Lenses and Focus
Focus Breathing Calculator
Measure effective framing change between focus distances.
Enter the optical values
For Focus Breathing, keep sensor format, units, focus state, and reference planes attached to the entries.
The lens or focus result will appear here with supporting checks.
Separate physical and equivalent values for Focus Breathing
Measure effective framing change between focus distances.
Focus Breathing Calculator reports framing change from Frame width at near focus, Frame width at far focus. Quantify focus-induced angle-of-view change.
Equivalence describes a matched comparison and does not alter the lens engraved specification.
Inputs that define framing change
Record Frame width at near focus and Frame width at far focus from one camera, lens, focus setting, and frame. Preserve the unit printed beside Frame width at near focus and Frame width at far focus; converting one without the other changes the geometry behind framing change.
Identify whether Frame width at near focus came from EXIF, the lens scale, a test frame, a sensor specification, or direct measurement before comparing another Focus Breathing setup.
The calculation behind Focus Breathing
Measure effective framing change between focus distances.
For Focus Breathing, the page keeps the intermediate geometry visible and rounds only the displayed framing change. Compare the calculated ratio with a direct dimensional ratio.
Worked check with the published values
For Focus Breathing, calculate the defaults and save the displayed framing change with its supporting quantities. Change only Frame width at near focus in the Focus Breathing example, predict the direction of framing change, and calculate again.
Restore Frame width at near focus and confirm the first result returns. That reset test distinguishes a real change in framing change from a stale Frame width at near focus value or an unnoticed unit conversion.
Where the framing change model stops
Measured scene widths must use the same camera position, sensor crop, and reference plane.
Framing change cannot judge the lens rendering, autofocus repeatability, decentering, field curvature, contrast, stabilization, or the success of the intended composition.
Measurement boundary for Focus Breathing
Define the reference plane for Frame width at near focus and what is included in Frame width at far focus. For Focus Breathing, a distance referenced to the sensor cannot silently replace one measured from the lens front, mount, principal plane, or subject surface.
For Focus Breathing, list any crop, correction profile, teleconverter, extension, close-up element, breathing, or shift already represented by Frame width at far focus. Apply each Focus Breathing adjustment once—either inside the entered measurement or explicitly afterward, never in both places.
Reading the result in practice
Compare framing change with a test frame, focus chart, measured field width, sensor specification, or known limiting case. If that check disagrees with framing change, inspect the units and the reference plane used for Frame width at near focus before changing the formula.
The Lens Magnification Calculator addresses a nearby lens question, but its output should be transferred only when the format and geometry remain the same.
A second comparison for Focus Breathing
Use Nyquist Lens Resolution Calculator for the next defined quantity. Even if it also reports millimeters, meters, degrees, or pixels, its assumptions are not interchangeable with Focus Breathing.
Label the alternative setup and change one variable so the difference in framing change remains explainable.
Precision and available settings
Keep full precision while framing change feeds another calculation, then round to the precision supported by the lens scale, rail, sensor specification, or field measurement.
Extra decimals in framing change cannot repair uncertainty in Frame width at near focus, Frame width at far focus, pupil location, focus breathing, or the selected sharpness criterion.
Saving a reproducible lens record
Save Frame width at near focus, Frame width at far focus, framing change, camera format, lens state, focus distance, and date. Mark nominal specifications separately from measured values.
For Focus Breathing, when the lens, format, crop, focus, or camera position changes, preserve the earlier Focus Breathing case and calculate a labeled replacement.
Designing a useful test for Focus Breathing
For Focus Breathing, choose a subject with measurable edges or planes and keep the camera position fixed unless distance is the quantity under test. Record Frame width at near focus before the first frame and confirm Frame width at far focus from the same lens state. For Focus Breathing, note the marked focal length and focus state beside Frame width at near focus; internal focusing or zoom position can change the effective geometry.
After the published Focus Breathing baseline, create a second case that changes only Frame width at far focus by a measurable amount. A doubled distance, one-stop aperture change, known crop, measured rail movement, or fixed pixel dimension gives framing change an independent directional expectation.
For Focus Breathing, inspect both center and edge when using framing change; projection, coverage, vignetting, distortion, diffraction, or field curvature may vary across the image. A center-frame Focus Breathing measurement may agree while the edge departs because of behavior outside this simplified equation.
Using framing change in a shooting decision
For Focus Breathing, translate the number into one concrete choice: move the camera, change focal length, select an aperture, set a rail position, confirm image-circle coverage, or decide whether the subject will occupy enough pixels. Keep that action beside the saved framing change so another person knows why the calculation was made.
If framing change falls between marked Focus Breathing controls, retain the unrounded value and document the setting actually used. Test the neighboring available Frame width at far focus value instead of claiming more adjustment precision than the lens, rail, focus scale, tilt mechanism, or camera position provides.
For Focus Breathing, after the photograph, compare the recorded frame with the expected framing change. Save deviations that repeat across tests; they can reveal focus breathing, a nominal sensor dimension, an entrance-pupil offset, a lens-specific projection, or another stable correction worth applying in future Focus Breathing work.
Questions about focus breathing calculator
What does Focus Breathing Calculator calculate?
It calculates framing change from Frame width at near focus, Frame width at far focus. Measure effective framing change between focus distances.
Which measurement should I verify first?
Confirm Frame width at near focus, its unit, and its reference plane before using the other entries.
What is the main limitation?
Measured scene widths must use the same camera position, sensor crop, and reference plane.
How can I check framing change?
Run the defaults, change only Frame width at far focus, predict the direction, and restore the starting value.