F-Stop

What this is about

Stops are the currency of exposure talk on set. The standard series — 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 — steps in factors of the square root of two, so each full stop doubles or halves the light. When a DP asks for half a stop more fill or an ND that costs three stops, everyone from gaffer to DIT converts instantly. The f-number also anchors depth-of-field tables and lens data sheets, which is why it survives on cine sets even though exposure itself is called in T-stops.

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:

• Smaller number, bigger opening: f/2 lets in sixteen times the light of f/8 — the inversion trips up every newcomer.
• Full stops multiply the f-number by roughly 1.4; thirds of a stop are the fine steps cameras display.
• Stopping down far past f/11 on Super 35 starts costing sharpness to diffraction.

With TillyGen

In the production plan the working stop sits next to each lighting setup, so power and lamp counts are argued from a number, not a feeling.

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.