Circular calibration chart with concentric rings and angular markings used for lens alignment and focus measurement on set.
Technical Details
Professional marking disks are made of matte aluminum or plastic with laser-accurate markings. The standard version features concentric circles at 5 cm intervals, angle markings from 0° to 360° in 15° increments, and checkerboard patterns with 2x2 cm squares for focus measurement. High-precision versions achieve tolerances of ±0.1 mm. Special versions include gray cards according to DIN 5033 with 18% reflectance, color patches according to Macbeth ColorChecker standard, or LED lighting for low-light calibration.
History & Development
Arri developed the first standardized marking disk in 1963 for the new generation of Cooke series zoom lenses. Previously, cinematographers used improvised reference objects such as watches or self-made circle templates. In 1978, Panavision introduced temperature-compensated disks that account for thermal expansion of lenses. Since 1995, digital test patterns on monitors have supplemented physical disks but have not completely replaced them, as spatial depth staging can only be measured with physical objects.
Practical Use in Film
In "Blade Runner 2049" (2017), DoP Roger Deakins used marking disks for precision calibration of the ALEXA 65 cameras for extreme macro shots of Harrison Ford's eyes. Steadicam operators use 30 cm disks as standard before shooting begins for balance calibration and lens adjustment. Focus pullers use the disks to calibrate focus marks on follow focus systems – a 50mm lens typically requires a 15° turn on the follow focus ring between infinity and close focus at a distance of 3 meters.
Comparison & Alternatives
While test charts check two-dimensional resolution and color reproduction, the marking disk enables three-dimensional geometric measurement in space. Modern laser rangefinders partially replace them for focus measurements but fail with complex camera movements or lens-whacking techniques. Focus pulling apps on tablets offer digital alternatives but do not achieve the 0.1 mm accuracy of mechanical markings for precision work with long focal lengths from 200mm upwards.