Is f/2.8 shallow or deep?

It sits between the two. A standing figure holds sharp, and the background softens without disappearing, so it reads as neither Shallow Focus nor Deep Focus.

What is the difference between f/2.8 and f/4?

One stop of light and a visible amount of depth. At f/4 a person in the middle distance is recognisable. At f/2.8 they are a soft shape.

How do I prompt f/2.8?

Name the stop, say the subject is sharp, and say the background is soft but still readable as a place. Name one object in it so the model keeps it.

f/2.8

f 2.8
T2.8

Separates the subject and still lets the background read as a place.

Run this shot

Opens a video model with the prompt in it. The price is on the page before you sign in.

What it is for

f/2.8 separates a subject from a background without deleting it. The person comes forward and the room stays a room.

It is also the stop most professional zooms hold across their whole range, so a lot of documentary and news footage looks exactly like this.

How it works

The sharp band is deep enough for a standing figure on a normal lens, so a full length shot holds from shoes to hair.

Most lenses are close to their best here. Corner sharpness has arrived, contrast is up, and diffraction is still far away.

Light drops to a quarter of what f/1.4 passes. An interior needs a lamp of its own rather than the practicals alone.

When to use it

Use it for a two shot, for a walking subject, and for any scene where the audience needs to know where they are.

Skip it when the background is ugly or busy. At f/2.8 enough of it survives to distract.

Told apart from its neighbours

f/1.8 turns the same background into tone. f/2.8 keeps its shapes, so a window stays a window.

f/4 goes further again and brings the middle distance back. The test is whether a person standing three metres behind the subject is recognisable: at f/2.8 they are a shape, at f/4 they are a person.

On film

News and documentary crews live at this stop, because a constant f/2.8 zoom holds the same exposure from wide to long. The look follows the equipment: soft enough to lift a face out, deep enough to keep the street behind it.

The prompt

Replace the blanks, keep the rest. Then run it on a video model.

<subject> shot at f/2.8, subject sharp head to toe, background soft but still readable as a room, moderate depth of field

Run it

What goes wrong

The model reads it as a blur request and dissolves the room. Say the background stays readable and name one thing in it.

The other failure is a flat frame with nothing separated. Ask for the subject sharp and the background soft in the same line.

Leave out

everything sharp to the horizon, fully dissolved background

Watch for

The stop that keeps the location. Say the background is soft but named.

Questions

Documentary, interviews and any shot that has to separate a subject while keeping the location readable. It is also the widest stop most professional zooms hold.