ND Filter Stop / Exposure Time Calculator

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Audio, Music, Photography & Color

Tranche

tranche-4

Evidence ID

t4-193

Ledger rows

1

No ledger note is attached.

Review findings

The mathematical formulas are standard and correct under the stated unit and factor assumptions. NEEDS_REVIEW because the specification does not define whether ND labels such as ND1000 are treated as exact exposure factors or rounded stop equivalents, does not define validation and rounding behavior, and has an empty honest_label. The honest label should state that ND naming conventions are approximate and that the result is an exposure-time calculation, not a guarantee of camera-specific shutter-speed availability.

Formula and scope findings

No additional record

Unit assumptions

• baseTime is a positive shutter duration measured in seconds; the output newTime uses the same time unit.
• stops is an exposure-stop count, where each stop doubles the required exposure time.
• filterFactor is the multiplicative exposure-time factor, not optical density or light transmission; stops = log2(filterFactor) is valid only for filterFactor > 0.
• The factor convention must be explicit: an exact factor of 1000 equals log2(1000) = 9.965784... stops, while the common photographic label ND1000 is conventionally rounded to 10 stops.
• Human-readable time requires a defined rounding and formatting policy.

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

The specification admits filter_factor = 0, for which log2(0) and the derived stop count are undefined; the calculator must reject it. ND1000 also produces materially different results depending on whether it is interpreted as exact factor 1000 or the common rounded value of 10 stops.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "inputs": {
    "baseTimeSeconds": 0.008,
    "stops": 3
  },
  "expected_outputs": {
    "newTimeSeconds": 0.064,
    "humanReadable": "64 ms (approximately 1/15.6 s)"
  },
  "working": "2^3 = 8. 0.008 s × 8 = 0.064 s. 0.064 s × 1000 = 64 ms. Reciprocal shutter speed: 1 ÷ 0.064 = 15.625, so approximately 1/15.6 s."
}

Related workflows

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json · VERIFIED_CLEAN
• evidence-tranche4/tranche4-results.json
• BOUNDARY_HAZARD_CATALOG.json