Microscope field of view calculator

See how much of the specimen fits within the eyepiece view.

Choose your optics

Use the magnification marked on the objective. For a zoom microscope, enter the current objective/zoom magnification here.

Look for a marking such as 10×/22. The 22 is the field number. Eyepiece magnification alone does not set the visible field diameter.

Leave at 1× unless your microscope has another magnifying component in the observation path.

Approximate specimen field diameter
0.550 mm
550 µm across
Visible circular area0.238 mm²
Viewing magnification400×

FN 22 ÷ (40× objective × 1× tube factor)

Specimen view · scale diagram

0.55 mmfield diameter
Stylised cells · grid scaled to the selected field

Grid spacing: 0.1 mm. Illustration is to scale for the selected field diameter.

General guide. The calculation assumes that the objective and viewing tube support the eyepiece field number. A field stop, vignetting, zoom configuration or camera can reduce the area actually visible. Confirm the field with a stage micrometer for measurement work.

What changes the field of view?

A larger eyepiece field number shows a wider specimen area. A higher objective magnification or an additional magnifying tube factor shows a smaller area. Changing eyepiece magnification alone does not change this diameter when FN is held constant, though it changes viewing magnification.

Formula: specimen field diameter (mm) ≈ eyepiece FN (mm) ÷ [objective magnification × intermediate/tube factor]. The circular area is π × (diameter ÷ 2)². The field diameter and grid are calculated. The cell drawing is illustrative and does not represent a calibrated specimen. Presets are generic examples: match your actual markings and microscope configuration. This tool does not calculate optical resolution or depth of field.

Auckland Scientific educational guide. Read more: Nikon MicroscopyU: field of view · Evident: eyepieces and field number.

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