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Microscopy Measurements

posted Nov 21, 2018, 8:56 AM by Helen Mooney   [ updated Nov 22, 2018, 1:53 PM ]
One of the more common microscope accessories is an eye-piece graticule (EPG).  It is an eye-piece with a scale incorporated into a ocular 10X lens.  It can be used to measure all manner of things such as venation in wings- believe it or not, different sub-species, have different patterns, and key points can be measured and referenced.  This is called wing morphometry and it was very popular before DNA research became accessible to beekeepers. Another is pollen measurements.  Measuring pollen in a sample of honey helps us to identify the plant source and ultimately gives us an idea of the forage available when the nectar associated with that plant, was abundant. 

As you can imagine, the divisions on the EPG scale, equate to vastly different measurements at different magnifications.  At each magnification, the eye-piece graticule must be calibrated against a reference.  This reference is called a stage micrometer (SM). This is a microscope slide with an accurate scale.  We count 100 divisions on the EPG and compare it to the stage micrometer. Generally at 10X, the scale almost exactly superimposes the stage micrometer scale, but there is always a slight margin of error. The manufacturers guarantee that the SM scale on such a slide is highly accurate.  The stage micrometer we use has three scales.  The centre scale is most suited for our needs.  It is 1mm in length, has 100 divisions, so each division is 10 microns (0.01mm, as labelled on the slide).  The EPG is calibrated at each magnification and on each microscope used.  This procedure does not ever have to be repeated.  We just document the measurements. 

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