Cirkut Gear Calculator

The Cirkut camera produces a sharp panoramic image by rotating on a pivot while film advances past a vertical slit. For this to work correctly, the film must move at precisely the right speed relative to the camera's rotation — a relationship determined by the drive gear. Selecting the wrong gear produces an image that is stretched or compressed horizontally, regardless of focus. This calculator determines the correct gear for a given lens and subject distance, based on the geometric relationships for a 1920s-era No. 10 camera.

How to use the calculator

Enter your lens focal length in millimeters and the minimum subject distance you intend to work at. The calculator will return the usable gear range, with each gear's corresponding subject distance, lens extension, and exposure correction factor. Gears are suppressed when they fall outside the camera's physical limits — either exceeding bellows travel or placing the subject closer than your specified minimum. The topmost row, where listed, represents the infinity gear: the largest gear at which the lens can be focused at or near infinity for the focal length entered. Advanced users can adjust camera constants for other Cirkut models using the controls below the main inputs.