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Presets fill in a figure only where its maker publishes one, with the source shown.
Tools
Microscope field of view calculator
Enter your eyepiece's field number, the objective and your camera's sensor size to see how much of the sample you'll see and photograph.
Free tool · no signup
Through the eyepiece
Field of view = field number ÷ objective magnification. Nikon's MicroscopyU gives this formula, and says an auxiliary lens between the objective and eyepiece is multiplied into the objective magnification first.
An eyepiece with an 18 mm field number and a 10X objective shows a circle 1.8 mm across. AmScope lists 18 mm for the T490B's 10X eyepiece.
Eyepiece field numbers are often missing from product pages. When you can't find yours, ask the maker for it.
On the camera sensor
A camera sees the sensor's size divided by the total magnification from the sample to the sensor, as Leica Microsystems explains. With a C-mount adapter, that total is the objective times the adapter.
A 1/2 inch sensor has an 8 mm diagonal, according to Teledyne's lens selection note. Behind a 0.5X adapter and a 10X objective it covers 1.6 mm of the sample, corner to corner.
Why photos get dark corners
Evident advises choosing an adapter so the sensor diagonal divided by the adapter magnification stays inside the image circle of the tube lens. A bigger result lets the sensor reach past the lit circle, and the corners go dark.
Camera ports rarely list their image circle, so the calculator compares against the eyepiece field number as an estimate. AmScope makes the same comparison, suggesting eyepieces with field numbers close to the sensor diagonal.
AmScope sells its AD-C05-CX 0.5X adapter for 1/2 inch sensors. By Evident's rule, 8 mm ÷ 0.5 = 16 mm, inside an 18 mm field.
Common questions
Divide the eyepiece's field number by the objective magnification. An 18 mm field number with a 10X objective shows a circle 1.8 mm across.
The sensor's size divided by the total magnification from the sample to the sensor. A 1/2 inch sensor behind a 0.5X adapter and a 10X objective covers 1.6 mm, corner to corner.