SPECIMEN / 001LT-001
ILFORD
HP5 Plus
ISO 400 · P = 1.31AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
LATENTIME / THE ANALOG EVIDENCE OBSERVATORYRESEARCH EDITION 02
FILM RECIPROCITY / EXPOSURE SCIENCENot all seconds
Not all seconds
are equal.
One light meter. Four films. Four different exposures. Compare the time, understand the correction, and follow every number back to its source.
LIVE
SEC
Equal metered seconds at each film’s own EI. Not a speed ranking. Optical factors from the laboratory also apply.
01 —14 FILM SPECIMENS02 —4 MANUFACTURER DOCUMENTS03 —SOURCE-LINKED RESULTS04 —YOUR LOG STAYS LOCAL
01 / LIVE EXPOSURE LABORATORY
Follow the light. Then the evidence.
Change an input. Observe every film.
Exposure chain
SEC
Meter at the intended film EI. Add only factors not already included in the meter reading. Bellows factor = (extension / focal length)².
CORRECTED EXPOSURE
Choose comparison films4 / 6
X: metered time after optical factors (log scale). Solid: manufacturer rule. Dots: published table points. Dashed: optional site estimate. No extrapolation. Select the graph to inspect a time.
ILFORD gives no numerical upper validation limit. LATENTIME displays its formula only to 1,000 metered seconds as a site limit, not a manufacturer guarantee. Longer exposures require testing.
02 / FILM EVIDENCE ARCHIVE
A specimen for every second.
14 film identities. Original documents. No anonymous coefficients.
SPECIMEN / 002LT-002
ILFORD
FP4 Plus
ISO 125 · P = 1.26AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
SPECIMEN / 003LT-003
ILFORD
Delta 100
ISO 100 · P = 1.26AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
SPECIMEN / 004LT-004
ILFORD
Delta 400
ISO 400 · P = 1.41AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
SPECIMEN / 005LT-005
ILFORD
Delta 3200
EI 3200 · P = 1.33AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
SPECIMEN / 006LT-006
ILFORD
Pan F Plus
ISO 50 · P = 1.33AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
SPECIMEN / 007LT-007
ILFORD
SFX 200
ISO 200 · P = 1.43AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
SPECIMEN / 008LT-008
ILFORD
XP2 Super
ISO 400 · P = 1.31AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
SPECIMEN / 009LT-009
ILFORD
Ortho Plus
ISO 80 · P = 1.25AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
SPECIMEN / 010LT-010
HARMAN
Kentmere 100
ISO 100 · P = 1.26AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
SPECIMEN / 011LT-011
HARMAN
Kentmere 400
ISO 400 · P = 1.30AT CURRENT FILM INPUT—
≤ 1 s: no correction · upper limit unstated
HARMAN · Dec 2023 · p.1
SPECIMEN / 012LT-012
FUJIFILM
ACROS II (120)
ISO 100 · APERTURE RULEAT CURRENT FILM INPUT—
< 120 s: unchanged · 120–1000 s: +½ aperture
NEOPAN 100 ACROS II (120) · p.1
SPECIMEN / 013LT-013
KODAK
TRI-X 400
ISO 400 · PUBLISHED TABLEAT CURRENT FILM INPUT—
Official long-exposure anchors: 1 / 10 / 100 s
F-4017 · Dec 2016 · p.2
SPECIMEN / 014LT-014
FOMA
Fomapan 100 Classic
ISO 100 · PUBLISHED TABLEAT CURRENT FILM INPUT—
Official long-exposure anchors: 1 / 10 / 100 s
FOMAPAN 100 · May 2022 · p.1
03 / FIELD INSTRUMENTS
Out of the lab. Into the night.
A deliberate exposure. A record worth keeping.
FIELD TIMER / MANUAL SHUTTER
READY00:00:20.4
ILFORD HP5 Plus · 20.4 s
Operate the shutter yourself. Keep this page visible and disable screen auto-lock. Background tabs or a locked device may delay the display and completion alert. The countdown uses an absolute clock, not interval ticks.
Darkroom field log
Stored only in this browser. Export a backup before clearing browser data. Personal records do not change manufacturer data.
Your exposure evidence
| DATE / FILM | METERED → ACTUAL | CONDITIONS / OBSERVATION | EVIDENCE |
|---|
EXPOSURE EVIDENCE COURT
A difference is a question.
Save a field record, then compare the actual exposure against the stored model reference. A difference in seconds alone does not prove correct density or establish a better correction rule.
No field evidence yet.
EVIDENCE PROTOCOL
Conditions before conclusions.
Compare EI, scene luminance, developer and dilution, agitation, temperature, time, storage and meter accuracy. A density measurement needs its method, reference exposure and instrument details in the notes. A scan impression remains an observation, not a calibrated test.
04 / SOURCE REGISTRYVERIFIED / PRIMARY SOURCES01Original document ↗ 02Original document ↗ 03Original document ↗ 04Original document ↗
Every second has a source.
Documents manually checked on 3 November 2026. Registry v1.0. No automated revision tracking.
HARMAN / Film Reciprocity Failure Compensation
Dec 2023 · p.1
11 factors; corrected seconds = metered seconds ^ P. No numerical upper bound stated. Contrast can rise; development changes depend on the scene.
KODAK / TRI-X 320 and 400 Films · F-4017
Dec 2016 · p.2
Long-exposure table: 1 → 2 s, 10 → 50 s, 100 → 1200 s. Development: −10%, −20%, −30% at those anchors. Aperture and time columns are alternatives.
FUJIFILM / NEOPAN 100 ACROS II (120)
Reciprocity Characteristics · p.1
Below 120 s: no correction. From 120 to 1000 s: open the lens by ½ stop. The site does not turn this aperture instruction into an asserted shutter time.
FOMA / FOMAPAN 100 Classic
May 2022 · p.1
Published factors at 1, 10 and 100 s: ×2, ×8 and ×16. No manufacturer interpolation rule is supplied. Site interpolation is opt-in and labeled.
Source Revision Detective · version history
v1.0 · 2026-11-03: initial manually verified registry. The dates above identify the documents actually checked; they are not claims that these are the newest editions. No earlier source snapshots have been collected, so no document changes are asserted. Future revisions must be compared with retained originals before being listed.
Light does not always add up.
What is reciprocity failure?
At low light levels, equal total light delivered over a longer time can produce less density on film. Stable development centres form less efficiently. A meter reading therefore becomes a starting point, and the film-specific correction supplies the next step.
Optics first. Film second.
The site multiplies metered seconds by 2^ND, the squared aperture ratio and the bellows factor. It then applies the selected reciprocity model. Applying an ND factor after the film correction produces a different answer and is not this model. Use the same EI on your meter and in your field notes.
Numbers are starting points.
Manufacturer references do not promise a finished photograph. Light measurement, contrast and processing affect results. Bracket important exposures and record the whole process. The ±½-stop plan varies exposure duration around the corrected starting time; it is an experiment, not a separate validated reciprocity model.
Why do some films show no number?
A table point is not a continuous formula. Between the published anchors, enable explicitly labeled site estimates or consult the original graph. Outside supported intervals the site leaves a gap.
Can I rank different ISO films?
Equal metered seconds compare reciprocity behaviour, not total capture speed. For the same scene and aperture, meter each film at its intended EI first. Delta 3200 is a product name and exposure-index class; use the EI you actually meter at.
Does the site change development time?
No automatic development calculation is performed. TRI-X notes preserve the anchor-point reductions from Kodak; ILFORD suggests scene-dependent testing if contrast rises. Do not stack alternative aperture and shutter corrections.
Are field logs shared?
No. Log entries remain in browser local storage and are not submitted to this site. JSON backups can be imported here. Existing Blogger and Google advertising services may still process data under their own policies.
How are estimates calculated?
For neighboring anchors (x₀,y₀) and (x₁,y₁), w = ln(t/x₀)/ln(x₁/x₀), then y = exp(ln(y₀) + w·ln(y₁/y₀)). This is a site assumption, not a manufacturer recommendation or a digitized official curve.
About LATENTIME
An independent reference tool for film photographers. Not affiliated with film manufacturers. Data and editorial methodology: LATENTIME. Symbol illustration created for this project. Sources checked manually; community observations never overwrite primary references.
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