I want to discuss something I noticed today while cleaning my microscope desk and lenses.
I have two ocular micrometres of different tube lengths. So I, while checking and experimenting on the stereomicroscope, I discovered something which made me wonder and worry.
Using the same subject (letter R of a receipt), I put the adjustable eyepiece setting of the stereomicroscope all way up and then all way down and realised that the length of the 'R' varied from 16 to 20 divisions (c. 25% difference). I repeated this with the other micrometer. R measured differently between 19 to 23 divisions - four different readings for the same subject!!!. I was not aware that this would have any effect (never been told during courses on microscopy). It may be a potential source of error when measuring spores in the light microscope if the microscope eyepiece tube goes up and down (not the lens itself)
So this makes calibration a bit more awkward and the following steps should be adopted:
1. Put the micrometer always on the same eypiece and set it fixed in middle way setting (o).
2. Focus compensation between eyepieces should hence be done on the other eyepiece only
3. Using this fixed setting, perform callibration for each micrometer
I thought this is good to share and discuss!