Lumiverse · DOF Simulation · Practical optics guide · Updated October 13, 2026

Depth of field explained: aperture, focus and blur.

Depth of field is not a fixed property of a lens. It changes with focal length, aperture, focus distance, sensor format, and the amount of enlargement a final image receives. This guide explains what the simulator shows, what its numbers mean, and where a real photograph can differ.

What depth of field means

Only one distance is exactly in focus on the sensor. Objects in front of and behind that distance form small circles instead of points. Those circles look acceptably sharp when they stay below a chosen circle of confusion (CoC). The near and far limits shown by the simulator are therefore a practical sharpness convention, not a hard optical boundary.

A smaller aperture (a larger f-number such as f/8) narrows the cone of light and reduces those circles. Focusing farther away also increases the sharp range. A wider aperture such as f/1.8 produces a shallower range at the same distance, which can separate a subject from the background.

How to use the simulator

1. Start with the camera and lens

Choose a Portrait, Group photo or Landscape example for a quick start, or select your camera and a compatible lens. On a phone, open the Gear tab. The camera sensor dimensions affect field of view and the default CoC. Zoom lenses use an intermediate focal length so you can explore a useful range instead of only the endpoints. A prime lens has one fixed focal length; select a zoom or Custom lens to change it. Catalog selections link to manufacturer sources with verification dates.

2. Set the subject and background distances

Focus distance is the camera-to-subject distance. Background distance is the camera-to-background distance. Keeping a background far behind the subject usually increases visible separation, but the amount of blur also depends on focal length and framing. Use the depth overlay to see how each illustrated plane is treated.

On a phone, use the Settings tab. Drag a slider for exploration or type an exact value beside it. Distance fields use metres or feet according to the Distance units switch; focal length always uses millimetres. For example, type 3.5 into Focus distance in metric mode for a subject 3.5 metres away, not 3500. An empty or out-of-range entry displays an explanation and keeps the last valid shot. Press Escape to restore that value.

3. Compare aperture choices

Move the aperture slider from a small f-number to a larger one. The preview and the calculated near/far limits update together. The comparison feature can pin one setup so you can compare two apertures, lenses, or focus distances without relying on memory.

Select Pin as setup A before changing a setting. A stays fixed while the controls edit B. Desktop shows both previews; a phone shows A · Pinned and B · Current tabs to keep each image readable. Selecting A does not change which shot the controls edit. The comparison below the controls reports the difference in total depth of field. Share copies a link containing both shots, so a visitor can reproduce your comparison without an account.

Framing a complete person on a small screen

All three current person assets include legs and footwear. If a face or torso fills the preview, the camera is simply too close for a full-body composition at that focal length. Choose Fit full person to move the simulated camera back. This changes the actual focus distance and therefore the calculated depth of field; it is not a cosmetic image shrink. The background distance also moves to preserve the previous subject-to-background gap where the supported range allows.

The eye line stays around the upper third as magnification changes. Advanced controls let you change the assumed standing height and turn on Keep subject size when comparing lenses or sensor formats. These are flat, generated people for framing exercises, not three-dimensional scans: their face anchors and height calibration are approximate, and they cannot demonstrate whether a nose and both eyes are simultaneously sharp.

The phone preview keeps the selected sensor's aspect ratio; a vertical screen does not silently rotate your camera or change its field of view. It stays above the controls while you scroll. Use Hide preview for more room to type, then Show preview to return. The Scene tab changes the person, background and preview mode. For optical experiments use Depth model; Photo backdrop cannot recover sharpness missing from its source image.

What the calculations include

The numerical model uses paraxial thin-lens geometry. It derives hyperfocal distance, magnification, field of view, near and far DOF limits, and the blur diameter for the selected background. The default CoC is based on the sensor diagonal divided by 1500, a transparent educational convention that can be changed in Advanced controls.

Depth model scenery is split into discrete object planes. Each plane receives its own calculated defocus circle, while point lights use an aperture-shaped footprint for an illustrative bokeh result. The Airy-disk value is an estimate at 550 nm; it helps show why very small apertures can trade depth of field for diffraction softness.

These calculations are intentionally inspectable rather than pretending to reproduce a particular camera's JPEG engine. The preview is a teaching aid, not a measurement instrument.

Why a real photograph may look different

• Lens focus breathing can change framing as focus distance changes.
• Pupil magnification, aberrations, mechanical vignetting, and optical design change blur character.
• The photo backdrop has softness already present in the source image; stopping down cannot restore detail that was never captured.
• Viewing distance, display size, output resolution, and sharpening change whether a blur circle appears acceptably sharp.
• The simulator does not reconstruct a continuous depth map from a photograph or model every individual lens.

Quick experiments

• Portraits: keep both eyes sharp — a worked 85 mm comparison with settings you can load.
• Groups: plan for two rows of faces — check the nearest and farthest eyes at three apertures, then prepare a real test.
• Landscapes and hyperfocal distance — when infinity is acceptable, and when to focus more cautiously.
• Compare sensor formats fairly — separate framing, depth of field, and exposure.
• Background blur versus depth of field — move the background without changing the sharp range around your subject.
• Circle of confusion explained — compare two sharpness criteria on the same photograph.
• Equations and validation — inspect the exact model and its limitations.
• Reproducible reference data — compare eleven fixed setups and download their inputs and results.
• Test your own camera — print or copy a field note comparing predicted limits with your real photographs.

For a portrait, choose an 85 mm lens, focus on the subject, and move the background farther away. Then compare f/1.8 with f/5.6. For a landscape, try a wide lens and focus farther away, then inspect the hyperfocal result. Finally, use the same framing with different sensor formats: the field of view and the acceptable CoC change, so “the same f-number” does not guarantee the same visual result.

Frequently asked questions

Does a full-frame camera always have less depth of field?

No. Depth of field comparisons depend on the framing, focal length, aperture, focus distance, and output criterion. A larger sensor often uses a longer focal length to keep the same framing, which can change the result. Compare matched setups rather than sensor labels alone.

Is the far limit always finite?

No. At or beyond the hyperfocal distance, the calculated far limit can extend to infinity. The result panel marks that open-ended range instead of inventing a finite distance.

Why does the photo mode not become sharper at f/16?

Photo mode uses a finished image without a depth map. It can illustrate composition and overall softness, but it cannot recover detail hidden by the original image or apply a physically separate blur to every object. Use Depth model when you want to study per-plane blur.

Educational note: Use the simulator to form a shooting plan, then confirm the result through your camera's viewfinder or a test frame. The displayed values are calculated estimates, not a guarantee of focus for every viewing condition.

Verify the numbers: reproducible reference examples · equations and limitations · publisher and corrections.