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10 mm Scale


HOW TO READ AN EYEPIECE MICROMETER


What is the scale factor of the eyepiece retical while using different objective lenses?


Original scale, 1X = 10 mm with 100 divisions. Each minor division = 0.10 mm

At 1X (no magnification) each minor division is 0.10 mm or 100 Microns

With a 4X Objective each minor division is 0.025 mm or 25 Microns

With a 10X Objective each minor division is 0.010 mm or 10 Microns

With a 20X Objective each minor division is 0.005 mm or 5 Microns

With a 40X Objective each minor division is 0.0025 mm or 2.5 Microns

With a 50X Objective each minor division is 0.002 mm or 2 Microns

With a 60X Objective each minor division is 0.00167 mm or 1.67 Microns

With an 80X Objective each minor division is 0.00125 mm or 1.25 Microns

With a 100X Objective each minor division is 0.001 mm or 1.0 Micron

For the measurements above, the magnification of the eyepiece is not considered since the eyepiece magnification is applied equally to the image field and to the eyepiece scale.

An eyepiece with a Field Number of 20 (F.N. 20) has a 20 mm diameter Field Stop. The diameter of the visual field while using different objective lenses is…
4X Obj. = 5000 microns    10X Obj. = 2000 microns    20X Obj. = 1000 microns
40X Obj. = 500 microns    50X Obj. = 400 microns    60X Obj. = 333 microns
80X Obj. = 250 microns    100X Obj. = 200 microns