Split Focus: Where to Focus for Two Subjects

Updated October 2026

Two people at different distances, one focus plane: the exact focus point, the stop that holds them both, charts for common lenses, and what to do when the stop you need is out of reach.

8 min readIntermediate

Split Focus
Depth of Field
1st AC

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Two subjects, one focus plane

A two-shot with the actors at different distances, a product in the foreground and a face behind it, an over-the-shoulder where the director wants both sharp: the lens has one focus plane, so the only way to hold both is to place the depth of field so its near limit lands on one subject and its far limit on the other. That is a split.

Two numbers come out of it: where to set the focus, and the stop that stretches the depth of field over the gap. Both have exact answers from the depth of field formulas.

Where to focus

Split focus point

s = 2 × near × far ÷ (near + far)

The harmonic mean of the two distances. It is exact for the thin-lens limits, whatever the lens and stop, and it always falls nearer the close subject than the halfway point.

Where

near: Distance to the nearer subject(m or ft)
far: Distance to the farther subject(m or ft)

Example: Subjects at 2m and 3m (or 6 ft and 10 ft)

Calculation:: 2 × 2 × 3 ÷ (2 + 3) = 2.4m | 2 × 6 × 10 ÷ (6 + 10) = 7.5 ft
Result:: Focus at 2.4m (7′10″), or 7′6″ for the feet example

Why the harmonic mean: depth of field is symmetrical in 1 ÷ distance. The near limit sits as far in front of the focus point, measured in 1 ÷ distance, as the far limit sits behind it. So the focus point is the average of 1 ÷ near and 1 ÷ far, turned back into a distance. The Split focus mode of the free depth of field calculator works it out in feet or meters.

The stop you need

Stop to hold both subjects

N = f² × (far − near) ÷ (2 × c × near × far) × s ÷ (s − f)

All lengths in millimeters. The last factor, s ÷ (s − f), is within a few percent of 1 at normal distances; drop it for a quick figure. Round the result toward the next deeper stop.

Where

f: Focal length(mm)
near, far: Subject distances(mm)
c: Circle of confusion(mm)
s: The split focus point(mm)

Example: 50mm on Super 35 (c = 0.025mm), subjects at 2m and 3m

Calculation:: 2,500 × 1,000 ÷ (2 × 0.025 × 2,000 × 3,000) × 2,400 ÷ 2,350 = 8.5
Result:: T8.5: focused at 2.4m, T8 holds 2.02m to 2.96m; T11 holds 1.91m to 3.24m

The (far − near) ÷ (near × far) term is 1 ÷ near − 1 ÷ far: what matters is how far apart the subjects are in 1 ÷ distance, not in meters. One meter of separation at 2m and 3m needs T8.5 on a 50mm; the same meter at 4m and 5m needs much less. And the stop goes with the square of the focal length, so a wider lens is the strongest lever you have. The free depth of field calculator gives this exact stop in its Split focus mode.

The one-third rule

The rule of thumb says to focus a third of the way from the near subject to the far one. That point equals the harmonic mean only when the far subject is exactly twice as far as the near one. Otherwise it is off, and off in the expensive direction when the subjects are far apart.

Super 35, c = 0.025mm. Stop needed when focused at each point.

Subjects, lens	Harmonic mean	Stop	One-third point	Stop
2m & 4m, 35mm	2.67m	T6.2	2.67m	T6.2
1m & 3m, 35mm	1.50m	T16.7	1.67m	T20.0
2m & 10m, 25mm	3.33m	T5.0	4.67m	T7.2

With 2m and 10m, focusing at the third asks for T7.2 instead of T5, about a stop for nothing.

Split focus charts

The focus point and the stop that holds both subjects on Super 35 (c = 0.025mm). For full frame at 0.030mm, the same lens needs about a sixth less stop number. Anything past T22 is out of reach for most cine lenses.

In meters

Focus point (harmonic mean) and exact stop needed, Super 35.

Subjects	Focus at	25mm	35mm	50mm	75mm
1m & 1.5m	1.20m (3′11″)	T4.3	T8.4	T17.4	T40
1.5m & 2.5m	1.88m (6′2″)	T3.4	T6.7	T13.7	T31
2m & 3m	2.40m (7′10″)	T2.1	T4.1	T8.5	T19.4
2m & 4m	2.67m (8′9″)	T3.2	T6.2	T12.7	T29
3m & 5m	3.75m (12′4″)	T1.7	T3.3	T6.8	T15.3
4m & 8m	5.33m (17′6″)	T1.6	T3.1	T6.3	T14.3
2m & 10m	3.33m (10′11″)	T5.0	T9.9	T20.3	T46

In feet

Focus point (harmonic mean) and exact stop needed, Super 35.

Subjects	Focus at	25mm	35mm	50mm	75mm
4 ft & 6 ft	4′10″	T3.5	T6.9	T14.2	T32
5 ft & 8 ft	6′2″	T3.1	T6.1	T12.6	T29
6 ft & 10 ft	7′6″	T2.8	T5.4	T11.2	T25
8 ft & 12 ft	9′7″	T1.7	T3.4	T7.0	T15.8
8 ft & 15 ft	10′5″	T2.4	T4.7	T9.7	T22
10 ft & 20 ft	13′4″	T2.1	T4.1	T8.3	T18.8

When the stop is too deep

Often the answer is a stop the lighting can't support or the DP doesn't want. The options, roughly in the order a camera team tries them:

Go wider from the same spot. The stop scales with the focal length squared: at 2m and 3m, a 50mm needs T8.5 and a 35mm T4.1.
Restage in depth. Bringing the far actor from 4m to 3m takes a 50mm from T12.7 to T8.5.
Buy the stop. More light, a higher ISO or less ND. Each extra stop of light lets you close down one stop; the exposure triangle guide covers the trade, and the Exposure calculator keeps the trade-offs straight.
Use a split diopter. A half-moon close-up lens over part of the frame brings the near subject into focus while the rest of the lens holds the far one. It leaves a soft transition line that has to fall on something plain. The close focus guide covers diopter strengths.
Rack instead of split. If the scene allows, favor whoever is talking and pull between them. A rack you plan is better than a split that is soft on both.

Split mode in CineMath

CineMath's Depth of Field calculator has a Split mode: enter the near and far distances in feet or meters, the focal length and the format, and it gives the focus point and the stop to hold both. It warns when the stop needed is past f/22.

The free web version of the calculator uses the exact formula above for the stop.

Questions

Where do you focus to get two subjects sharp?

At the harmonic mean of their distances: 2 × near × far ÷ (near + far). For subjects at 2m and 3m that is 2.4m; for 6 ft and 10 ft it is 7 ft 6 in. It always sits nearer the close subject than the halfway point.

What stop do I need to hold two subjects in focus?

N = f² × (far − near) ÷ (2 × c × near × far), with everything in millimeters (add the factor s ÷ (s − f) for the exact figure). A 50mm on Super 35 (c = 0.025mm) holding 2m and 3m needs about T8.5.

Is it true you should focus one-third of the way between two subjects?

It is exactly right only when the far subject is twice as far as the near one. When they are closer together in depth, the right point is nearer the middle; when they are farther apart, it is closer to the near subject. For 2m and 10m the third-of-the-way point is 4.67m, while the right point is 3.33m, and focusing at the third costs about a stop.

What if the stop needed is too deep?

Get more light or ISO to reach the stop, go to a wider lens from the same position (halving the focal length quarters the stop number needed), bring the subjects closer together in depth, use a split diopter, or rack focus between them instead of holding both.

Next step: plan your next two-shot before the rehearsal. Put the marks into CineMath's Split mode for the focus point, and check the stop against the chart above or in the free depth of field calculator.