Depth of Field in Cinema: The Complete Practical Guide

The Question Every First AC Dreads

You're on set at call time. The DP has chosen an 85mm T1.4 on the ARRI ALEXA Mini LF, and the first shot of the day is a tight two-shot where both actors need to hold focus simultaneously. Your 1st AC turns and asks: how close can the actors stand before the far one goes soft?

Get it wrong and you're either pulling focus on a razor's edge for the entire scene, or stopping down two stops and going back to the gaffer for an hour while the light changes. Neither option looks good at 6:00 AM on a 12-day shoot.

This post explains exactly how depth of field is calculated, what changes it, and how to use the numbers to make confident decisions before the camera rolls.

The calculations here are based on the hyperfocal distance equation used by focus pullers and lens manufacturers, the same formula documented in the ASC Manual, 10th Edition.

How Depth of Field Actually Works

Depth of field is not a fixed property of a lens. It's the byproduct of a formula involving four variables: aperture, focal length, subject distance, and the circle of confusion value for the sensor you're using.

The circle of confusion (CoC) is the maximum diameter a point of light can spread to before it registers as visually out of focus to a viewer. It's not a single universal number. It changes with sensor size because a larger sensor requires less enlargement for the same display size, meaning each pixel covers more physical area.

The standard calculation for CoC is:

CoC = Sensor Diagonal / 1500

For a Full Frame sensor (43.3mm diagonal), CoC = 0.029mm. For Super 35 (31.1mm diagonal), CoC = 0.021mm. For Micro Four Thirds (21.6mm diagonal), CoC = 0.015mm. These differences feed directly into every depth of field calculation you run.

The hyperfocal distance formula is:

H = (f² / (N × CoC)) + f

Where f is focal length in mm, N is the f-stop number, and CoC is in mm. At any focus distance d, near limit = (H × d) / (H + d) and far limit = (H × d) / (H - d) when d is less than H.

Here's a worked example with numbers a 1st AC would use on the day: Sony FX3 (Full Frame, CoC = 0.029mm), 85mm lens at f/2.8, focused at 10 feet (3.05m).

Hyperfocal distance H = (85² / (2.8 × 0.029)) = 7225 / 0.0812 = 88,978mm = 89m. Near limit = (89 × 3.05) / (89 + 3.05) = 271.45 / 92.05 = 2.95m. Far limit = (89 × 3.05) / (89 - 3.05) = 271.45 / 85.95 = 3.16m. Total DoF = 3.16 - 2.95 = 0.21m, or roughly 8 inches.

That 8-inch window means both actors need to stay within 4 inches of each other in depth, not side-to-side spacing, to remain sharp simultaneously.

Three Real-World Examples

Example 1: Narrative Close-Up, Sony FX3

A 5-day narrative short shooting on the Sony FX3 (Full Frame). The DP chose an 85mm f/1.4 for a critical dialogue close-up at 8 feet, wanting maximum background separation. At Full Frame, 85mm, f/1.4, 8 feet: total DoF is approximately 5.8 inches. The 1st AC ran the numbers with the Depth of Field Calculator before the shot. The result meant holding two actors within 2.9 inches in depth during a no-rehearsal run-and-gun setup. The DP switched to 50mm f/2.8 (DoF = 18 inches) and achieved equivalent background separation by moving the camera back, letting the longer distance compress the background naturally.

Example 2: Documentary Run-and-Gun, Canon EOS R5

A one-person documentary crew using the Canon EOS R5 (Full Frame) and a 24mm f/1.8 prime, shooting observational-style interviews in low-light practicals where stopping down wasn't an option. At Full Frame, 24mm, f/1.8, 6 feet: total DoF is 3.1 feet. That window is wide enough to hold a seated subject with minor forward-back movement without a focus pull. The operator confirmed the wide prime was the right call and stopped worrying about soft focus, concentrating instead on framing and anticipating movement.

Example 3: Commercial Product Shot, Blackmagic Pocket Cinema Camera 4K

A commercial director shooting a product hero shot on the Blackmagic Pocket Cinema Camera 4K (Micro Four Thirds) with a 100mm macro lens at f/5.6, subject at 2 feet. The Micro Four Thirds CoC of 0.015mm tightens the DoF further: result was 0.4 inches total. The product's label was sharp while the logo on the cap was already soft at that distance. The director moved the subject to 3.5 feet and opened to f/4, bringing DoF to 1.1 inches, enough to hold the full label sharp while the background fell out of focus cleanly.

Sensor Format Comparison

The table below shows how CoC values differ across the formats most commonly used in indie and commercial production. The CoC directly sets the denominator in the DoF formula, so smaller CoC values produce shallower depth of field at equivalent settings.

The most important takeaway from this table: a Micro Four Thirds camera at f/2.8 produces more depth of field than a Full Frame camera at f/2.8 with an equivalent field of view. Photographers who carry this assumption from stills into cinema regularly make the wrong focus-pulling decisions on mirrorless-based shoots.

How to Use This on Set: A Step-by-Step Process

Step 1: Before the shoot day, identify your sensor format and confirm the CoC value. If you're using the Depth of Field Calculator, this is selected from a dropdown and calculated automatically.

Step 2: For each critical shot in the shot list, note the intended focal length, aperture, and approximate subject distance. These three values are your inputs.

Step 3: Run the DoF calculation and note the near limit, far limit, and total DoF. For two-person scenes, the usable DoF is the window both subjects must stay within.

Step 4: If the DoF is tighter than the blocking allows, evaluate two options: stop down one stop (which doubles DoF approximately) or widen the focal length and move the camera back to maintain framing. Each has tradeoffs for perspective compression and background separation.

Step 5: For hyperfocal shooting on documentary or run-and-gun, calculate the hyperfocal distance for your lens and aperture combination. Focused at H, everything from H/2 to infinity is acceptably sharp. This is the foundational technique for news, documentary, and ENG shooting where manual focus pulling isn't possible.

Step 6: On an anamorphic lens, apply the squeeze ratio before comparing DoF results. A 1.5x squeeze adapter changes the effective horizontal field of view, and most standard DoF calculators assume spherical lenses. Check the Anamorphic Desqueeze Calculator to model actual anamorphic DoF before the shoot.

Pro Tips and Common Mistakes

Pro Tip: At distances beyond hyperfocal distance, the far limit of depth of field extends to optical infinity. For landscape and wide-establishing shots, focusing at 60-70% of hyperfocal distance puts the near limit at roughly half the hyperfocal distance and the far limit at infinity, which is more useful than focusing directly at H where the near limit is H/2 and nothing closer is sharp.

Pro Tip: Lens breathing changes the effective focal length as you rack focus, which shifts DoF mid-shot. Modern cinema lenses are designed to minimize breathing, but vintage and photo-adapted glass can breathe significantly. This matters on close-up rack-focus transitions where the background separation changes visibly during the pull.

Pro Tip: T-stops and f-stops are not interchangeable in DoF calculations. T-stops measure light transmission through the glass, accounting for lens flare and internal reflections. DoF calculations use the f-stop (aperture ratio), not the T-stop. On a T1.5 lens with a geometric aperture of f/1.4, use f/1.4 in your DoF formula.

Common Mistake: Assuming a Full Frame camera always produces shallower DoF than a Super 35 camera at the same focal length and aperture. The comparison depends entirely on whether the field of view is matched. At matched field of view (which requires a longer focal length on Full Frame), Full Frame produces shallower DoF. At identical focal lengths without matching the field of view, the comparison reverses at close distances.

The fix: Always specify whether you're comparing at matched FoV or at matched focal length. Use the Lens Comparison Tool to model equivalent focal lengths across sensor sizes before making the comparison.

Common Mistake: Entering the T-stop value instead of the f-stop into depth of field calculators. A T1.5 cinema lens will give you the DoF of f/1.4 glass, not f/1.5 glass. The difference is small but compounds when you're working at the edge of focus tolerance.

The fix: Look up the lens's geometric aperture ratio (usually listed in the lens specs as the maximum f-stop, separate from the T-stop) and use that value in any DoF calculation.

Frequently Asked Questions

Does sensor size affect depth of field directly?

Yes, but not in the way most people describe it. Sensor size changes depth of field because it changes the circle of confusion value used in the formula. A Micro Four Thirds sensor has a smaller CoC than a Full Frame sensor, which means an MFT camera at f/2.8 produces more depth of field than a Full Frame camera at f/2.8 with an equivalent field of view. The physics isn't that the sensor "sees" differently -- it's that a larger sensor requires less enlargement to reach the same display size, so a larger blur circle still looks sharp.

What's the practical difference between hyperfocal distance and infinity focus?

At infinity focus, your near limit of acceptable sharpness is approximately H/2 (half the hyperfocal distance). At hyperfocal focus, your near limit is H/2 and your far limit extends to optical infinity. Focusing at infinity on a wide lens wastes the near-field sharpness that hyperfocal focus captures. For landscape, establishing shots, or any scene where subjects span a range of distances, hyperfocal focus gives you more usable depth of field than infinity focus at the same aperture.

Why does background bokeh look different on anamorphic lenses?

Anamorphic lenses produce oval bokeh because the front element is cylindrically distorted along one axis. The out-of-focus blur circles are squeezed horizontally, creating the characteristic oval or elliptical bokeh shapes. The degree of oval-ness depends on the squeeze ratio: a 2x anamorphic produces more pronounced oval bokeh than a 1.5x adapter. The DoF itself isn't fundamentally different from a spherical lens at equivalent settings, but the aesthetic rendering of the out-of-focus areas is visually distinct.

Can you use depth of field creatively to direct attention in a frame?

Shallow DoF is the most common attention-directing technique in narrative cinema precisely because the human visual system fixates on sharp regions within a frame. A 2-inch DoF on a close-up at T1.4 means one eye is sharp and the other is slightly soft, which reads as intimacy and isolation. Documentary DPs often prefer 3-5 feet of DoF to maintain subject sharpness during unpredictable movement while still separating the subject from the background cleanly.

How do ND filters affect depth of field?

ND filters don't change depth of field directly. They reduce light transmission, which allows you to maintain a wider aperture in bright conditions without overexposing. The aperture you maintain with an ND filter is what determines DoF. A 6-stop ND filter in full sun lets you shoot at f/2.8 instead of f/22, giving you the DoF of f/2.8 rather than f/22. The Exposure Calculator handles ND filter math alongside aperture and shutter speed calculations.

What is focus breathing and when does it matter?

Focus breathing is the change in effective focal length that occurs as a lens is racked through its focus range. On a 50mm lens with significant breathing, the frame appears to zoom in slightly when you focus close and zoom out when you focus to infinity. This matters on rack-focus shots where the composition changes as focus shifts. Cinema-spec lenses (Zeiss Master Primes, Leica Summilux-C, ARRI/Zeiss Ultra Primes) are designed with minimal breathing for this reason.

Related Tools

The Depth of Field Calculator at the top of this page runs all the calculations in this post in seconds. Enter your sensor format, focal length, aperture, and subject distance to get near limit, far limit, total DoF, and hyperfocal distance.

For decisions about equivalent focal lengths across sensor formats, the Camera Sensor Crop Calculator and Lens Comparison Tool let you model how a lens on one system translates to another. The Anamorphic Desqueeze Calculator handles the squeeze-ratio math for anamorphic DoF comparisons.

For more on how sensor format interacts with the full optical system, Crop Factor Explained for Filmmakers and Shooting Anamorphic on a Budget both build directly on the CoC concepts covered here.

The One Number That Changes Everything

Depth of field is ultimately a creative decision built on optical fact. The math doesn't tell you what aperture to use -- it tells you what aperture choice means for your subject, your frame, and your focus puller's workload. Knowing the numbers means you can choose your DoF intentionally rather than accepting it by default.

This guide focuses on single-camera setups with prime and zoom lenses. Multi-camera DoF matching, where two cameras on different sensor formats must render the same scene with consistent depth of field, is a separate topic worth its own dedicated guide.

If you've pulled focus on a T1.4 or faster at distances under 6 feet, what's the tightest DoF you've successfully held on a handheld setup -- and did you make it work or end up adjusting the shot?