What makes good subject isolation?

Strong isolation requires shallow DOF (wide aperture, longer focal length, close distance) AND sufficient subject-to-background distance. A 85mm f/1.4 with 5m between subject and background gives excellent isolation. The background should be far enough to fall well outside the DOF zone.

How is the isolation score calculated?

The Isolation Index is an indicative in-house guide, not a physical unit. It is derived directly from the background blur-disc diameter (the size each out-of-focus background point grows to on the sensor), scaled by 200 and capped at 100. The physically meaningful number is the Background Blur Disc itself: a larger disc means stronger background separation. As a rough guide, a blur disc above about 0.25 mm gives clearly visible separation and above 0.40 mm melts the background away.

Which has more impact: aperture or distance?

Subject-to-background distance often has more practical impact than aperture. An f/4 lens with 10m between subject and background can isolate better than f/1.4 with 1m separation. However, wider apertures always help — the ideal is both wide aperture and good separation.

Does focal length affect isolation?

Yes, in two ways. Longer focal lengths give shallower DOF at the same aperture and framing. They also compress perspective, making backgrounds appear larger but more blurred. For portrait isolation, 85-135mm on full frame is the classic choice.

Subject Isolation Calculator — Background Separation

Measure how well your subject separates from the background with a combined DOF and blur analysis.

Focal Length

Actual lens focal length in mm (longer focal lengths shorten DOF and increase background blur)

Aperture

f-number you are shooting at — wider apertures (lower f, e.g. f/1.8) blur the background more

Subject Distance

Distance from camera to the subject you are focusing on

Background Distance

Distance from camera to the background behind the subject

SensorChoose your sensor format (sets the circle of confusion) or pick Custom to enter your own CoC in mm

How We Calculate This

Subject DOF

Depth of field is found from the hyperfocal distance H = f²/(N·c) + f (f = focal length, N = f-number, c = circle of confusion for your sensor), then the near and far limits near = H·s/(H + (s − f)) and far = H·s/(H − (s − f)), with far = ∞ once the subject reaches H. DOF is far − near.

Background Blur Disc

Each out-of-focus background point grows into a disc on the sensor of diameter d = (f² / (N·(s − f))) × |b − s| / b, where s is the subject distance and b is the background distance. Equivalently d = (f · (f/N) · |b − s|) / (b · (s − f)). A bigger disc means a more dissolved background.

Isolation Index

An indicative 0–100 guide (not a physical unit) derived from the blur-disc diameter in mm, scaled by a multiplier and capped. Use the Background Blur Disc in mm as the absolute, physically meaningful figure.

Frequently Asked Questions

Related Calculators

DOF Calculator

Calculate near focus limit, far focus limit and total depth of field for any lens, aperture and subject distance combination. Free online calculator.

Hyperfocal Distance Calculator

Find the hyperfocal distance for maximum depth of field in landscape photography. Enter focal length, aperture and sensor size. Free online calculator.

Circle of Confusion Calculator

Calculate the circle of confusion for your sensor size, viewing distance and print dimensions. Essential for accurate DOF calculations. Free calculator.

Bokeh Calculator

Estimate background blur disc size for any lens, aperture and subject-to-background distance. Predict bokeh quality before you shoot. Free online calculator.

Focus Stacking Calculator

Plan focus stacking sequences for macro and landscape photography. Calculate the number of frames and focus step distance needed. Free online calculator.

Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.