Long exposures on film offer something digital can't easily replicate: the organic accumulation of light over minutes or even hours, with the unique tonal characteristics of film emulsions. But film adds a complication digital photographers don't face: reciprocity failure.
This guide covers everything you need for successful long exposures on film, from understanding reciprocity to choosing the right gear and calculating multi-minute exposures.
This guide assumes you've completed:
What is Reciprocity Failure?
The "reciprocity law" states that exposure is linear: halving the light and doubling the time should give the same result. This holds true for normal exposures, but breaks down at extremes.
At very long exposures (typically beyond 1-10 seconds depending on film), the film becomes less efficient at recording light. A metered 30-second exposure might actually need 60 seconds or more to achieve correct density.
Film sensitivity decreases when photons arrive too slowly. The silver halide crystals need a certain rate of light hits to form a stable latent image. Below that threshold, some energy is "lost" and doesn't contribute to the exposure.
When Does It Apply?
Different films have different reciprocity characteristics. This is what each maker publishes:
| Film | No correction needed up to | What the maker publishes beyond that |
|---|---|---|
| Fujifilm Acros II | 120 seconds | +½ stop from 120 to 1,000 seconds |
| Ilford Delta 100 | 1 second | P = 1.26: a metered 10 seconds becomes about 18, and 100 becomes about 331 |
| Kodak Portra 400 | 1 second | Nothing: Kodak says to make tests for longer exposures |
| Fujifilm Velvia 50 | 1 second | +⅓ stop at 4 seconds, up to +1 stop at 32 seconds; 64 seconds is not recommended |
| Kodak Tri-X 400 | 1/10 second | +1 stop at 1 second, +2 stops at 10 seconds, +3 stops at 100 seconds |
Acros II is legendary for long exposures because it needs no compensation under two minutes, and only half a stop up to about 17 minutes. For night photography, this makes it exceptional.
Essential Equipment
Typical costs: Quality tripod: £50-150. Cable release: £10-30. ND filters: £20-100 depending on quality and density.
Tripod
A sturdy tripod is non-negotiable. For multi-minute exposures, even subtle movement creates blur.
What to look for:
- Weight rating well above your camera weight
- No centre column extension (or keep it retracted)
- Hook for hanging weight in wind
- Legs that spread wide for low angles
Avoid: Lightweight travel tripods for serious long exposure work. They flex and vibrate.
Cable Release
Never touch the camera during exposure. A cable release (mechanical or electronic depending on your camera) lets you trigger and hold the shutter without introducing vibration.
For exposures over 30 seconds, you'll typically use Bulb mode, holding the shutter open with the cable release. Locking cable releases let you lock it open without holding it.
ND Filters
Neutral density filters extend exposure times in daylight, enabling long exposures when light levels would otherwise require fast shutter speeds.
| Filter | Stops | Effect |
|---|---|---|
| ND8 | 3 stops | Modest extension |
| ND64 | 6 stops | Good for overcast days |
| ND1000 | 10 stops | Strong, enables multi-second in daylight |
| ND32000 | 15 stops | Extreme, multi-minute in daylight |
Quality matters: Cheap ND filters introduce colour casts (often magenta or green). For colour film, invest in quality glass or resin filters. B&W shooters can be more forgiving.
Light Meter or Phone App
Your camera's meter may not read accurately in very low light. A handheld meter with low-light capability or a phone app can help establish a baseline reading that you then compensate for reciprocity.
Calculating Extended Exposures
Step 1: Get a Base Reading
Meter the scene to get a "normal" exposure time. If light levels are too low for your meter, try:
- Metering at a higher ISO and calculating back (meter at ISO 3200, shoot at ISO 100 = 5 stops more time)
- Using spot meter on the brightest area and placing it appropriately
- Using Sunny 16 backwards from known conditions
Step 2: Apply Reciprocity Compensation
Use the reciprocity data for your specific film. Our reciprocity calculator gives the makers' published compensation for about three dozen films, and says plainly when a maker publishes none.
Example with Ilford Delta 100 (Ilford's P = 1.26):
- Metered time: 30 seconds
- Compensated time: about 73 seconds (30 to the power 1.26)
Example with Kodak Tri-X 400 (Kodak's table):
- Metered time: 10 seconds
- Compensated time: 50 seconds (Kodak's figure for a metered 10 seconds)
Example with Fujifilm Acros II:
- Metered time: 30 seconds
- Compensated time: 30 seconds (no compensation needed under 120s)
Step 3: Account for ND Filters
If using ND filters, calculate the base exposure first, then add filter factor, then apply reciprocity compensation to the final time.
Example:
- Base exposure: 1/4 second at f/11
- With ND1000 (10 stops): 256 seconds (~4 minutes)
- With reciprocity compensation (Delta 100, P = 1.26): about 18 minutes, or 1,080 seconds (bracket around this time)
This is why Acros II is popular for long exposures: you can skip step 3 entirely for most practical exposures.
Tripod Technique
Getting sharp long exposures requires more than just owning a tripod.
Setup
- Extend thickest leg sections first, thinnest last
- Keep centre column down unless absolutely necessary
- Spread legs wide for stability
- On soft ground, push legs in firmly
- Hang weight from centre hook in wind (your camera bag works)
During Exposure
- Shield the eyepiece (light leaks through viewfinder on SLRs)
- Stand back from the tripod during exposure
- Block wind with your body if needed
- Don't touch anything until exposure completes
Mirror Lock-Up
If your camera offers mirror lock-up (MLU), use it. The mirror slap at the start of exposure can cause vibration, especially on medium format cameras. Trigger MLU, wait 2-3 seconds for vibration to settle, then trigger the shutter.
Film Choices for Long Exposure
Best for Long Exposure
Fujifilm Neopan Acros II: The king of long exposure. Reciprocity failure doesn't begin until around 120 seconds, and compensation is minimal even at very long times. Fine grain, excellent tonality. The obvious choice if shooting B&W.
Ilford Delta 100: Good reciprocity characteristics with well-documented compensation. Fine grain suitable for enlargement.
Kodak T-Max 400: Modest published compensation: +⅓ stop at 10 seconds and +1½ stops at 100 seconds (300 seconds), with no development change.
Challenging for Long Exposure
Kodak Tri-X 400: Heavy reciprocity failure. A 1-minute metered exposure needs roughly 10 minutes, reading between the 50 seconds Kodak gives for a metered 10 and the 1,200 seconds it gives for a metered 100. Kodak also advises cutting development by 10% at 1 second, 20% at 10 seconds and 30% at 100 seconds. Usable, but you'll burn through time and need careful compensation.
Fujifilm Velvia 50: Moderate reciprocity failure plus potential colour shifts at long exposures. Fujifilm publishes compensation from 4 seconds (+⅓ stop), with magenta filtration from 5M at 4 seconds to 12.5M at 32 seconds, and says 64 seconds is not recommended.
Colour Shifts
Some films develop colour casts at long exposures. Colour negative film is more forgiving (correctable in scanning/printing), but slide film bakes in any shifts permanently.
If colour accuracy matters for very long exposures, test your specific film and exposure time before committing to important shots.
Common Long Exposure Subjects
Moving Water
Silky waterfalls and smooth seas require exposures of several seconds to several minutes. Start around 1-4 seconds for slight smoothing, 30+ seconds for complete smoothing.
Light Trails
Vehicle lights create trails at exposures of 10-30 seconds typically. Longer isn't always better here—you want defined trails, not a solid blur.
Star Trails
True star trails require exposures of 20+ minutes for visible trails, or multiple shorter exposures stacked later. This is where Acros II's reciprocity characteristics really shine.
Architecture
Long exposures can remove pedestrians and cars from urban scenes. Anything moving during a multi-minute exposure effectively disappears. This typically requires ND filters during daylight.
Troubleshooting
Overexposed Results
- Reciprocity compensation was too aggressive
- ND filter not as strong as rated
- Light leak during long exposure
Underexposed Results
- Reciprocity compensation not enough
- Metering error at low light levels
- Bellows factor (if using close focus) not accounted for
Soft Images
- Camera movement during exposure
- Tripod instability (wind, soft ground)
- Mirror slap vibration
- Focusing error (harder to confirm in low light)
Colour Shifts
- Normal for some films at long exposures
- Can indicate light leaks (often reddish)
- Cheap ND filters can introduce casts
Film Choice for Long Exposures
Reciprocity failure varies enormously between film stocks. Choosing the right film for long exposure work can mean the difference between straightforward shooting and laborious calculations with uncertain results.
Films That Handle Long Exposures Well
Fujifilm Neopan Acros 100 II: The standout choice. Fujifilm says no compensation is needed under 120 seconds, and only +½ stop from 120 to 1,000 seconds. For any long exposure work in black and white, Acros II simplifies everything.
Ilford Delta 100: Well-documented reciprocity data published by Ilford, using their formula-based compensation system (the "p factor" method). This makes calculation straightforward and reliable. Fine grain suits enlargement from long-exposure negatives.
Ilford FP4 Plus: Another Ilford film with published reciprocity data. Ilford gives it the same reciprocity factor as Delta 100 (P = 1.26), and the film is widely available.
Kodak T-Max 400: Kodak's published compensation is small: +⅓ stop at 10 seconds and +1½ stops at 100 seconds.
Films That Struggle with Long Exposures
Kodak T-Max 100: Often assumed to struggle, but Kodak's data shows modest compensation: +⅓ stop at 1 second, +½ stop at 10 seconds and +1 stop at 100 seconds, with no development change.
Kodak Tri-X 400: Heavy reciprocity failure: Kodak's table runs from +1 stop at 1 second to +3 stops at 100 seconds, so you will spend considerably more time waiting for exposures to complete. Kodak publishes nothing beyond 100 seconds.
Most slide films (E-6): Slide film is problematic for two reasons: reciprocity failure itself, and colour shifts that develop at long exposure times. Unlike colour negative, where shifts can be corrected in scanning, slide film records these shifts permanently in the transparency. Fujifilm Velvia 50 needs compensation from about 4 seconds; Provia 100F is the exception: Fujifilm lists no correction up to 128 seconds.
Ilford's Published Reciprocity Data
Ilford publishes a reciprocity factor for each of its main black and white films. HP5 Plus (1.31), FP4 Plus (1.26), Delta 100 (1.26), Delta 400 (1.41) and Delta 3200 (1.33) all use the same formula: corrected time equals metered time to the power of the factor. If you are shooting long exposures regularly, this documented reliability is a strong reason to choose Ilford stocks. Use our reciprocity calculator to look up compensation values for specific films and exposure times.
Colour Negative for Long Exposures
Kodak publishes no reciprocity figures beyond one second for its Portra films (160, 400 and 800) or for Ektar 100; its data sheets say to make tests for longer exposures. Colour negative's generous exposure latitude helps here, because it can absorb some error in your compensation, but you are working from your own tests rather than the maker's numbers. Bracket generously and keep notes.
Very Long Exposures
For exposures of ten minutes or longer — star trails, extreme ND filter work, pinhole photography — consider shooting large format if you have access to it. A single sheet of 4x5 or 8x10 film can be sacrificed for a test exposure, letting you dial in compensation before committing to the final shot. This is impractical with roll film, where a test frame means advancing past it and losing the option to reshoot in the same position.
At these extreme durations, film choice becomes critical. Even Acros II needs compensation beyond two minutes, and most other films require times that multiply rapidly. Plan for long waits and bring a book.
Summary
- Reciprocity failure requires exposure compensation beyond 1-10 seconds (film dependent)
- Fujifilm Acros II has exceptional reciprocity characteristics
- A solid tripod and cable release are essential
- ND filters enable long exposures in daylight
- Calculate: base exposure → ND filter factor → reciprocity compensation
- Use mirror lock-up and shade the viewfinder eyepiece
- Test your specific film at your target exposure times for critical work
Long exposure photography on film rewards patience and planning. The results—organic, continuous accumulation of light on a physical medium—have a quality that's difficult to replicate digitally.
Sources
- Kodak Professional Tri-X 320 and 400 technical data (F-4017), Kodak Alaris
- Kodak Professional T-Max 100 technical data (F-4016), Kodak Alaris
- Kodak Professional Portra 400 technical data (E-4050), Kodak Alaris
- Kodak Professional T-Max 400 technical data (F-4043), Kodak Alaris
- Ilford film reciprocity failure compensation (Dec 2023), Ilford/Harman
- Ilford FP4 Plus technical information, Ilford/Harman
- Velvia 50 data sheet, section 6, Fujifilm (copy distributed by Maco)
- Neopan 100 Acros II data sheet, Fujifilm