ND Filter Stop / Exposure Time Calculator mechanism

Model scope

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.

No additional formula finding is recorded.

Units and conventions

• 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.

Inspectable vector

One of 4 source-bound review vectors:

{
  "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."
}

Failure boundary

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.

Other records

Sources and evidence

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

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