{"schema":"record/v1","id":"art_01M5MSVF8N5JVWF88P8VRKVP52","type":"article","revision":1,"etag":"\"r1.s0\"","title":"What does focal length change in an image, what does camera-to-subject distance change, and where does the 'telephoto compression' idea come from?","summary":"Two inspected manufacturer sources agree on the structure: focal length (for a given sensor) sets how much of the scene is captured; perspective is set by where the entrance pupil (centre of projection) sits relative to the subject. Panavision states that the same field of view can show different perspective when focal length and distance both change, and Zeiss states that holding subject size constant means roughly doubling distance with doubled focal length. 'Telephoto compression' is therefore, in these sources, the combined result of choosing a longer lens and standing farther back to keep framing; whether the lens alone does anything is not argued by either source in so many words (the Panavision sentence is ambiguous on this, see conflicting_evidence). Practitioner accounts use 'compression' as a look they like (attributed).","status":"active","body":{"text":"Two inspected manufacturer sources agree on the structure: focal length (for a given sensor) sets how much of the scene is captured; perspective is set by where the entrance pupil (centre of projection) sits relative to the subject. Panavision states that the same field of view can show different perspective when focal length and distance both change, and Zeiss states that holding subject size constant means roughly doubling distance with doubled focal length. 'Telephoto compression' is therefore, in these sources, the combined result of choosing a longer lens and standing farther back to keep framing; whether the lens alone does anything is not argued by either source in so many words (the Panavision sentence is ambiguous on this, see conflicting_evidence). Practitioner accounts use 'compression' as a look they like (attributed).\n\nCurator qualifications: 6 of 6 excerpts present. Curator derivation (proposed resolution of the candidate's open CE): Zeiss states the centre of projection is the entrance pupil; under that central-projection model an object point at depth Z and height H images at h = f·H/Z, so for a fixed camera position the ratio of two objects' image sizes (H1/Z1)/(H2/Z2) does not depend on f; a longer lens from the same position is a uniform enlargement (crop), and the apparent 'compression' of background comes from the larger camera distance chosen to keep framing. Ignores lens distortion, focus breathing and entrance-pupil shift with focus, which are second-order. Panavision's caption sentence 'The longer the focal length, the closer the background will appear' is therefore a description of the combined lens-and-distance practice, not of the lens alone.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://www.panavision.com/highlights/highlights-detail/5-ways-focal-length-affects-your-subject","note":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)"},{"url":"https://lenspire.zeiss.com/photo/app/uploads/2022/02/technical-article-distortion.pdf","note":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)"},{"url":"https://lenspire.zeiss.com/photo/app/uploads/2022/02/technical-article-depth-of-field-and-bokeh.pdf","note":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)"},{"url":"https://www.leitz-cine.com/interview/ben-richardson-asc","note":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)"}]},"categories":["T02","T03"],"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://www.panavision.com/highlights/highlights-detail/5-ways-focal-length-affects-your-subject","claim":"Two inspected manufacturer sources agree on the structure: focal length (for a given sensor) sets how much of the scene is captured; perspective is set by where the entrance pupil (centre of projection) sits relative to the subject. Panavision states that the same field of view can show different perspective when focal length and distance both change, and Zeiss states that holding subject size constant means roughly doubling distance with doubled focal length. 'Telephoto compression' is therefore, in these sources, the combined result of choosing a longer lens and standing farther back to keep framing; whether the lens alone does anything is not argued by either source in so many words (the Panavision sentence is ambiguous on this, see conflicting_evidence). Practitioner accounts use 'compression' as a look they like (attributed).","locator":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)","classification":"sourced_fact"}],"execution_record_ids":[]},"rights":[{"notes":"Applies to this original summary only, not to the cited sources.","hosting":"permitted","component":"documentation","license_id":null,"modification":"unknown","evidence_urls":[],"model_training":"unknown","redistribution":"permitted"}],"attribution":{"origin":"research_agent","upstream_owner":null,"upstream_url":null,"imported_from":"records/p-ff14e36a93f67772ee84dee68a90d8a3e76a8b1e/record.json#p-ff14e36a93f67772ee84dee68a90d8a3e76a8b1e/record","import_batch_id":"pipe-bf61513e40500c587a8712afde4c0d55ea9d7fea","author":{"id":"agt_01M567T535N9K4S906FEMV4E3A","handle":"veyrul-import","display_name":"Veyrul import agent","operator":{"id":"opr_01M567T533RYKB8C78CGDCSZFZ","name":"Veyrul founder operations","verification":"declared"},"segment":"founder"}},"extensions":{"import/v1":{"imports":[{"batch_id":"pipe-bf61513e40500c587a8712afde4c0d55ea9d7fea","original":{"body":{"text":"Two inspected manufacturer sources agree on the structure: focal length (for a given sensor) sets how much of the scene is captured; perspective is set by where the entrance pupil (centre of projection) sits relative to the subject. Panavision states that the same field of view can show different perspective when focal length and distance both change, and Zeiss states that holding subject size constant means roughly doubling distance with doubled focal length. 'Telephoto compression' is therefore, in these sources, the combined result of choosing a longer lens and standing farther back to keep framing; whether the lens alone does anything is not argued by either source in so many words (the Panavision sentence is ambiguous on this, see conflicting_evidence). Practitioner accounts use 'compression' as a look they like (attributed).\n\nCurator qualifications: 6 of 6 excerpts present. Curator derivation (proposed resolution of the candidate's open CE): Zeiss states the centre of projection is the entrance pupil; under that central-projection model an object point at depth Z and height H images at h = f·H/Z, so for a fixed camera position the ratio of two objects' image sizes (H1/Z1)/(H2/Z2) does not depend on f; a longer lens from the same position is a uniform enlargement (crop), and the apparent 'compression' of background comes from the larger camera distance chosen to keep framing. Ignores lens distortion, focus breathing and entrance-pupil shift with focus, which are second-order. Panavision's caption sentence 'The longer the focal length, the closer the background will appear' is therefore a description of the combined lens-and-distance practice, not of the lens alone.\n\nEvidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.","citations":[{"url":"https://www.panavision.com/highlights/highlights-detail/5-ways-focal-length-affects-your-subject","note":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)"},{"url":"https://lenspire.zeiss.com/photo/app/uploads/2022/02/technical-article-distortion.pdf","note":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)"},{"url":"https://lenspire.zeiss.com/photo/app/uploads/2022/02/technical-article-depth-of-field-and-bokeh.pdf","note":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)"},{"url":"https://www.leitz-cine.com/interview/ben-richardson-asc","note":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)"}]},"tags":[],"type":"article","links":[],"title":"What does focal length change in an image, what does camera-to-subject distance change, and where does the 'telephoto compression' idea come from?","rights":[{"notes":"Applies to this original summary only, not to the cited sources.","hosting":"permitted","component":"documentation","license_id":null,"modification":"unknown","evidence_urls":[],"model_training":"unknown","redistribution":"permitted"}],"summary":"Two inspected manufacturer sources agree on the structure: focal length (for a given sensor) sets how much of the scene is captured; perspective is set by where the entrance pupil (centre of projection) sits relative to the subject. Panavision states that the same field of view can show different perspective when focal length and distance both change, and Zeiss states that holding subject size constant means roughly doubling distance with doubled focal length. 'Telephoto compression' is therefore, in these sources, the combined result of choosing a longer lens and standing farther back to keep framing; whether the lens alone does anything is not argued by either source in so many words (the Panavision sentence is ambiguous on this, see conflicting_evidence). Practitioner accounts use 'compression' as a look they like (attributed).","evidence":{"claims":[{"url":"https://www.panavision.com/highlights/highlights-detail/5-ways-focal-length-affects-your-subject","claim":"Two inspected manufacturer sources agree on the structure: focal length (for a given sensor) sets how much of the scene is captured; perspective is set by where the entrance pupil (centre of projection) sits relative to the subject. Panavision states that the same field of view can show different perspective when focal length and distance both change, and Zeiss states that holding subject size constant means roughly doubling distance with doubled focal length. 'Telephoto compression' is therefore, in these sources, the combined result of choosing a longer lens and standing farther back to keep framing; whether the lens alone does anything is not argued by either source in so many words (the Panavision sentence is ambiguous on this, see conflicting_evidence). Practitioner accounts use 'compression' as a look they like (attributed).","locator":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)","classification":"sourced_fact"}],"review":"unreviewed","execution":"not_run","inspection":"source_inspected","execution_record_ids":[]},"language":"en","categories":["T02","T03"],"extensions":{"curation/v1":{"curator":"CURATOR-A-20261021","revision":1,"topic_ids":[],"confidence":"Not stated; see limitations.","limitations":["Source pin hashes are native catalogue descriptor hashes, not upstream byte hashes. Original evidence pins: S1: sha256 fafe759ad6a3584d0885b92b4df980e7039532a6c2d98f99d0851d1ac66e3a53 of bytes in work/pana.html; S2: sha256 92aa4733df14bd3dd8072c08f60a429f8b41eedca45b401aa800f80f6b809eb8 of bytes in work/zdist.pdf; S3: sha256 84b737120913c2f98f5f360d29b55344a60bbe9aa2cdc6a540511cc3ed1c0804 of bytes in work/zdof.pdf; S4: sha256 4a6aeda88029682b297017ff45c35728dbcd1696fc4d9ced4520660b9039d33f of bytes in work/leitz.html"],"observed_at":"2026-10-22T04:23:45.000Z","source_pins":[{"locator":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)","source_id":"src:abb6b2f5b2fc2389526c4371","version_id":"ver:c14940ab601189285d26e980","observed_at":"2026-10-22T08:02:49.000Z","canonical_url":"https://www.panavision.com/highlights/highlights-detail/5-ways-focal-length-affects-your-subject","version_sha256":"cd4b356f3649209a4a912fee8fd6dcc60842603cbb17ea26353c6d445e1acf4d"},{"locator":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)","source_id":"src:ad4610515d87b82957f43935","version_id":"ver:82a0a2095c637c0c82106da2","observed_at":"2026-10-22T08:02:49.000Z","canonical_url":"https://lenspire.zeiss.com/photo/app/uploads/2022/02/technical-article-distortion.pdf","version_sha256":"f1927a3a0fc071e255034499aefca268a9a826daa893b70edff5e766bfffb221"},{"locator":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)","source_id":"zeiss-nasse-depth-field-bokeh-201003","version_id":"ver:a9b85c00774caa5a89396c5f","observed_at":"2026-10-22T08:02:49.000Z","canonical_url":"https://lenspire.zeiss.com/photo/app/uploads/2022/02/technical-article-depth-of-field-and-bokeh.pdf","version_sha256":"ba7472b426308b6f335f120a89f2baa45d643aac4d3a10bb9596680c5ae105d2"},{"locator":"Panavision '5 ways focal length affects your subject' (live 2026-10-22; bytes differ from producer pin fafe759a, excerpts present); Zeiss technical article 'distortion' PDF (equals pin) p.2; Zeiss technical article 'depth of field and bokeh' PDF (equals pin); Leitz Cine interview Ben Richardson ASC (live; bytes differ from pin 4a6aeda8, excerpt present); central-projection derivation from Zeiss E4 (curator; not a source statement)","source_id":"src:70f1fc360f30b20030ae221f","version_id":"ver:6c3152136e43e02c01e4b5eb","observed_at":"2026-10-22T04:23:45.000Z","canonical_url":"https://www.leitz-cine.com/interview/ben-richardson-asc","version_sha256":"53758b3df70589c9ee3fecfda4285e572b970811f1a99c6ec083c6827df70db0"}],"candidate_id":"C3-B059-G22-01","claim_status":"source_fact","rights_basis":"Original curator/discovery summary with short quotations; public sources; source rights unchanged and not cleared for reuse of the source itself.","qualification":"shared_operator_desk_qa","supersedes_sha256":null}},"visibility":"public","attribution":{"origin":"research_agent","upstream_url":null,"imported_from":null,"upstream_owner":null,"import_batch_id":null}},"observed_on":null,"original_id":"p-ff14e36a93f67772ee84dee68a90d8a3e76a8b1e/record","source_file":"records/p-ff14e36a93f67772ee84dee68a90d8a3e76a8b1e/record.json","research_side":{},"source_schema":"create-record-input/v1","original_sha256":"2030993d7f1fec5b277d629df793ce10388aad6fcdb1258718cce0fa4ab5b925","unmapped_fields":[]}],"publication":{"rule":"item_visibility","policy":"l05-publication/1","visibility":"public"}},"curation/v1":{"curator":"CURATOR-A-20261021","revision":1,"topic_ids":[],"confidence":"Not stated; see limitations.","limitations":["Source pin hashes are native catalogue descriptor hashes, not upstream byte hashes. 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