Hobbies & Makers · Mobile
BoxSpeed: a film photography exposure calculator for 35mm and 120
Exposure, push and pull, and reciprocity for people who shoot rolls, not files.
BoxSpeed is a film photography exposure calculator for people shooting 35mm and medium format on cameras with an unreliable meter or none at all. The app would handle exposure value, push and pull stops, equivalent aperture and shutter pairs, and reciprocity on long exposures.
Waitlist Not built yet Updated 5 September 2026
What problem does BoxSpeed solve?
Analog cameras do not agree with one another. A rangefinder with a tired selenium cell, a Hasselblad with no meter fitted, and an SLR that reads a stop and a half slow all take the same roll and want different settings. Phone apps were written around digital sensors, where speed is a dial and the histogram tells you within a second whether you were right. Film says nothing until the tank. That is where the two expensive moments happen. The first is at dusk, when the meter calls for eight seconds, you give it eight seconds, and the negative comes back thin, because film stops responding in a straight line once an exposure runs long. The second is at the lab counter, where you have to say whether the roll was shot at box speed or rated faster, and you cannot recall which body it came out of or whether the yellow filter was on for the first half.
Exposure and push/pull calculator
Aperture, shutter, and ISO in; EV, push or pull stops, equivalent exposures, and a reciprocity-corrected time out.
Free to use. No account. Nothing you type here is stored.
What would BoxSpeed do?
BoxSpeed would be a phone companion for a bag of manual cameras. You would tell it the stock, its box speed, and the speed you are actually rating this roll at, and it would return an exposure value, the push or pull in stops, and a row of equivalent aperture and shutter pairs so you can trade depth of field for a hand-holdable speed on the spot. Filter factors would come from a list you can edit, since a yellow filter and a deep orange one cost different amounts of light. Long exposures would get a reciprocity correction using the stock's own exponent, labeled as an approximation, because published figures are guidance rather than physics. A roll log would tie each roll to the body it went into, so the lab conversation and the development notes are one screen away.
How would it work?
- 1Pick the stock, its box speed, and the speed you are rating this roll at.
- 2Read the exposure value, the push or pull in stops, and equivalent aperture and shutter pairs.
- 3Add a filter factor or a metered long exposure to get a reciprocity-corrected time.
- 4Log the roll against its camera body, with the frame notes and your development recipe.
Who is it for?
- Rangefinder and TLR owners whose meter is dead, drifting, or was never fitted.
- People rating fast black and white stock two stops up in bars and gig rooms.
- Medium-format landscape shooters working after sunset, where metered times run into whole seconds.
How do you meter and bracket with sunny 16 and a notebook instead of an app?
Sunny 16 is one sentence long. In open sunlight, set the aperture to f/16 and the shutter to the reciprocal of the film speed. A roll rated at ISO 400 wants about 1/500 at f/16, or the nearest marked speed your dial actually has. From there you open up one stop at a time as the light drops: f/11 in hazy sun with soft-edged shadows, f/8 under a bright overcast where the shadow is barely there, f/5.6 when the sky is gray and heavy, f/4 in open shade or the last of a sunset. Bright sand and fresh snow go the other way, to f/22. Once you hold one pair, you can trade freely. A stop of aperture equals a stop of shutter, so f/16 at 1/500 and f/8 at 1/2000 put the same light on the film. Learning the aperture row and the shutter row in order is the whole skill, and it takes an afternoon. Bracket with the shutter rather than the aperture, so your depth of field stays where you put it. Color negative and black and white stocks hold overexposure far better than underexposure, so when you are unsure, bracket a stop over rather than a stop under. Slide film behaves the opposite way and wants precision. The notebook is what makes the roll worth anything later. Rule six columns on a page: frame, subject, aperture, shutter, filter, and what you judged the light to be. Write the roll number and the camera body on the top line, and fill the row in before you wind on. When the scans arrive, sit with the frames and the notebook together. Two rolls of that will teach you more about a meter-less body than any app, and those notes are exactly what the lab needs when you have rated a roll faster than the box.
What do people use today?
| Option | Good at | The gap |
|---|---|---|
| The sunny 16 rule and a notebook | Free, always with you, and it trains you to read light rather than a screen. | No help with reciprocity, filter factors, or push development, and the notebook does no arithmetic at dusk. |
| A handheld light meter | Incident and spot readings no phone can match, usable in cold weather with gloves on. | Gives a reading, not a decision, so push stops, filter factors, and long-exposure correction stay with you. |
| Phone light meter apps | Cheap reflected readings from the camera already in your pocket, with a usable pair of settings. | Built around digital speed, so box speed versus rated speed, reciprocity, and per-roll notes are absent. |
| Printed data sheets and reciprocity charts | The manufacturer's own figures for their own emulsion, which is the most trustworthy source available. | One sheet per stock, filed at home, and nothing connects a chart to the roll currently in the camera. |
What would it cost?
BoxSpeed
$12 once
- Exposure value, push and pull, and equivalent pairs
- Reciprocity with editable exponents per stock
- Roll and development log kept on the device
BoxSpeed Sync
$19 once
- Everything in BoxSpeed
- Roll log shared across your phone and tablet
- Backup and export of every roll you shoot
Prices are proposed. Founding members lock in the lowest price if we build BoxSpeed.
Questions people ask
What is a film photography exposure calculator?
A film photography exposure calculator converts aperture, shutter, and film speed into an exposure value, then lists the other pairs that put the same light on the negative. A film-specific one also covers push and pull stops, filter factors, and the reciprocity correction that long exposures need.
Does BoxSpeed replace a light meter?
No. BoxSpeed would do the arithmetic once you have a reading, whether that reading came from a handheld meter, a phone, or the sunny 16 rule. Owning a meter and using this for the decisions around it is a sensible pairing.
How accurate are the reciprocity numbers?
Reciprocity presets are approximations, and the app would say so on the screen. The correction uses an exponent you can edit per stock, and the manufacturer's data sheet always wins. Long exposures also drift with temperature, which no formula on a phone can know about.
Which formats would it cover?
35mm and 120 come first, because that is where most rolls are shot and where a roll log earns its keep. Large format needs sheet-by-sheet notes and film holder tracking, which is a different feature and would follow only if enough people ask.
Does it work out development times?
Development times would be stored rather than invented. BoxSpeed would keep your own recipe per stock and developer, with dilution, temperature, and agitation, then adjust the time when you push or pull. Published starting times belong to the developer's data sheet.
Would it work with no signal?
Yes. Every calculation is arithmetic done on the device, and the roll log lives locally. A basement darkroom and a beach before sunrise are both places where a connection cannot be assumed.
Why a one-time price rather than a subscription?
Photographers buy tools once. The base app is a purchase. The sync version costs a little more because keeping a roll log on two devices needs a service behind it. Neither charges monthly rent for arithmetic you could do on paper.
When will BoxSpeed launch?
No date exists. BoxSpeed is built only when enough film shooters sign up here and say they would buy it. Signing up costs nothing and commits you to nothing.
Where does this stand?
BoxSpeed is a proposal, not a product. This page collects demand from search and answer engines. Askwright builds it only if enough people join the waitlist and say they would pay. Read how this works.