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:
| Film Type | Reciprocity Starts | Compensation Needed |
|---|---|---|
| Fujifilm Acros II | ~120 seconds | Minimal (excellent) |
| Ilford Delta 100 | ~1 second | Moderate |
| Kodak Portra 400 | ~1 second | Moderate |
| Fujifilm Velvia 50 | ~4 seconds | Moderate |
| Kodak Tri-X 400 | ~1 second | Significant |
Acros II is legendary for long exposures because it maintains reciprocity up to two minutes without compensation. 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 |
| ND3200+ | 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 has compensation data for 50+ films.
Example with Kodak Portra 400:
- Metered time: 30 seconds
- Compensated time: approximately 90 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 (Portra 400): ~10-12 minutes
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 Ektar 100: Among the best colour negative films for long exposure. Relatively predictable reciprocity.
Challenging for Long Exposure
Kodak Tri-X 400: Heavy reciprocity failure. A 1-minute metered exposure might need 4-5 minutes actual time. Usable, but you'll burn through time and need careful compensation.
Fujifilm Velvia 50: Moderate reciprocity failure plus potential colour shifts at long exposures. Compensation data is less well-documented than for Acros.
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
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.