| Phenomenon | ISO row |
f/ row |
Q | Baseline Sun high · clear sky |
Corrected Sun at 4° · extinction |
Notes |
|---|
■ Baseline = reference value from Espenak's table (clear sky, Sun high, airmass ≈ 1). ■ Corrected = the same scene with the Sun low, multiplied by the extinction factor. The large value is the recommended time (1/3-stop scale); below it, in brackets, the exact computed time.
Traffic light (feasibility with the chosen body and focal length, without a tracking mount): green = fine/usable · yellow = watch out for motion blur · red = impossible with these settings.
☀ Partial phase = the only row shot with an ND5 filter on the lens (MANDATORY, for your eyes and the sensor). All totality rows are shot with the filter REMOVED. The corona is tabulated continuously from 0.1 to 8 R☉ for bracketing. Per-row override: change ISO/f only on that row; ↺ restores the global value.
⚠ Note — What is verified and what is an estimate:
Solid data, NASA source: the formula t = f²/(ISO·2^Q) and the Q values for the ND5 partial phase (8), Baily's beads (12), chromosphere (11), prominences (9) and corona from 0.1 to 8 R☉ (Q from 7 to −3) come from Espenak's Table 23 (NASA/TP-2004-212762).
Estimated (not in the NASA table): the diamond ring and earthshine have no official Q. I used Q≈11 for the diamond ring (like the chromosphere: it also shows the corona ring; the bead itself is as bright as Baily's beads, Q 12) and Q≈−6 for earthshine (plausible range Q −5…−8). Treat them as a starting point and bracket widely.
Extinction is uncertain: the correction depends on the coefficient k, which at a sea horizon cannot be known in advance and can vary a lot (haze, humidity, aerosols). The linear k·X law also underestimates at 4°, so the corrected values are a reasonable minimum: be ready to add another 1–2 stops in the field by reading the histogram.
Focal length vs exposure: exposure times depend on the focal ratio (f/) and ISO, not on the focal length. Changing the millimetres does not change the times: it changes the framing (Sun Ø on the sensor) and the motion-blur threshold. The f²/(ISO·2^Q) formula uses the f-number — correct.
Practical limit (motion blur): without a tracking mount the Sun drifts ~14.6″/s (Ø ~0.53°). The 1-px trailing threshold depends on the chosen camera body (pixel size) and the focal length and is shown above ("blur beyond …").
Filter: an ND5 filter (1/100,000) is MANDATORY throughout the partial phase — for your eyes and for the sensor. Remove it only during totality and put it back as soon as the exit diamond ring ends. Never point at the partial Sun without a filter. Use manual focus.
Sources: NASA GSFC – Table 23, Solar Eclipse Exposure Guide (Espenak) · Espenak, “How to Photograph a Solar Eclipse” (mreclipse.com) · Kasten & Young (1989), Applied Optics 28, 4735 – airmass · IGN – Total eclipse of Aug 12, 2026