SPECIMEN MEASUREMENT
The measurement of specimen size with a microscope is normally made by using an eyepiece micrometer. This is a glass disc with a scale etched onto its surface, which can be inserted into most (but not all) eyepieces. Alternatively a specialised measuring eyepiece which has a scale permanently fitted is used.
Brunel Microscopes offers both types for compound microscopes and complete measuring eyepieces for stereomicroscopes. These are listed in the accessories of the various microscopes. Which ever type is preferred, the image of the eyepiece micrometer (scale) is superimposed on the specimen image, both being in focus at the same time. In other words the specimen appears to have a ruler lying across it.
Clearly the size of the eyepiece scale remains constant, despite the fact that the image viewed will change its size depending on the objective magnification chosen. For example a pollen grain viewed with the x40 objective will appear down the microscope very much larger than when viewed with the x10 objective. However because the micrometer scale is in the eyepiece it will not change its size. The real value of each of the eyepiece scale divisions therefore varies with the objective magnification. It is necessary therefore to calibrate the eyepiece scale with a real scale placed on the microscope stage for each potential magnification to be used. This is called a stage micrometer, and is in effect a very accurately etched ruler in the centre of a microscope slide. Usually the scale is 1 mm divided into 100 parts or 1cm divided into 1000 parts.
To calibrate the eyepiece micrometer, the stage micrometer has to be focused using the objective to be used. If the normal eyepiece is then replace by the measuring eyepiece it is possible to line up the eyepiece and stage scales so that they superimpose. Since the stage micrometer is a real scale it is then possible to calibrate the value of each eyepiece division AT THAT MAGNIFICATION. This has to be repeated for all possible magnifications and the results recorded for future use. In summary therefore to make specimen measurements the following are required
Compound or high power microscopes
Either a 19 mm eyepiece micrometer disc which can be placed into an existing eyepiece - providing the eyepiece has a retaining shelf internally. This can be seen by removing the top lens of the eyepiece - or a complete micrometer eyepiece with a scale already in place.
A stage micrometer
Stereomicroscope
A complete eyepiece micrometer
A stage micrometer
If you need advice on special point counting eyepieces or grid square eyepieces please E-mail
Brunel Microscopes offers both types for compound microscopes and complete measuring eyepieces for stereomicroscopes. These are listed in the accessories of the various microscopes. Which ever type is preferred, the image of the eyepiece micrometer (scale) is superimposed on the specimen image, both being in focus at the same time. In other words the specimen appears to have a ruler lying across it.
Clearly the size of the eyepiece scale remains constant, despite the fact that the image viewed will change its size depending on the objective magnification chosen. For example a pollen grain viewed with the x40 objective will appear down the microscope very much larger than when viewed with the x10 objective. However because the micrometer scale is in the eyepiece it will not change its size. The real value of each of the eyepiece scale divisions therefore varies with the objective magnification. It is necessary therefore to calibrate the eyepiece scale with a real scale placed on the microscope stage for each potential magnification to be used. This is called a stage micrometer, and is in effect a very accurately etched ruler in the centre of a microscope slide. Usually the scale is 1 mm divided into 100 parts or 1cm divided into 1000 parts.
To calibrate the eyepiece micrometer, the stage micrometer has to be focused using the objective to be used. If the normal eyepiece is then replace by the measuring eyepiece it is possible to line up the eyepiece and stage scales so that they superimpose. Since the stage micrometer is a real scale it is then possible to calibrate the value of each eyepiece division AT THAT MAGNIFICATION. This has to be repeated for all possible magnifications and the results recorded for future use. In summary therefore to make specimen measurements the following are required
Compound or high power microscopes
Either a 19 mm eyepiece micrometer disc which can be placed into an existing eyepiece -
Stereomicroscope
A complete eyepiece micrometer
A stage micrometer
If you need advice on special point counting eyepieces or grid square eyepieces please E-
Slide micrometer scale (large stippled figures), eyepiece scale (small solid figures)
BRUNEL MICROSCOPES LTD
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