Follow the light.

A clear view of an ideal lens

This is a finite-conjugate equivalent-lens teaching model, not a cutaway of a particular commercial microscope. The cutaway housing, adjustment ring and separating covers are illustrative mechanisms, not manufacturer-calibrated parts. The aperture remains an ideal circular stop. Exploding the housing changes the presentation; the equivalent powered plane stays fixed. Infinity-corrected microscopes use an objective and a tube lens.

The synthetic specimen has absorbing patterns in three layers at −12, 0, +12 µm. The fine Ring has a 7.4 µm centreline diameter and two dots 1.6 µm apart. The coarse Frame has a 10 µm centreline side and Gaussian stroke width σ=0.70 µm (1.65 µm full width at half maximum). Its open centre is approximately 8.35 µm wide at half contrast. These feature scales and the 24 µm Ring-to-Frame separation make both sides of the aperture trade-off observable. Focus changes the specimen's position relative to the fixed lens and sensor. The wheel and carriage illustrate that coupling; their rotation and travel are exaggerated and are not calibrated instrument turns. The marked spot is an interface annotation, not a feature added to the specimen. Gold paths trace the geometry of light transmitted through a selected location; they do not show emitted light or the transmitted brightness of that location. Dark patterns transmit less light. The gold circle on the sensor outlines the chosen point’s geometric ray footprint; it is not a diffraction contour. Coloured layer frames are annotations. The overview enlarges the specimen, pupil and sensor independently, and exaggerates axial displacement. It illustrates connectivity and convergence, not measured ray angles or instrument dimensions.

For an equivalent lens with focal length f=4 mm and specimen distance u=4.4 mm at reference focus, the geometric image distance is v=fu/(u−f)=44 mm. The sensor is fixed there. At other depths, the ray centroid at the sensor uses magnification −44/u. The specimen reference and image use x right and y up: the negative sign inverts both coordinates. Display software can reorient real camera images. The 4.4 mm specimen focus plane is different from the lens's 4 mm front focal plane.

The effective objective NA is an ideal pupil stop in air, not the condenser aperture. Many real objectives have a fixed NA. This model assumes a filled pupil and incoherent intensity imaging; changing a real condenser aperture can also change contrast and defocus appearance. Wavelength is 550 nm. Diffraction depth reference λ/NA² is not a sharp visibility boundary: defocused layers still contribute blurred contrast.

The image combines absorption masks convolved with energy-normalized Gaussian kernels. A finite diffraction width is combined with the variance of the geometric ray footprint. This hybrid approximation illustrates blur; it does not reproduce a full wave-optical point-spread function, Airy rings, phase, aberrations, inter-layer shadowing, multiple scattering or noise. Illumination is normalized to isolate spatial effects, so aperture does not change overall brightness here.

Ray motion is a slow visual trace, not the speed of light. The depth colours identify annotations, not biological stains. This exploration does not certify microscopy skill.

• Nikon MicroscopyU · Numerical aperture
• Nikon MicroscopyU · Depth of field and depth of focus
• Nikon MicroscopyU · Infinity optical systems
• Edmund Optics · Lens magnification
• Zhang et al. · Gaussian PSF approximations

Sources support the principles, not validation or endorsement of this model.