F-stop printing is a darkroom technique that paces test-strip exposures in equal stops (logarithmic) instead of equal seconds (linear).
Each step on an f-stop strip is a perceptually equal jump in print density — and when you read the strip carefully, a single sheet tells you both your print exposure and the paper grade your negative wants.
What is f-stop printing?
F-stop printing replaces the classic time-linear test strip with one whose exposures are spaced in stops — typically 1/3-stop steps. Because film and paper response are logarithmic, equal stops (not equal seconds) produce equal perceptual jumps in tone. The technique was systematized for darkroom workers by Gene Nocon in the 1980s and is treated in detail in Lambrecht & Woodhouse's Way Beyond Monochrome — the canonical modern reference.[1]
The payoff over a time-linear strip is twofold: every step on an f-stop strip carries equal information, and the relationship between exposure steps and paper-grade equivalents is regular enough to read both decisions from one sheet.
Why time-linear test strips fail
The classic test strip — 5, 10, 15, 20, 25 seconds — wastes most of its range. The 5-second jump from 5 to 10 doubles exposure (a full stop). The same 5-second jump from 20 to 25 is only about a third of a stop. Three of those five steps are perceptually almost identical; the first one is huge.
Print density responds to log exposure, not linear time.[2] If you want each step on a strip to give you the same useful information, the steps have to be evenly spaced in stops, not in seconds. F-stop printing is what you get when you take that observation seriously.
Stops as the natural unit
Photographers already think in stops at every other point in the chain — aperture, shutter speed, ND filters, ISO, even reciprocity adjustment. F-stop printing extends that single mental ruler to the print exposure. A 1-stop change in print exposure means the same thing as a 1-stop aperture change on the camera: double or half the light.
A 1/3-stop step is the smallest change most printers can reliably perceive on the print itself. Smaller steps (1/6-stop, 1/12-stop) exist on some timers, but 1/3-stop is the practical sweet spot for a test strip — fine enough to land an exposure precisely, coarse enough to fit a full 2-stop range on one sheet of paper.
The standard 7-step 1/3-stop test strip
A common f-stop strip uses 7 sections at 1/3-stop steps, centred ±1 stop around a base time. With a 16-second base, the strip looks like this:
| Step | Stops from base | Seconds | Equivalent paper grade* |
|---|---|---|---|
| 1 | −1 | 8.0 | 1 |
| 2 | −2/3 | 10.1 | 1.5 |
| 3 | −1/3 | 12.7 | 2 |
| 4 | base | 16.0 | 2.5 |
| 5 | +1/3 | 20.2 | 3 |
| 6 | +2/3 | 25.4 | 3.5 |
| 7 | +1 | 32.0 | 4 |
*Approximate — see the next section for how to use this column.
The 2-stop range covers most of what a single negative will need. If your initial guess at the base exposure is reasonable, the right exposure will fall somewhere on the strip — and the strip's structure also tells you whether the negative wants a different paper grade.[3]
Reading the strip — exposure AND grade in one pass
The biggest practical payoff of an f-stop test strip is that you can determine both your print exposure and the paper grade your negative wants from a single sheet.
1. Find your exposure. Pick the section where the Zone VIII highlights show the detail you want — bright but not chalky, with subtle separation in the brightest important tones. The exposure that produced that section is your print exposure.
2. Find your grade. Now scan the more-exposed sections (the darker-print strips beyond your chosen one) for where the blacks look right — deep, with shadow detail, not blocked. Count the 1/3-stop steps between your "good whites" strip and your "good blacks" strip.
3. Convert steps to grade adjustment. Each 1/3-stop step ≈ 0.5 paper-grade equivalent. A 2-step gap → ~1 grade higher than the paper you tested on; a 3-step gap → ~1.5 grades higher; and so on.
Direction matters.
- If "good blacks" is more exposed than "good whites," your negative is flatter than the paper grade you tested on — go up a grade.
- If "good blacks" is less exposed than "good whites" (the blacks are already too dark at your highlight exposure), your negative is contrastier than the paper grade you tested on — drop a grade.
The workflow described here — particularly the 1/3-stop ↔ 0.5-grade equivalence — is the core teaching of a video by distphoto.com, who runs ongoing B&W darkroom workshops. Watch the full demonstration: "Get AMAZING Darkroom Prints With This EASY Trick!". The 0.5-grade-per-1/3-stop relationship is a useful approximation; exact equivalence varies with paper response curves.[4]
Caveat: paper-speed shift between grades. Changing paper grade also changes the paper's effective speed, so the corrected-grade reprint needs its own exposure adjustment (an "exposure factor"). Calibrate this once per paper using the PEM Meter Factors Worksheet; the same distphoto.com video walks through the full calibration procedure.
Combining with split-grade printing
F-stop printing and split-grade printing compose naturally. In split-grade work, you make two separate exposures — one through a low-contrast filter, one through a high-contrast filter — and the print is the sum. Each of those two exposures can be dialled in via its own f-stop test strip, with the same exposure-and-grade reading method applied independently to highlights and shadows.
The result is a workflow with the precision of split-grade contrast control and the perceptual evenness of f-stop test strips.
Equipment and worksheets
F-stop printing is most practical with a dedicated f-stop timer that computes step times automatically.
The Darkroom Automation f-Stop Timer and the RH Designs StopClock are widely used examples; on a standard digital timer, a printed lookup table for 1/3-stop steps from a few common base times works fine.
Several reference documents from Darkroom Automation pair directly with this workflow:
- f/Stop Printing PEM Pyro Manual — the operations manual for f-stop printing with their PEM (Print Exposure Meter) system.
- PEM Paper Test Worksheet — companion worksheet for paper testing under f-stop printing.
- PEM Meter Factors Worksheet — used to calibrate the exposure-factor shift between paper grades.
Tips
- Pick a base time near the middle of your typical exposure range, usually 10–20s. A base that's already close to the right exposure means the answer falls comfortably inside the strip.
- Keep a notebook of f-stop strip results per negative type (subject, paper, developer). Patterns emerge quickly — particular negatives tend to want particular grades.
- When ±1 stop isn't enough range, repeat with a wider step (1/2-stop steps cover ±1.5 stops; 2/3-stop steps cover ±2 stops) or recentre the base time.
- "Best whites" isn't always Zone VIII — it depends on the print. Interpret the highlights step by what the print needs (a high-key portrait wants different highlights than a deep-shadow architecture print).
Learn more
The exposure-and-grade reading method described above, and the paper-speed calibration that makes it work in practice, are taught in detail by distphoto.com — who openly credits Way Beyond Monochrome as his source. If you want hands-on guidance, start with the videos and workshops; if you want the deep book reference, add WBM to your shelf.
- distphoto.com — instructor site for ongoing B&W darkroom workshops where this workflow is taught in depth.
- "Get AMAZING Darkroom Prints With This EASY Trick!" (YouTube) — the demonstration this page is based on, including the full paper/filter calibration procedure for the exposure factor between grades.
- Lambrecht & Woodhouse, Way Beyond Monochrome (2nd ed., 2010) — the canonical book reference for f-stop printing; distphoto credits it openly as his source.