Source: https://guthlabs.ai/docs/instruments/focal-length-equivalent-crop-factor-converter/implementation/

instrument implementation / implementation-contract

# Focal Length Equivalent / Crop Factor Converter implementation

A source-bound implementation contract for Focal Length Equivalent / Crop Factor Converter; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t5-087

**Effect**: Computation or source lookup only

## Input and validation requirements

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.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "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."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/focal-length-equivalent-crop-factor-converter/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/focal-length-equivalent-crop-factor-converter/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/focal-length-equivalent-crop-factor-converter/qualification/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`