What Circle of Confusion Should You Use for Your Camera?

The Number Your DoF Calculator Is Waiting For

You open the Depth of Field Calculator, enter focal length, aperture, and subject distance. There is one field that trips up almost every operator the first time: circle of confusion. The calculator asks for a value in millimetres. You are on a Sony FX3 shooting at 4K Full Frame. The dropdown offers "Full Frame (35mm)" at 0.029mm and several other options. Which do you pick, and why does it matter?

The wrong CoC value can shift your calculated depth of field by a factor of almost two. On a T1.4 lens at 8 feet, using a CoC of 0.030mm instead of 0.019mm tells you that your DoF is 7.4 inches when it is actually 4.8 inches. That difference puts a second actor outside your actual sharp zone while the calculator says they are inside it.

This post explains what circle of confusion is, how the correct value is derived for every sensor format, and which number to enter for the most common cinema and mirrorless cameras in use today.

The values here are derived from the standard CoC formula in the ASC Manual and lens manufacturer depth of field charts: CoC equals sensor diagonal divided by 1500, based on a 25cm viewing distance and an 8x10 print enlargement factor.

What Circle of Confusion Actually Is

Circle of confusion is not a camera setting. It is a threshold value: the maximum diameter of a blurred point of light that still appears acceptably sharp to the human eye at a standard viewing distance and print size. Every depth of field formula uses this threshold to define the near limit and far limit of the sharp zone.

The CoC value scales the entire depth of field calculation. A larger CoC value produces a more generous DoF prediction because the threshold for acceptable sharpness is wider. A smaller CoC narrows the calculated DoF because the sharp zone is defined more strictly. The relationship is roughly linear: doubling the CoC approximately doubles the calculated depth of field at the same aperture and focus distance.

The industry-standard formula for deriving CoC from sensor size is straightforward:

CoC (mm) = sensor diagonal (mm) / 1500

The 1500 divisor comes from an assumed 8x enlargement to a 25 x 30cm print viewed at 25cm. Larger sensors have larger diagonals, which produce larger CoC values and more generous DoF predictions. Smaller sensors produce tighter CoC values and narrower calculated DoF.

Worked example: the Sony FX3 uses a Full Frame sensor measuring 35.9 x 24.0mm. The diagonal is sqrt(35.9 squared plus 24.0 squared) = sqrt(1288.81 + 576.00) = sqrt(1864.81) = 43.2mm. Divide by 1500: 43.2 / 1500 = 0.0288mm, rounded to 0.029mm.

Three Real-World Examples of CoC Choice on Set

Example 1: Narrative Feature on ARRI ALEXA 35, Super 35 Extraction

A low-budget feature shoots on an ARRI ALEXA 35 in Open Gate mode with a Super 35 extraction. The active image area for that extraction measures 26.67 x 14.99mm, giving a diagonal of 30.6mm. The correct CoC is 30.6 / 1500 = 0.020mm. A 1st AC using the Full Frame value of 0.029mm would calculate roughly 45% more DoF than actually exists on the sensor -- a meaningful error on a T1.4 lens at close subject distances.

Example 2: Documentary on Sony FX9, Switching Between Full Frame and Super 35 Crop

A documentary DP shoots the Sony FX9 in Full Frame 6K mode (35.9 x 24.0mm, CoC = 0.029mm). Mid-shoot they switch to the Super 35 crop (23.5 x 12.7mm) for reach. The CoC drops to approximately 0.018mm -- the effective DoF at any given aperture and distance shrinks by nearly 40%. The DP notes both values in the camera report and confirms with the 1st AC which mode is active before each setup.

Example 3: Corporate Shooter on Blackmagic Pocket Cinema Camera 4K, Micro Four Thirds Mode

A corporate one-person crew works with the Blackmagic Pocket Cinema Camera 4K (17.3 x 13.0mm, CoC = 0.015mm). This produces significantly narrower DoF predictions than a Full Frame camera at the same aperture and distance. At f/2.8 and 6 feet, the Blackmagic returns roughly 16 inches of DoF versus 24 inches on Full Frame. Confirming the correct CoC in the Circle of Confusion Calculator before the shoot avoids false confidence about subject separation on interview setups.

Circle of Confusion Reference by Sensor Format

The table below shows the correct CoC value for common cinema and mirrorless sensor formats. Use these values directly in any DoF calculator.

Full Frame cameras cluster around 0.029mm, Super 35 formats around 0.018 to 0.023mm, and Micro Four Thirds at 0.015mm. When in doubt, calculate from the sensor diagonal rather than accepting a dropdown default.

How to Confirm the Right CoC Before Any Shoot: Step by Step

Step 1: Confirm your camera's active sensor mode before opening any DoF tool. Many cameras offer multiple modes (Full Frame, Super 35 crop, windowed 4K, anamorphic de-squeeze). The active mode determines which sensor dimensions to use. Check the camera's operating manual for the "active image area" in millimetres for each mode.

Step 2: Look up the sensor dimensions (width x height in mm) for your confirmed mode. Use the manufacturer's published active image area, not the full sensor physical size, which is often slightly larger than the recorded area.

Step 3: Calculate the diagonal using: diagonal = sqrt(width squared + height squared). Use a calculator or the Circle of Confusion Calculator, which computes the diagonal and CoC simultaneously from entered dimensions.

Step 4: Divide the diagonal by 1500 to get your CoC in mm. Round to three decimal places: 0.029, not 0.02888.

Step 5: Enter that value into the CoC field of the Depth of Field Calculator. If the calculator has a sensor format dropdown, confirm the entry matches your active mode before running any DoF table for the day's lenses.

At the end of this process you have a verified CoC value confirmed for the specific camera mode in use -- every focus decision for the day then builds on an accurate number.

Pro Tips and Common Mistakes

Pro Tip: When a DoF calculator uses a dropdown rather than a manual CoC field, check whether its "Super 35" entry matches your camera's specific Super 35 variant. ARRI's Super 35 extraction from the ALEXA 35 Open Gate is not the same dimensions as a generic Super 35 designation in older apps. Enter a manual CoC derived from the spec sheet rather than accepting the generic label.

Pro Tip: On anamorphic formats, the CoC calculation uses the squeezed sensor dimensions -- the CoC does not change because you are shooting with an anamorphic lens. The squeeze affects horizontal field of view, not depth of field math. Use the sensor's native dimensions when calculating CoC even when the lens has a 1.3x or 2x squeeze ratio.

Pro Tip: Large Format cameras like the ARRI ALEXA LF produce more background separation at equivalent apertures partly because the larger CoC (0.030mm vs. 0.020mm for Super 35) is itself more generous. But the full LF effect comes from combining that CoC with the longer focal lengths typically required to match Super 35 field of view -- both factors compound the shallow-focus characteristic.

Common Mistake: Not checking the active sensor mode before opening a DoF app. Many Sony FX-series cameras offer Full Frame, Super 35, and APS-C crop modes, and a DoF app does not know which is active unless you confirm it first. The fix: make it part of the pre-shoot checklist, alongside confirming frame rate and codec.

Common Mistake: Assuming all "Full Frame" designations represent the same sensor dimensions. The Canon EOS R5 Full Frame (36.0 x 24.0mm) and the Sony VENICE 2 Full Frame (35.9 x 24.0mm) produce essentially the same CoC. But a "Full Frame" extraction from an Open Gate camera at a non-standard crop ratio may have a different active area. Confirm sensor dimensions from the manufacturer spec sheet rather than assuming the label is sufficient.

Frequently Asked Questions

What happens if I enter the wrong circle of confusion value in a DoF calculator?

Your near and far focus limits will be inaccurate, and any hyperfocal distance calculations derived from the same CoC will be equally wrong. The error is roughly proportional to the CoC mismatch: using a CoC 30% too large produces a DoF estimate approximately 30% more generous than reality. On a T1.4 lens at close distances, that gap is the difference between both performers holding focus and the far one going soft.

Why do different DoF apps show different values for the same setup?

The most common reason is different default CoC values for the same sensor label. One app may use 0.025mm for "Super 35," another may use 0.019mm -- both are technically defensible depending on the assumed viewing conditions. Entering a manual CoC derived from your camera's spec sheet eliminates this variability and gives you a consistent, verifiable result across any app.

Does changing frame rate affect circle of confusion?

No. Frame rate does not alter sensor dimensions or CoC. If you switch from 24fps to 48fps on the same camera in the same crop mode, the CoC stays the same. What changes with frame rate is shutter speed (for a given shutter angle) and the character of motion blur -- not depth of field limits for a static focus distance.

Is the CoC in a DoF calculator the same as the circle of least confusion in optical design?

These are distinct concepts that share similar names. Circle of least confusion is an optical design term describing the point where an astigmatic lens produces its smallest spot size -- it is used in lens aberration analysis. The circle of confusion used in DoF calculations is a perceptual threshold based on human vision and viewing conditions, not an optical minimum. The naming overlap is a consistent source of confusion in cinematography education.

Related Tools

The Circle of Confusion Calculator computes the correct CoC for any sensor format from its dimensions, including custom or unusual crops not covered by any dropdown. Use it alongside the Depth of Field Calculator to confirm near and far limits before critical setups. For format conversions and crop factor math across multiple systems, the Camera Sensor Crop Calculator covers the geometry for every major format.

For the full depth of field calculation explained from first principles, Depth of Field in Cinema covers the complete optical math with worked examples. For understanding how sensor size affects these values across cinema formats, Crop Factor Explained for Filmmakers covers every major format conversion in production use.

One Number, Confirmed Before the First Take

The circle of confusion value is the single most underexplored input in any DoF calculator. Enter the wrong one and every near/far limit, hyperfocal distance, and focus depth table you produce from it is off from reality. Take two minutes before the shoot day to confirm your camera's active sensor mode and calculate the correct CoC once. Every focus decision for the day then builds on an accurate foundation.

This post covers standard spherical lenses and single-sensor setups. Anamorphic DoF and multi-camera format matching involve additional considerations worth a separate guide. If you have encountered a focus miss that turned out to be a CoC error in the calculator, what camera mode were you in and how far off was the prediction?