MY SIMULATOR

English Bellows Camera Simulator

Find the focus. Capture the light.

INTERACTIVE 3D

Ground glass (upside down)

Virtual demonstration of optics — no chemicals, no real darkroom instructions. Values are model values.

Focus

Aperturef/8

Exposure1/60 s

Lab & science

Drag to orbit, wheel / pinch to zoom, tap the camera parts. Space = take photograph, R = reset, [ ] = focus, arrows = aperture / exposure.

Setup

Light on the subject (scene EV at ISO 100)

Plate speed (ISO)

Print style

Camera

Graphics (High on every device; Low = smaller ground-glass render)

Live readout (model values)

Missions

Mission 5: with the 210 mm lens, how long (mm) must the bellows be to focus a subject 2.4 m away?

The science

What you see

A field camera in a Victorian parlour. The lens forms an upside-down image on the ground glass. Racking the bellows changes the lens-to-plate distance v; that is how you focus. The iris sets the f-number, the shutter sets the time. The plate records the light with an S-shaped response.

Equations

Thin lens          1/f = 1/u + 1/v        f = 210 mm
Blur circle        c = (f/N) |v_s - v(u)| / v(u)
Diffraction        d = 2.44 lambda N v_s / f   (lambda 550 nm)
Total blur         b = sqrt(c^2 + d^2 + a^2),  a = 9/N^3 mm [model]
Hyperfocal         H = f^2/(N c0) + f ,  c0 = 0.15 mm
Near / far limit   u(H-f)/(H+u-2f) ,  u(H-f)/(H-u)
Exposure value     EV = log2(N^2 / t)    (ISO 100)
Stops over         log2(t_eff/N^2) + EV_scene + log2(ISO/100) - 2 log2(v/f)
Bellows factor     (v/f)^2   (light lost when racked out)
Reciprocity        t_eff = t^0.9 for t > 1 s [model]
Plate response     y = E^n / (E^n + 0.18^n)   (S-curve, n = 1.3)
Vignetting         cos^4(theta)
Pendulum           theta'' = -(g/L) sin(theta),  T = 2 pi sqrt(L/g) (1 + theta0^2/16)
Motion blur        b = (v/u) speed t

Assumptions & honest simplifications

The photograph is rendered by a gather depth-of-field filter with the thin-lens blur circle for every pixel, then a film curve; real lenses add aberrations and bokeh shapes not modelled here.
Scene exposure is calibrated so that the average of the room is 18% grey at 0 stops. Light level is a setting, not a physical simulation of the window.
Motion blur averages up to 24 sub-frames over the exposure; the pendulum is a small-angle model.
No chemistry, development times or darkroom steps are modelled or taught.

Independent numerical checks

Also in node: node check.js (bisection DoF limits, RK4 pendulum, sunny-16).

Sources

Standard geometric-optics treatments of the thin lens, circle of confusion and hyperfocal distance; the sunny-16 rule; Airy diffraction limit; photographic H&D characteristic curve (concept). Constants are model values [verify before real use]. No brand or camera maker is depicted.

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