Microscope Resolution


Microscope resolution depends on the wavelength of light (λ) and the numerical aperture of the objective lens (NA). Use 550 nm for white light.


Lateral resolution = 0.61 λ / NA Objective


or if you include the condenser:    Lateral resolution = 1.22 λ / (NA Objective + NA Condenser)


Depth (Z) resolution  = 2 λ / NA squared


NA (numerical aperture) is a measure of the ability of the lens to gather light from a wide solid angle.


NA = n. Sin(α)


n = refractive index of immersion medium (air = 1, oil = 1.5, glycerine = 1.5, water = 1.3)

α = half the solid angle of light gathered by the lens (max  90 deg)


Cameras and Pixels


Image pixel size depends on the camera, C mount and objective lens: 


Image pixel size = CPS / (Mag * CM)

Camera field of view = (CPS * NPix) / (Mag * CM)


CPS = camera pixel size (typically 2 μm – 7 μm)

NPix = camera number of pixels in X and Y dimensions

Mag = objective lens magnification

CM = C mount magnification (typically 0.4x – 1x)




Field of view = Eyepiece Field Number (mm) / Objective Magnification


Camera Sampling


This graph shows you if the camera is over sampling or under sampling the microscope image. For example, if you are using an objective with a NA of 0.8 then the pixel size must be 0.2 microns or smaller. This can typically be achieved for a 20x objective with a 1.4 MPixel camera, i.e. it is surprising how few camera pixels are required to correctly sample the microscope image.