Focal Length Equivalent / Crop Factor Converter

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-5

Evidence ID

t5-087

Ledger rows

1

No ledger note is attached.

Review findings

The two multiplication formulas are standard under their stated assumptions. Verdict is NEEDS_REVIEW because the exact crop-factor convention and sensor-format lookup table are unspecified, and the focal-length input/output unit policy is ambiguous.

Formula and scope findings

No additional record

Unit assumptions

• focal length is a linear measurement; the output focal length must use the same unit as the input unless an explicit conversion is performed
• aperture means the dimensionless f-number, such as f/2.8, not the physical entrance-pupil diameter
• crop factor is assumed to be relative to the 35mm still-image format, conventionally 36 mm × 24 mm, usually using diagonal-based comparison
• effective aperture for DoF equivalence assumes equivalent framing and comparable viewing/output conditions; it does not change exposure or the physical aperture

Boundary hardening

BREAK_CLAIMED · SELF_FLAGGED

Extreme focal length and crop-factor inputs produce Infinity through overflow, while zero aperture produces a mathematically defined but physically invalid f/0 result. Negative focal length also exposes an unhandled sign-convention ambiguity.

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": {
    "focalLength": 50,
    "focalLengthUnit": "mm",
    "apertureFNumber": 2.8,
    "sensorFormat": "APS-C",
    "cropFactor": 1.5
  },
  "expected_outputs": {
    "equivFocalLength": 75,
    "equivFocalLengthUnit": "mm",
    "equivApertureFNumber": 4.2
  },
  "working": "equivFocal = focal × cropFactor = 50 mm × 1.5 = 75 mm. equivAperture = aperture × cropFactor = 2.8 × 1.5 = 4.2, so the DoF-equivalent aperture is f/4.2."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

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-tranche5/tranche5-results.json
• BOUNDARY_HAZARD_CATALOG.json