{"schema":"record/v1","id":"art_01M5MCTR9QVY0DFCV4M5HX516J","type":"article","revision":1,"etag":"\"r1.s0\"","title":"When lens metadata reports \"focal length\", which focal length is it, and what reference point do entrance-pupil and focus values use?","summary":"Cooke distinguishes nominal, pinhole and effective focal length and warns that mixing them causes matchmove problems; positions are referenced to a nominal image plane 52 mm behind the PL flange; pinhole focal length is available as /i lens metadata on supporting lenses and otherwise must be measured by grid calibration or solved in a match-move. Record which focal length a metadata field carries.","status":"active","body":{"text":"Cooke distinguishes nominal, pinhole and effective focal length and warns that mixing them causes matchmove problems; positions are referenced to a nominal image plane 52 mm behind the PL flange; pinhole focal length is available as /i lens metadata on supporting lenses and otherwise must be measured by grid calibration or solved in a match-move. Record which focal length a metadata field carries.\n\nCurator qualifications: Vendor paper read 2026-10-22; nothing calibrated. Vendor document carries a no-distribution notice: short quotes only, no reproduction (rights hold). Whether each tracking format field holds nominal or pinhole focal length not verified (camdkit reader not re-read). 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[component_reuse_restriction] Eligible with rights hold; T19.03/T02.02 focal length definitions.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://cookeoptics.com/wp-content/uploads/2023/07/Cooke-Camera-Lens-Definitions-for-VFX-210723.pdf","note":"Cooke Camera and lens definitions for VFX (21/07/23) sections 2.0-4.0"},{"url":"https://github.com/SMPTE/ris-osvp-metadata-camdkit/blob/0362321d03721a07029329cfc6f9e1e47bfa2bdf/src/main/python/camdkit/arri/reader.py","note":"Cooke Camera and lens definitions for VFX (21/07/23) sections 2.0-4.0"}]},"categories":["T11","T19"],"tags":[],"language":"en","visibility":"public","moderation":{"state":"visible","reason":null},"evidence":{"inspection":"source_inspected","execution":"not_run","review":"unreviewed","review_revision":null,"claims":[{"url":"https://cookeoptics.com/wp-content/uploads/2023/07/Cooke-Camera-Lens-Definitions-for-VFX-210723.pdf","claim":"Cooke distinguishes nominal, pinhole and effective focal length and warns that mixing them causes matchmove problems; positions are referenced to a nominal image plane 52 mm behind the PL flange; pinhole focal length is available as /i lens metadata on supporting lenses and otherwise must be measured by grid calibration or solved in a match-move. 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Record which focal length a metadata field carries.\n\nCurator qualifications: Vendor paper read 2026-10-22; nothing calibrated. Vendor document carries a no-distribution notice: short quotes only, no reproduction (rights hold). Whether each tracking format field holds nominal or pinhole focal length not verified (camdkit reader not re-read). Rights/verification notes are shown as limitations (L00 0019/ADR-0011): they restrict reuse of the cited material or record what was not verified; they are not cleared by this summary.\n\nLimitations: Vendor paper read 2026-10-22; nothing calibrated. 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