Circle of Confusion

What this is about

Every depth-of-field chart, lens scale and focus app silently assumes a circle-of-confusion value — around 0.025mm is a common full-frame convention. Focus pullers care because the assumption sets their tolerance: a chart built for HD viewing is optimistic for a 4K cinema screen, where the same blur circle spans more pixels. When a shot must survive a big screen, experienced ACs treat table depth of field as a maximum and keep focus tighter than the numbers demand.

A term only helps when everyone on set means the same thing by it — so what follows is how it is used, not a dictionary definition.

What runs differently here

In planning terms, that means:

• The value is a viewing convention, not physics — it encodes screen size, resolution and audience distance.
• Higher-resolution delivery shrinks the acceptable circle and with it the real depth of field.
• Two focus apps disagreeing usually means two different circle-of-confusion defaults.

With TillyGen

In the production plan the delivery format sits next to the camera package, so focus tolerances are argued from the screen the film will meet.

Change one constraint and the consequences travel through the whole plan: affected shots are flagged, the call sheet is regenerated, and nobody keeps working from yesterday's version.