Confocal Resolution Calculator
Compare lateral and axial resolution between widefield and confocal microscopy with adjustable pinhole size.
Confocal lateral FWHM
197.2 nm
widefield 202.1 nm
Confocal axial FWHM (point)
418 nm
widefield 523 nm
Optical section FWHM (plane)
518 nm
widefield: no sectioning
Pinhole diameter
28.76 µm
at 60× magnification
Formulas
Widefield: lateral 0.51 λ/NA, axial 0.886 λ/(n − √(n² − NA²))
Confocal, pinhole → 0: lateral 0.37 λ/NA, axial 0.64 λ/(n − √(n² − NA²))
Confocal PSF = illumination PSF × (detection PSF ⊗ pinhole)
Pinhole diameter = AU × 1.22 λ/NA × M
Scalar paraxial theory, equal excitation and emission wavelengths, uniformly filled pupil. At 1 AU the lateral FWHM is within 3 % of widefield: it narrows by about 15 % at 0.7 AU and 22 % at 0.5 AU, at the cost of signal. The axial values are for a point; the optical section is the response to a thin fluorescent plane.
Model and references
Textbook approximation. A standard approximation from the literature (for example paraxial, plane-wave or Gaussian-beam), valid within the range the page states. About the tiers
Scalar paraxial confocal theory with equal excitation and emission wavelengths and a uniformly filled pupil, computed numerically for pinholes of 0–5 AU; the axial scale n − √(n² − NA²) follows Wilhelm. Widefield values are the single Airy and sinc² PSFs.
- Wilson T., Sheppard C. J. R. (1984). Theory and Practice of Scanning Optical Microscopy. Academic Press. Confocal PSF as the product of the illumination PSF and the pinhole-integrated detection PSF.
- Wilson T. (2011). Resolution and optical sectioning in the confocal microscope. J. Microsc. 244, 113–121. Lateral, axial and plane responses against pinhole size. doi:10.1111/j.1365-2818.2011.03549.x
- Wilhelm R., Gröbler B., Gluch M., Heinz H. (2003). Confocal Laser Scanning Microscopy: Principles. Carl Zeiss. Airy units, the 0.37/0.51 λ/NA and 0.64 limits, and the geometric section formula.
- Born M., Wolf E. (2019). Principles of Optics, 7th ed., §8.5.2 and §8.8. Cambridge University Press. Airy pattern, encircled energy and the defocused PSF. doi:10.1017/9781108769914