with a small ruler etched on
       • The scale is arbitrary - represents diff. lengths at diff. magnifications
     • As a specimen is viewed the eyepiece graticule scale is superimposed and the dimensions of specimen can be measured in epu
     • Eyepiece scale has to be calibrated for each different objective lens by using a stage graticule
       • Stage graticule= precise measuring divide with a small scale to calibrate value of eyepiece divisions at different magnifications

2. Using a stage graticule to calibrate the eyepiece graticule

   • A stage graticule, microscopic ruler, is placed on the microscope stage
     • Ruler is 1mm long with 100 divisions= each division is 0.01mm or 10um
   • 1) Insert eyepiece graticule in X10 eyepiece of microscope
   • 2) Place a stage graticule on microscope stage, bring to focus, use low power X4 objective. T. magnification= X40
   • 3) Align eyepiece and stage graticule. Check value of 1 eyepiece division
   • 4) In the example, stage graticule (1000um) corresponds to 40 eyepiece divisions
   • 5) Each eyepiece division= 1000/40 = 25um
   • 6) Now use X10 objective lens (T. magnification is X100) and focus on stage graticule
   • 7) Align both graticules
   • 8) From the example, 100 eyepiece divisions correspond with 1000um
   • 9) So one eyepiece division= 1000/100= 10um

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