Exposure & Print Planning Reference
Three planning tables, computed directly from the same functions behind our Reciprocity & Exposure Calculator, ISO↔EV Converter, and Print DPI & Size Calculator — not a separately maintained estimate.
Reciprocity correction by metered exposure
| Metered | Near-unity (minimal failure) (p=1.1) | Typical wet-plate / dry-plate (p=1.3) | Aged or high-contrast emulsion (p=1.6) |
|---|---|---|---|
| 1s | 1s +0 stops | 1s +0 stops | 1s +0 stops |
| 2s | 2.14s +0.1 stops | 2.46s +0.3 stops | 3.03s +0.6 stops |
| 4s | 4.59s +0.2 stops | 6.06s +0.6 stops | 9.19s +1.2 stops |
| 8s | 9.85s +0.3 stops | 14.93s +0.9 stops | 27.86s +1.8 stops |
| 15s | 19.67s +0.39 stops | 33.8s +1.17 stops | 76.16s +2.34 stops |
| 30s | 42.15s +0.49 stops | 83.23s +1.47 stops | 230.88s +2.94 stops |
| 60s | 90.36s +0.59 stops | 204.93s +1.77 stops | 699.91s +3.54 stops |
| 120s | 193.69s +0.69 stops | 504.59s +2.07 stops | 2121.73s +4.14 stops |
Every corrected time comes from calling correctReciprocity() — the same function the calculator above uses — for each metered time and exponent pair. See Reciprocity Failure in Practice: Worked Exposure Examples for a narrated walkthrough of several of these exact figures.
ISO/EV conversion by lighting scenario and process speed
| Lighting scenario | Daguerreotype (~ISO 1) | Wet-plate collodion, low end (~ISO 2) | Wet-plate collodion, high end (~ISO 3) | Early dry plate / orthochromatic film (~ISO 25) |
|---|---|---|---|---|
| Open shade (modern meter, ISO 100) | EV 5.36 -6.64 stops | EV 6.36 -5.64 stops | EV 6.94 -5.06 stops | EV 10 -2 stops |
| Bright daylight (modern meter, ISO 100) | EV 8.36 -6.64 stops | EV 9.36 -5.64 stops | EV 9.94 -5.06 stops | EV 13 -2 stops |
| Dim interior (modern meter, ISO 400) | EV 0.36 -8.64 stops | EV 1.36 -7.64 stops | EV 1.94 -7.06 stops | EV 5 -4 stops |
Every target EV and stop difference comes from calling convertIsoEv()for each scenario’s reference EV/ISO against each process speed’s estimated ISO. See ISO and Exposure Value Are One Relationship: A Worked Guide for the reasoning behind several of these conversions.
Print size by plate format (captured at 1200 DPI)
| Plate format | Captured pixels | Quality (close viewing) (300 DPI) | Acceptable (poster / across-the-room viewing) (150 DPI) |
|---|---|---|---|
| Sixth-plate (~2.75 x 3.25 in) | 3300 × 3900 | 11 × 13 in | 22 × 26 in |
| Quarter-plate (~3.25 x 4.25 in) | 3900 × 5100 | 13 × 17 in | 26 × 34 in |
| Half-plate (~4.75 x 6.5 in) | 5700 × 7800 | 19 × 26 in | 38 × 52 in |
| Whole-plate (~6.5 x 8.5 in) | 7800 × 10200 | 26 × 34 in | 52 × 68 in |
Captured pixel dimensions come from calling pixelsFromSize() at a 1200 DPI capture resolution for each plate format’s nominal physical size; each print-quality column then comes from calling sizeFromPixels()on those same captured pixels at the tier’s output DPI. See Sizing a Print From a Negative: A Worked Guide for the full worked reasoning, and How Antique Photographs Degrade, and Why Originals Are Fragile for why capturing this now, at a high resolution, matters more than it might seem.
How to read these tables together
These three tables aren’t chained arithmetically into one pipeline — a print-size figure doesn’t depend on a reciprocity exponent, and an ISO/EV conversion doesn’t depend on a plate format — but they do cover the three planning questions that come up together in practice. Before a sitting: convert your meter reading to the process’s true ISO (table two), then check whether the resulting exposure time is long enough to need a reciprocity correction (table one). After a sitting or when digitizing an existing plate: check what print size the negative or plate actually supports once scanned (table three).
Every number above is reproducible: the same inputs run through the same calculators linked in each section will always return exactly what’s shown here, because this page literally calls those functions to build its tables rather than maintaining its own copy of the math.
Frequently Asked Questions
Are these tables generated from the same calculators, or a separate estimate?
The same functions. Every corrected time, stop difference, target EV, and print size on this page comes directly from calling correctReciprocity(), convertIsoEv(), and pixelsFromSize()/sizeFromPixels() — the exact functions behind the Reciprocity & Exposure Calculator, the ISO↔EV Converter, and the Print DPI & Size Calculator. A test asserts every rendered value matches a fresh call to those functions, so this page can't silently drift out of sync with the calculators.
Why three separate tables instead of one combined one?
Because they answer three genuinely different questions that happen to come up in the same planning session: how much does a long exposure need to be corrected (reciprocity), how does a metered reading translate to a much slower historical process speed (ISO/EV), and how large a print can a given negative or plate actually support once scanned (print size). Chaining all three into a single table would force artificial connections between numbers that aren't actually derived from one another.
Why is the reciprocity exponent range limited to three characteristics?
The three labeled characteristics — near-unity, typical, and aged/high-contrast — span the 1.1–2.0 range our reciprocity tool's own documentation cites as typical for historical emulsions. They're deliberately labeled as broad buckets rather than tied to a specific manufacturer or era, since a real emulsion's exponent depends on its specific formulation, age, development, and temperature — treat these as planning anchors and confirm with your own bracketed test exposures.
Why 1200 DPI as the capture resolution for the print-size table?
1200 DPI is the figure our own digitization coverage recommends for small, cased historical originals, since a small plate has little pixel budget to spare and benefits disproportionately from a higher capture resolution. The table then reports what that same capture supports at two different print-quality output DPIs, which is a separate, later choice from the capture DPI itself.
Educational and historical-reference tool only. Reciprocity exponents and historical process ISO ratings are estimates that vary by material, age, and conditions — confirm with your own test exposures before anything that matters.
Use it with
- Reciprocity & Exposure Calculator — run your own metered time and exponent instead of the fixed set above.
- ISO↔EV Converter — convert your own metered reading instead of the fixed lighting scenarios above.
- Print DPI & Size Calculator — check any pixel count, DPI, or print size, not just the standard plate formats above.