Long exposure photography with film has a character all of its own, but there is one complication that every film photographer eventually encounters: reciprocity failure.
Once exposure times become sufficiently long, the exposure indicated by your light meter may no longer give the result you expect. Film does not maintain a perfectly linear response indefinitely, which means longer exposures can require additional exposure time.
If you shoot Fomapan black and white film, I’ve created a simple way of working this out in the field.
Fomapan Reciprocity is my free reciprocity calculator for iPhone and iPad. Select your Fomapan film and metered exposure and the app calculates the corrected exposure time for you.
No printed charts. No calculations beside the camera. Just the corrected exposure when you need it.
Download Fomapan Reciprocity free from the App Store
What Is Film Reciprocity Failure?
Under normal photographic conditions, shutter speed and aperture have a reciprocal relationship.
If you reduce the amount of light reaching the film by one stop, you can compensate by doubling the exposure time.
For example, changing an exposure from 1 second to 2 seconds represents an additional stop of exposure.
At sufficiently long exposure times, however, photographic film stops behaving in this perfectly predictable way. The film requires more exposure than a straightforward calculation would suggest.
This effect is known as reciprocity failure.
It is particularly important when photographing:
- Landscapes in low light
- Night scenes
- Interiors
- Architecture
- Long exposure seascapes
- Scenes using ND filters
- Black and white photography using coloured filters
- Pinhole photography
Pinhole photographers in particular can encounter reciprocity failure frequently because the very small effective apertures of pinhole cameras often produce exposure times measured in seconds or minutes.
Fomapan Film and Reciprocity Failure
Fomapan remains a popular range of traditional black and white films.
The current FOMA black and white film range includes Fomapan 100 Classic, Fomapan 200 Creative and Fomapan 400 Action, alongside several other specialist films.
When exposure times become long, photographers need to account for the reciprocity characteristics of the film they are using.
You can, of course, carry reciprocity tables or look up the appropriate correction.
But that’s not particularly convenient when you’re standing beside a camera in the dark.
That’s why I created the app.
Introducing Fomapan Reciprocity
Fomapan Reciprocity is a simple field calculator specifically designed for correcting long exposures when using supported Fomapan black and white films.
Choose the film stock, select the exposure indicated by your meter and the app calculates the corrected exposure.
The current version also provides full, half and third stop exposure intervals, optional ND and coloured filter compensation, an exposure countdown timer and warnings when a calculation goes beyond published reciprocity data.
The idea behind it is deliberately simple.
Spend less time calculating exposure and more time making photographs.
Fomapan Reciprocity App Features
The current version of Fomapan Reciprocity includes:
- Reciprocity correction for supported Fomapan films
- Full stop exposure intervals
- Half stop exposure intervals
- Third stop exposure intervals
- Optional ND filter compensation
- Optional coloured filter compensation
- Built in exposure countdown timer
- Warning when calculations exceed published reciprocity data
- Light and dark mode
- No account required
- No advertising
- No data collection
Apple’s App Store privacy information confirms that the developer declares no data is collected by the app.
And the app is completely free.
Full, Half and Third Stop Exposure Intervals
One of the improvements introduced in version 1.1 is the ability to work in full, half or third stop exposure intervals.
This makes the app easier to use with different cameras and metering methods.
If your camera or meter works in third stop increments, for example, you don’t need to convert those readings into full stops before calculating the corrected exposure.
Select the interval that matches the way you’re working and use the corresponding metered exposure.
ND and Coloured Filter Compensation
Long exposure photographers frequently use filters, and black and white film photographers may also use coloured filters to alter tonal relationships within the photograph.
Both affect exposure.
Version 1.1 of Fomapan Reciprocity therefore includes optional compensation for ND and coloured filters.
Rather than calculating the filter factor separately and then working out reciprocity correction, the app can incorporate filter compensation into the exposure calculation.
This is particularly useful when combining a naturally long exposure with additional filtration.
Built In Exposure Countdown Timer
Once the corrected exposure becomes long enough, another problem appears.
You have to time it.
Fomapan Reciprocity includes a built in exposure countdown timer, so once you’ve calculated the corrected exposure you can use the app to time it as well.
That makes the app useful for the complete long exposure process rather than simply providing a number that you then have to transfer to another timer.
What Happens Beyond the Published Reciprocity Data?
There is an important distinction between a calculated value supported by published film data and an extrapolated value.
Fomapan Reciprocity therefore provides a warning when calculations exceed the published data used by the app.
I think this is important.
A calculator should not present an extrapolated value as though it has exactly the same certainty as a value calculated within the available published data.
The warning lets you know when you’ve moved beyond that range so you can make your own judgement about the exposure.
A Useful Tool for Pinhole Photography
Pinhole photography and reciprocity failure tend to go hand in hand.
Because a pinhole camera uses an extremely small aperture, exposures can quickly extend into seconds or minutes, even when the available light doesn’t seem particularly low.
You might meter a scene and calculate the conventional exposure correctly, only to find that reciprocity failure means the film actually requires considerably more exposure.
That’s where having the calculator on your phone becomes particularly convenient.
If you’re interested in pinhole photography, you can also use the pinhole exposure resources here on Digital Black & White alongside the Fomapan Reciprocity app.
Internal link: Pinhole Camera Exposure Charts
How to Use the Fomapan Reciprocity Calculator
The basic workflow is straightforward:
- Meter the scene.
- Determine the normal exposure before reciprocity correction.
- Open Fomapan Reciprocity.
- Select the Fomapan film you’re using.
- Choose your exposure interval.
- Select the metered exposure.
- Add ND or coloured filter compensation if required.
- Read the corrected exposure.
- Use the built in countdown timer for longer exposures.
It keeps the technical side of the process out of the way so you can concentrate on the photograph.
Why I Made Fomapan Reciprocity
Digital Black & White has always been about practical photography.
Some of the tools I develop solve fairly involved problems, such as scanning and converting black and white film negatives.
Others solve one very specific photographic problem.
Fomapan Reciprocity falls firmly into the latter category.
Reciprocity calculations aren’t the interesting part of making a photograph. The photograph is.
If an app can take care of the calculation quickly and reliably enough that you can get back to using the camera, then it has done what it was designed to do.
Free, Private and No Account Required
I also wanted Fomapan Reciprocity to remain simple.
There is no account to create and no advertising. According to the privacy information supplied for the App Store listing, the app collects no user data.
Install it, use it when you need it, and get on with your photography.
That’s it.
Download Fomapan Reciprocity Free
Fomapan Reciprocity is available free from the Apple App Store for iPhone and iPad.
The current version is 1.1 and requires iOS 18.0 or later on iPhone or iPadOS 18.0 or later on iPad.
Download Fomapan Reciprocity free from the App Store
If you shoot Fomapan film, particularly for long exposure, landscape, night or pinhole photography, it’s a handy little tool to keep on your phone.
Continue Your Black and White Film Workflow
Once you’ve exposed and developed your negatives, Digital Black & White also has extensive resources covering the next part of the process: getting those negatives into the digital darkroom.
You may also find these useful:
Film Negative Scanning: A Practical Guide to Better Results at Home
How To Convert B&W Film Negatives: The Linear Scan Workflow
SilverFast SE for 16 Bit Linear RAW Film Scans
From calculating the exposure through to scanning and converting the finished negative, the aim is the same: make the technical side of black and white photography easier so you can concentrate on the image.