Calculators·Exposure & Light Values

Calculate the optimal aperture.

Find the optimal aperture for macro photography while balancing diffraction blur and depth of field – for maximum image quality up close.

Includes the distinction between nominal and effective aperture, plus hints on when focus stacking is the smarter choice.

◆Macro-optimised
◆Diffraction limit
◆Pupil ratio
◆Focus stacking hints

Optimal Aperture Calculator

Calculate the optimal aperture for macro and close-up photography. The optimal aperture considers both depth of field and diffraction blur.

Reproduction ratio

1:1 = 1.0, 1:2 = 0.5, 2:1 = 2.0, etc.

Circle of confusion (CoC)

Automatic by format

CoC: 0.028844 mm

Enter manually

Wavelength of light (mm)

Default: 0.00055 mm (550 nm – green light)

The optimal aperture is the theoretically best aperture for macro shots. It takes both the desired depth of field and the unavoidable diffraction blur at small apertures into account.

Nominal aperture: The aperture set on the lens, based on infinity focus.

Effective aperture: The actual aperture taking the reproduction ratio (bellows factor) into account.

Optimal aperture (nominal):

f = CoC / (1.22 × λ × (M + 1))

Effective aperture:

f_eff = f_nominal × (M + 1)

Here CoC is the circle of confusion, λ is the wavelength of light (550 nm) and M is the reproduction ratio.

The CoC defines from which size a point is perceived as out of focus. It depends on the sensor size and the intended output size.

Automatic calculation: CoC = sensor diagonal / 1500 (for digital sensors)

35mm film: Traditionally 1/30 mm = 0.033 mm

◆Basics

What the optimal aperture does.

A theoretical concept with major practical value: the aperture at which depth of field and diffraction are in balance – the one that delivers the sharpest image at the sensor.

Definition & purpose

Finding the balance.

The optimal aperture is a theoretical concept that determines the best aperture for macro shots. It considers the balance between the desired depth of field and unavoidable diffraction blur. With macro shots this balance is especially important, because small apertures provide more depth of field but can reduce sharpness through diffraction.

Nominal vs. effective

Two aperture terms.

Nominal aperture: the aperture set on the lens, based on focus at infinity.

Effective aperture: the actual aperture taking the bellows factor at close focus into account. It is always larger (darker) than the nominal aperture.

◆Calculation basics

The formulas behind the optimal aperture.

Two formulas combined deliver the optimal aperture for any macro situation – the second adjusts it for a real setup with extension.

f = CoC ÷ (1.22 × λ × (M + 1))

Optimal aperture (nominal).

f_eff = f_nominal × (M + 1)

Effective aperture with bellows factor.

CoC: circle of confusion diameter · λ: wavelength of light (550 nm) · M: magnification

◆Use cases

Three magnification tiers in the macro range.

The higher the magnification, the more critical diffraction becomes – and the more focus stacking pays off as an alternative to a very small aperture.

Close-ups (1:4 to 1:1)

Sweet spot of the optimal aperture.

Ideal range. Good balance between depth of field and diffraction. Apertures between f/8 and f/16 are often optimal.

Real macros (1:1 to 3:1)

Diffraction becomes critical.

Optimal aperture is often f/5.6 to f/11. Focus stacking becomes the preferred technique for maximum sharpness across a larger area.

Extreme macros (>3:1)

Diffraction dominates.

Wide apertures (f/2.8 – f/5.6) with focus stacking are usually the only solution for sharp images at these magnifications.

◆Circle of confusion

What the CoC means.

The circle of confusion diameter determines from what size a point is perceived as out of focus. It's the secret main ingredient of every depth-of-field calculation.

Dependencies

Three influencing factors.

Sensor size (larger sensor = larger CoC)
Output size (larger prints = smaller CoC required)
Viewing distance (closer viewing = smaller CoC required)

Rules of thumb

Quick values for everyday use.

Digital: sensor diagonal ÷ 1500

35 mm film: 1/30 mm (0.033 mm)

◆Diffraction

Why small apertures make images soft.

Diffraction is physics – not a lens problem. It occurs with every lens and forces macro photographers to find a compromise.

What is diffraction?

Light bends at the blades.

Diffraction is a physical phenomenon: light waves are "bent" at the aperture blades. The smaller the aperture, the stronger the diffraction – and the softer the image. Diffraction blur is independent of lens quality and occurs with all lenses.

The trade-off

Depth of field vs. diffraction.

In macro photography you weigh up: more depth of field through smaller apertures vs. less diffraction blur through wider apertures. The optimal aperture shows you the theoretically best compromise between the two factors.

◆Alternative

Focus stacking instead of very small aperture.

When the optimal aperture isn't enough, you combine multiple shots into one image – the result exceeds anything that's possible with a single exposure.

Approach

Use a wide aperture (f/5.6 – f/8), take multiple shots with different focus points and combine the images in post.

Benefits

Maximum sharpness without diffraction, full control over depth of field and the best image quality even at extreme magnifications.

◆FAQ