Numerical aperture converter
Convert numerical aperture into what it actually buys: resolution, collection angle and depth of field.
That's about the same as a 40× objective. It can separate detail down to about 423.1 nm.
What it means
How fine can it see?
Resolution figures use green light at 550 nm and the Abbe limit. Shorter wavelengths resolve finer, which is why electron microscopes exist.
Every unit
Your aperture in every unit
Learn
Three things worth knowing
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Resolution = λ ÷ 2NA
At 550 nm, a 0.25 NA objective resolves 1.1 µm and a 1.4 NA oil objective 200 nm. Doubling the NA halves the detail you can separate.
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Abbe, in Jena
Ernst Abbe worked out in 1873 that resolution has a hard limit set by diffraction, not by lens quality. It is carved on his memorial.
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Magnification is not resolution
A 1000× image from a 0.25 NA lens shows no more detail than a 250× one — just bigger, blurrier pixels. NA sets what is there to see.
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Background
About numerical aperture
NA is the sine of the half-angle of light an objective collects, times the refractive index of what is between lens and sample. It decides resolution: the finest detail is about λ ÷ 2NA, which for green light and a 1.4 NA oil lens is 200 nm.
It cannot exceed the refractive index of the medium, which is why oil immersion exists at all: air caps you at 1.0, oil allows 1.5.