Microscope Magnification Calculator
Find the total magnification of a compound microscope from the eyepiece and objective, plus the field-of-view diameter when you switch objectives.
How it works
Total magnification = eyepiece × objective · FOV(high) = FOV(low) × (objective_low ÷ objective_high)
A compound microscope magnifies in two stages: the objective lens forms a magnified image, and the eyepiece magnifies that image again, so the total is their product. The field of view — the diameter of the circle you can see — shrinks in inverse proportion to the objective power, because a stronger objective spreads a smaller patch of the specimen across the same eyepiece. Knowing the field width at one objective lets you calculate it at any other.
Worked example
A 10× eyepiece with a 40× objective gives 10 × 40 = 400× total magnification. If the field of view is 2 mm at the 4× objective, then at 40× it is 2 × (4 ÷ 40) = 0.2 mm across.
Sources: Optical microscope — Wikipedia
Frequently asked questions
How do I calculate total magnification?
Multiply the eyepiece (ocular) magnification by the objective magnification. A common 10× eyepiece with objectives of 4×, 10× and 40× gives total magnifications of 40×, 100× and 400×.
Why does the field of view shrink at higher power?
A higher-power objective magnifies a smaller area to fill the same eyepiece view, so you see less of the specimen. The field diameter is inversely proportional to objective power — switching from 4× to 40× cuts the field to one tenth.
How is field of view measured?
You can measure it directly by placing a clear ruler on the stage at low power and reading the diameter of the visible circle. From that reference, the field at any other objective follows from the ratio of the objective powers.
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Educational estimate, not medical advice — verify formulas, units and assumptions for your specific case.