Macro Exposure Compensation Calculator

Frequently Asked Questions

Why do I lose light in macro photography?

At high magnification the lens is extended far from the sensor, so the effective aperture becomes f × (1 + magnification). At 1:1 that is two extra stops of light loss versus the marked f-number.

How many stops do I lose?

Exposure correction in stops ≈ log₂((1 + M)²). At 1:1 (M = 1) that is 2 stops; at 2:1, about 3.2 stops. The calculator outputs the effective f-number and the compensation.

Does TTL metering handle this automatically?

Through-the-lens metering and TTL flash compensate automatically. The correction matters most with handheld meters, manual flash, or focus-stacking with fixed settings.

How do I recover the lost light?

Open the aperture, raise ISO, add light (macro flash), or slow the shutter on a tripod. Note that smaller effective apertures also increase diffraction softening.

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Estimates for informational purposes only.

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This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How This Calculator Works

At high magnification the lens is racked far from the sensor, spreading the same light over a larger image and dimming the exposure - the bellows or extension factor. The effective aperture is Nₕₙₙ = N × (1 + M), where M is magnification (1:1 = 1.0). The light lost in stops is log₂((1 + M)²). You can enter M directly or derive it from extension ÷ focal length, then read the corrected aperture, lost stops, and adjusted shutter.

Worked Example

At life−size (M = 1.0) the effective−aperture factor is 1 + 1 = 2, so a lens set to f/8 behaves like f/16 and loses log₂(2²) = 2 stops of light. A 1/125 s exposure must lengthen to 1/125 ÷ 4 = 1/31 s, or you open two stops, or raise ISO from 100 to 400 to compensate. At 2:1 (M = 2) the loss jumps to log₂(3²) ≈ 3.2 stops.

Real-World Use

This matters most with extension tubes, bellows, reversed lenses, and true macro lenses without internal compensation. TTL metering through the lens already accounts for the loss, but it is essential when using a handheld meter, manual studio flash, or guide−number flash, where you must add the stops yourself. It also explains why macro shooters need so much light or such slow shutter speeds and why focus stacking is common.

Common Mistakes

Double−compensating with TTL. Through−the−lens metering and TTL flash already see the dimming - do not add it again.

Using marked f−number for diffraction. Diffraction softening tracks the effective aperture, so f/8 at 1:1 diffracts like f/16.

Ignoring it with manual flash. Guide−number and studio strobe setups must add the full stop loss.

Limitations & Related Tools

The simple 1 + M model assumes a symmetric lens; highly asymmetric retrofocus or telephoto designs have a pupil−magnification correction that changes the exact factor. Internal−focus macro lenses partly hide the loss by shortening focal length. Treat the result as a reliable starting point, then confirm with the histogram or a meter. Pair this with a depth−of−field or flash guide−number calculator for close−up work; the figures are a dependable guide, not an exact optical measurement.

Macro Exposure Compensation Calculator

Frequently Asked Questions

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