Presets
Playback
Film, shutter and screen
Each crank turn pulls one frame down while a blade covers the lens; extra blades raise the flash rate without changing the frame rate.
Model checks
The science
What is modelled
A cycloidal claw moves the film one frame pitch (7.62 mm) in part of each turn and then holds it still. A continuously driven sprocket feeds the loop above the gate. A shutter with one to three blades turns once per frame, hiding the pull-down and adding extra flashes to hide flicker.
Equations
- Cycloidal pull-down
s = p (x - sin(2 pi x) / 2 pi), x the fraction of the pull-down angle; peak speed 2 times the mean. - Loop swing: largest gap between claw and sprocket motion, where their speeds are equal,
1 - cos(2 pi x) = pull-down / 360. - Open time
1 - n beta / 360; flash ratefps x n. - Flicker estimate
CFF = 40 + 12.5 log10(L / 55)Hz; reel radiussqrt(r0^2 + t length / pi).
Checks run in the page
- Film feed from the integrated claw speed, in ft/min.
- Peak and end speeds of the cycloid.
- Loop swing against its formula.
- Shutter open fraction and pull-down coverage.
- Flicker threshold and blade count, and reel winding.
Honest simplifications
Rigid parts and a simplified cycloidal claw; the flicker law is a rough Ferry-Porter style estimate for a bright screen, 0.14 mm film and a 25 mm core are typical but assumed, and gate friction, film shrinkage and loop dynamics are not modelled.
What to try
- Press Mistimed shutter: part of the pull-down is visible as a travel ghost.
- Press Silent speed, one blade: 16 flashes a second flicker.
- Press Three blades, brighter screen to see how the flash rate beats the flicker threshold.