Microscope depth of field calculator
DOF = λ·n / NA² + n · pixel / NA
Enter wavelength, numerical aperture and immersion medium: the tool computes depth of field using the Berek convention, showing separately the wave-optical contribution (diffraction) and the one tied to sensor sampling. It also recalls axial resolution, a neighbouring but different quantity, to avoid the most common confusion in the field.
Berek convention: diffraction + sampling. See the "Limits" section below.
Axial resolution (Rayleigh): 803.9 nm
Not to be confused with depth of field: axial resolution describes the ability to separate two planes, depth of field the focus tolerance before blur becomes perceptible.
Scientific dossier
What the tool computes, what it assumes, where it stops being valid, and where its data comes from.
Method & formulasDOF = λ·n / NA² + n · pixel / NA
DOF = λ·n / NA² + n · pixel / NA
diffraction (wave-optical) + sampling (detector)
The first term depends only on the optics. The second depends on the sensor: it is the pixel size referred back to the specimen. Showing them separately makes a counter-intuitive fact visible, a coarser sensor increases apparent depth of field, with no optical gain whatsoever.
- Depth of field
- · thickness of specimen that appears sharp at a given focus setting. It is a focus tolerance.
- Axial resolution
- · smallest separable distance along the optical axis. It is a separation capability, not a tolerance. Both quantities share the same unit and order of magnitude, but answer different questions.
- Diffraction contribution
- · purely wave-optical term, λ·n / NA². It depends on no detector and falls very fast as numerical aperture increases.
- Sampling contribution
- · detector-related term, n · pixel / NA. A coarser pixel does not reveal the blur: depth of field then appears larger.
Validity domainDepth of field has no single definition: it depends on the blur acceptability criterion chosen.
Depth of field has no single definition: it depends on the blur acceptability criterion chosen. This tool applies the Berek convention, which sums a wave-optical contribution and a detector-related one. Other definitions exist, some keeping only the diffraction term: they then give a smaller value without being wrong. Any value shown here is a design estimate, never a measurement: perceived sharpness also depends on specimen contrast and signal-to-noise ratio.
Effect of numerical apertureDepth of field varies as the inverse square of numerical aperture: moving from an NA 0.
Depth of field varies as the inverse square of numerical aperture: moving from an NA 0.3 objective to an NA 1.4 one reduces it by more than a factor of twenty. This is why a high-aperture immersion objective demands such precise focus, and why z-stack acquisition becomes essential on thick specimens.