Photography Calculators

Astrophotography

Lunar Eclipse Exposure Calculator

A full moon is roughly Looney 11: f/11 at 1/ISO. Totality is another world — the umbra needs roughly 11 to 19 stops more than that, depending on how dusty the atmosphere is (Danjon scale 4 to 0). This starts from f/11 at 1/ISO, scales to your aperture, then adds phase stops. Histogram a test shot; totality changes by the minute.

Inputs

Units

Start 400 for partial; 800–3200 is common in totality.

f/

Sharpest-ish on many teles is f/5.6–f/8, not wide open.

Stops of extra time versus a full moon at f/11, 1/ISO.

Results

Shutter
0.0006s

Starting shutter in seconds; bracket around it.

Shutter reciprocal
1,543.4

125 means 1/125 s. Under 1, read the seconds output instead.

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Calculation method

Start from Looney 11: f/11 at 1/ISO. Scale shutter by the square of (your f-number over 11) so a faster lens shortens the time. Then multiply by 2 to the phase-stop count: none for penumbral, 3 for a typical partial, 12 for a bright copper totality (Danjon 3–4), 16 for a dark one (Danjon 1–2). A very dark Danjon 0 eclipse can need about 19. Reciprocal is 1/time for shutter dials.

Exact formula

t = (1/ISO) × (N/11)² × 2^phaseStops. Reciprocal = 1/t. Phase stops: 0 penumbral, 3 partial, 12 bright total (Danjon 3–4), 16 dark total (Danjon 1–2); roughly 19 − 2L for Danjon L. Limits: Looney 11 is a full-moon starting point, not photometry; Danjon is visual; umbra brightness varies; Earthshine, clouds and tracking omitted.

White balance

Totality is red-brown. Daylight WB keeps that. Auto WB will try to make the umbra grey. Shoot RAW.

Highlight on the limb

During partial, the bright crescent will blow if you expose for the umbra. Expose for the bright part until totality, then jump to the total setting.

Frequently asked questions

Why Looney 11, not Sunny 16?

The Moon is dark grey rock in sunlight, about a stop darker than a Sunny 16 scene, so the usual starting point is f/11 at 1/ISO — one stop more exposure than Sunny 16. Phase stops are extra time on top of that moon, not on top of daylight. If your full-moon test shots look right at Sunny 16, halve every time this tool suggests.

Partial phase keeps changing.

Yes. The 3-stop partial is a middle-of-the-bite guess. Bracket as the umbra grows. Do not set one shutter for the whole eclipse.

Can I track?

A tracker lets you use the longer totality times without trailing. Untracked, also check the 500 rule on your focal length so the moon does not smear.

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