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{{ jsonOutput }}Focus has one exact plane, but photographs are judged across a range. Detail just in front of or behind the focus distance may still look sharp because the blur is small enough for the final viewing size. Depth of field names that acceptable-sharpness range, not a hard wall where sharpness suddenly starts or stops.
The judgment depends on the circle of confusion, usually shortened to CoC. A small blur spot on the sensor may still be seen as a point in a web image, but the same spot can look soft in a large print or tight crop. That is why sensor format, inspection size, and sharpness target can change the answer even when lens, aperture, and focus distance stay the same.
| Decision | What changes the answer | Common mistake |
|---|---|---|
| Portrait separation | Wide aperture, close focus, longer lens, and background distance. | Assuming blur strength also guarantees both eyes are sharp. |
| Product or macro detail | Magnification, aperture, subject depth, and focus placement. | Stopping down without checking diffraction, motion, or focus stacking needs. |
| Landscape or street focus | Hyperfocal distance, near limit, aperture, and viewing target. | Seeing infinity in the far limit and forgetting the foreground near limit. |
| Video close-up | Subject sway, operator drift, sensor format, and inspection size. | Planning from a still frame while the actor or camera keeps moving. |
Several familiar choices pull the range in opposite directions. Opening the aperture gives stronger separation but leaves less room for focus error. Stopping down makes the focus band wider but may require more light, a slower shutter, higher ISO, or a decision about diffraction. Moving closer narrows the range quickly, which is why macro and close portrait work often demand stricter focus discipline than a landscape at the same f-number.
Hyperfocal distance is useful, but it is easy to overread. Focusing at or beyond the hyperfocal point can push the far limit to infinity under the chosen CoC, yet the foreground still begins at a near limit. A landscape can have infinity covered while a nearby rock or flower remains outside the acceptable range.
Depth of field is a planning estimate for geometry and viewing assumptions. It does not measure autofocus accuracy, lens field curvature, subject movement, stabilization, shutter speed, sharpening, diffraction, or how a viewer will judge the final image. The number is strongest when it is paired with test frames, magnified review, and a realistic idea of how the photograph will be shown.
Start from the camera setup you are most likely to shoot, then use the result tabs to decide whether the focus band is wide enough for the subject and final use.
The most important fields are Near focus limit, Focus distance, Far focus limit, and Total depth of field. The focus distance is the exact plane you selected. The near and far limits are the estimated boundaries where blur stays within the chosen CoC. Values outside that range do not become instantly unusable, but the blur is no longer within the selected sharpness target.
A far limit of infinity means the focus distance has reached the hyperfocal condition for the current aperture, focal length, and CoC. It does not mean the whole scene is sharp. Check the near limit before relying on a foreground rock, product edge, or person near the camera.
| Cue | Boundary used here | Practical response |
|---|---|---|
| Very thin focus tolerance | Total depth of field is under 8% of focus distance. | Stop down, back up, reduce focal length, or plan focus bracketing. |
| Moderate focus tolerance | Total depth of field is at least 8% and under 25% of focus distance. | Keep the critical detail on the focus plane and watch motion. |
| Strong background blur | Background blur ratio is at least 8x CoC. | Expect clear separation, but still judge lens character and background texture. |
| Subject exceeds frame | Subject frame coverage is above 100% vertical. | Back up, use a wider lens, or accept that the entered subject will crop. |
| Motion allowance uncovered | The narrower tolerance around focus is less than the entered motion allowance. | Increase the f-number, back up, or reduce focal length unless shallow blur matters more. |
Use Bokeh Preview and Focus Map as planning aids, not as proof of final image quality. A high blur ratio does not guarantee pleasing bokeh, and a broad focus band does not guarantee a sharp file if the lens, shutter speed, focus method, or final enlargement cannot support the shot.
Classical depth of field math models a lens as a simple optical system with a chosen acceptable blur diameter. The equations are sensitive to focus distance because small focus changes at close range move the near and far limits quickly. That is why macro and close portrait work can have a focus band measured in millimeters or centimeters, while a stopped-down landscape may stretch many meters.
Sensor format affects the default CoC and the field-of-view estimate. It does not magically change the optics of the same physical lens. The actual focal length, aperture f-number, focus distance, and CoC drive the sharpness range; sensor width and height then determine framing measurements such as angle of view, field width, and subject coverage.
The focus-limit equations use millimeters for focal length, focus distance, CoC, and derived distances. User-entered meters, centimeters, feet, and inches are converted to millimeters before the calculation.
| Symbol | Meaning | Mapped input or output |
|---|---|---|
| f | Physical lens focal length. | Focal length, in millimeters. |
| N | Aperture f-number. | Aperture. |
| c | Circle of confusion on the sensor. | Sensor format plus Sharpness target, or custom CoC. |
| s | Camera-to-subject focus distance. | Subject distance. |
| H | Hyperfocal distance. | Hyperfocal distance in Focus Brief and Marker Ledger. |
For a full-frame 85 mm lens at f/1.8 focused at 2.2 m with a large-print CoC of about 0.021 mm, the hyperfocal distance is about 191 m. The near limit is about 2.18 m, the far limit is about 2.22 m, and the total depth of field is about 4.9 cm. The front and rear tolerance are only about 2.4 cm and 2.5 cm, so a small subject sway can matter.
Sharpness profiles scale the sensor format's baseline CoC. A smaller CoC makes the standard stricter and reduces the reported depth of field.
| Sharpness target | CoC multiplier | Meaning |
|---|---|---|
| Screen preview / forgiving | 1.35 | Allows a larger blur circle for smaller or more forgiving viewing. |
| Standard print / normal viewing | 1.00 | Uses the sensor format's baseline planning value. |
| Large print | 0.70 | Requires smaller blur circles for more demanding enlargement. |
| Critical crop / fine detail | 0.50 | Uses a stricter CoC for close inspection or heavy cropping. |
| Custom circle of confusion | Entered value | Uses the positive millimeter value supplied by the user. |
Background blur is estimated for one entered background plane by comparing image distance at the focus plane with image distance at the background plane. The result is shown as a sensor blur diameter and as a multiple of the selected CoC.
| Quantity | Rule | Interpretation limit |
|---|---|---|
| Far limit | Reported as infinity when H is less than or equal to focus distance. | The near limit still decides where acceptable sharpness begins. |
| Field width | Subject distance times sensor width divided by focal length. | An estimate for planning composition, not a calibrated lens profile. |
| Field height | Subject distance times sensor height divided by focal length. | Frame orientation swaps which sensor dimension is vertical. |
| Subject coverage | Subject height divided by field height, multiplied by 100. | Values above 100% mean the entered subject height exceeds the vertical frame. |
| Full-frame equivalent | Physical focal length multiplied by the selected crop factor. | Useful for framing comparison, not for the focus-limit formula itself. |
Visible distances are rounded for readability after calculation. Metric output can switch between millimeters, centimeters, meters, and kilometers by size; imperial output switches between inches and feet. Infinite far limits remain explicit so they are not mistaken for a large finite distance.
The result is an optical planning estimate. It assumes classical depth of field equations, one selected CoC, and a geometric background blur estimate. Real images can differ for reasons the equation cannot see:
Portrait headshot. A full-frame camera with an 85 mm lens at f/1.8, focused at 2.2 m under the Large print target, reports a Total depth of field near 4.9 cm. The Focus Brief puts the near limit around 2.18 m and the far limit around 2.22 m. That is enough for a deliberately shallow portrait, but the Planning Guide should make you check subject sway and eye placement before shooting wide open.
Tabletop product. A 70 mm lens at f/5.6 focused 80 cm from a small product can still report only about 2 cm of total depth of field under the Critical crop target. If Subject frame coverage is above 100% vertical and the front edge is soft, back the camera up, use a smaller aperture, reduce subject magnification, or plan focus stacking instead of assuming f/5.6 is already deep enough.
Landscape check. A 24 mm lens at f/8 focused at 3 m on full frame can push the far limit far into the scene, but the Near focus limit may still sit around 1.6 m under a large-print target. If the foreground is closer than that, focus farther does not solve the problem. The useful follow-up is to compare the Aperture Ladder or change focus distance until the near limit covers the foreground.
Input warning. If a background is entered at 2.0 m while the subject distance is 2.2 m, the background blur estimate cannot describe a plane behind the subject. Move Background distance beyond the focus distance, then check Background blur plane and Background separation again.
The sharpness target changes the CoC. Screen preview uses a more forgiving value, while Large print and Critical crop use stricter values. A stricter CoC pulls the near and far limits closer to the focus distance.
Enter the actual focal length on the lens. The calculator uses Sensor format and crop factor separately for framing and full-frame equivalent reporting.
Infinity appears when the focus distance reaches or passes the hyperfocal condition for the current focal length, aperture, and CoC. Check Near focus limit before assuming the foreground is covered.
No. Background blur ratio measures blur diameter relative to the selected CoC at the entered background plane. Pleasing bokeh also depends on lens design, aperture shape, aberrations, background texture, and highlight placement.
Check for a positive focal length and aperture, a subject distance farther than the focal length, a background distance behind the subject, a non-negative subject height and motion allowance, and a positive custom CoC if Custom circle of confusion is selected.