Focusing on the Field of View

Inverted metallographic microscopeWhen magnification was as simple as one eyepiece and one objective, finding your total magnification was as easy as multiplying the two values together. The addition of film brought a third value to the equation, but the result remained a static, concrete number.

And then along came the computer.

With a huge variety of video camera chips and monitor sizes and camera couplers and screen resolution, suddenly viewing something at 500X magnification became much more challenging. There was no way to take into account all of the permutations possible. For example, even if two systems were otherwise exactly the same, but one had a 23″ monitor and the other had a 24″ monitor, the magnification would be different.

It was time to replace the magnification focus with a different way of looking at things: the Field of View (F.O.V.)

F.O.V. describes the amount of the sample that can be seen, as opposed to how much bigger we can see the sample. No matter how the screen resolution or monitor size changes, the F.O.V. can remain constant.

This becomes critical when dealing with standards. Standards are used to reference very specific magnifications for measuring samples. Your lab would have wall charts with photos of samples at varying magnifications so you could compare your results with what was expected. However, when your 500X magnification doesn’t match my 500X magnification, using magnifications for standards becomes an impossible challenge.

Standards are changing to reflect the improvement in technology. Todays standards require pixel calibration values or specific F.O.V.s for measuring samples. As the standards continue to develop, its useful to understand why we are moving away from magnification.

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