Cine has a gear ratio of 2:1 for cine style lenses,
which means one turn of the focus knob will result
in two turns of the focus gear. This gear ratio is common
to all classic follow focus units from ARRI (FF-3, FF-4, etc.)
and is traditionally suited to cine lenses such as Ultra Primes,
Compact Primes, Alura Zooms, Angenieux Zooms, etc...
HD has a slower gear ratio of 1:1 for 2/3” broadcas
t and still photo lensesIn this case, one turn of the focus knob w
ill result in a single turn of the focus gear. This particul
ar gear ratio might be preferred when using lenses with a short focus
throw, where the scale from minimal focus to infinity is so short that a
traditional 2:1 ratio could be too direct, lacking
in precision. Typical lenses suited to the HD ratio
are modern still prime lenses, some ENG zooms, extreme wide-angle
lenses or some older designs.