Microscope depth of field calculator

Wavelength, numerical aperture and immersion medium give the depth of field using the Berek convention, with its two contributions shown separately: diffraction and sensor sampling. The axial resolution is given alongside.

The first term depends only on the optics; the second depends on the sensor, through the pixel size referred back to the specimen.

Depth of field

thickness of specimen that is sharp at a given focus setting; a focus tolerance.

Axial resolution

smallest separable distance along the optical axis; a separation capability, not a tolerance. Both quantities share the same unit and order of magnitude.

Diffraction contribution

wave-optical term, λ·n / NA², independent of the detector. It falls fast as numerical aperture increases.

Sampling contribution

detector-related term, n · pixel / NA. A coarser pixel does not reveal the blur: depth of field appears larger, with no optical gain.

Depth of field has no single definition: it depends on the chosen blur criterion. The Berek convention sums a wave-optical contribution and a detector contribution; other definitions keep only the diffraction term and give a smaller value. The value shown is a design estimate, not a measurement; perceived sharpness also depends on specimen contrast and signal-to-noise ratio.

Depth of field varies as the inverse square of numerical aperture: from NA 0.3 to NA 1.4, it drops by more than a factor of twenty. With a high-aperture immersion objective, a thick specimen requires a z-stack.