Support
T-Stop Pro is a photometric exposure calculator for cinematography. You pick a fixture from the catalogue, set the distance, colour temperature, any modifiers or gels and your camera settings, and it gives you the illuminance and the resulting T-stop at your subject.
Getting help
Email is the support channel, and it reaches a person rather than a queue:
T-Stop Pro is made by one person, so expect a reply in a few working days rather than within the hour. Every message is read.
To get a useful answer faster, include:
- your device and iOS version;
- the fixture you were working with, by manufacturer and model;
- what you expected and what you got, with the numbers if you have them;
- a screenshot, which is usually worth more than a paragraph.
Report a wrong or missing fixture
This is the most valuable message you can send, so it gets its own section. The catalogue grows and gets corrected because working cinematographers report what they find on set, and every report is looked at against the manufacturer's own data.
Send it to james@tstoppro.com with "fixture" in the subject line.
A fixture is missing
- manufacturer and exact model name, including the variant;
- a link to the manufacturer's photometric data or a photo of the printed spec, if you have one to hand. The maker's own datasheet is what we work from.
A fixture's numbers look wrong
- the fixture, and the exact settings you had in the app: distance, colour temperature, mode, beam angle, and any modifier or gel you had selected;
- what the app said, and what you measured;
- which meter you used, and where you put it.
Real disagreements between the app and a meter are useful even when the app turns out to be right, because they usually point at a gap in the published data behind a fixture. Please send them.
Common questions
Where does the photometric data come from?
Primarily from data published by the fixture manufacturers themselves: photometric tables, datasheets and spec posters. Where a manufacturer publishes several measured distances or several colour temperatures, those are stored as they were published, and the app interpolates between them for the distance and colour temperature you actually asked for. A manufacturer's numbers are never expanded into extra invented datapoints.
Why doesn't the app match my light meter?
T-Stop Pro produces estimates, not measurements, and it is not a substitute for metering on set. Lamp age, supply voltage, dimmer curves, firmware, bounced and ambient light, lens and filter transmission, sensor calibration and unit to unit variation all move the real answer, and the manufacturer data underneath can itself contain errors or omissions.
Verify critical exposure with a meter and a test. See section 4 of the Terms for the full statement.
That said, a large disagreement is worth reporting. Please tell us about it.
Does it work without a signal?
Yes, once it is set up. The app keeps its own copy of the fixture catalogue on the device and calculates entirely on the phone, so a stage with no bars, a basement or a plane are all fine.
Two things do need a connection, so get them out of the way before you leave: signing in, and the first download of the catalogue. A brand new install has no fixture data until it has been online once. After that you are independent of the network until you want to pull down updates.
How do I get new and corrected fixtures?
Open the menu from the top left of the calculator screen and tap Sync. It re-fetches the current catalogue and replaces the copy on your device. The app also refreshes quietly in the background when it starts, so Sync is what you reach for when you want a change now, or when you have just been told a fixture has been added or fixed.
You do not need to reinstall the app or wait for an App Store update to get catalogue changes. Reinstalling is not the way to refresh the data; Sync is.
What does the calculation actually take into account?
Two separate stages, and it helps to know which is which. First, the fixture: its published output, the distance, the colour temperature, and the fixture's own options such as mode, beam angle, voltage or lamp, give the illuminance. Second, your camera: frame rate, ISO and shutter angle, along with any modifier and any gels you have stacked, turn that illuminance into a T-stop.
Camera settings never change the illuminance itself. Illuminance is what is falling on the subject; the camera only decides what stop it comes out at.
You can also work backwards: set the T-stop you want and the app solves for the distance that gives it.
How do I delete my account?
In the app, open the menu, tap Account Settings, and use Delete Account at the bottom of that screen. It asks you to confirm, then removes your sign-in, profile, registered notification devices and server-side account data. It clears saved setups and cached account data from the requesting device; other devices are signed out when they next connect. It cannot be undone.
Apple and RevenueCat may continue to process purchase and subscription records for billing, restoration and refunds. A minimal one-way deletion record prevents old services from recreating the account. The full deletion, backup and retention boundary is in the Privacy Policy.
Deleting the account does not cancel or refund an Apple subscription. Cancel it separately in Apple Subscriptions if you do not want billing to continue.
If you cannot reach the in-app option for any reason, email james@tstoppro.com and the deletion will be done for you.
I bought an unlock and the app is not showing it
Start by checking the obvious one: that you are signed in to T-Stop Pro with the same account you used when you bought it, and, for anything bought inside the app, that the device is signed in to the same Apple ID. A purchase follows the account it was made on, so signing in as somebody else is the usual explanation.
If it still does not appear, email james@tstoppro.com with the email address on your T-Stop Pro account and, if you have it, the App Store or payment receipt. It will be put right by hand.
What does Lifetime Pro include?
Lifetime Pro includes the Pro calculator tools and ongoing catalogue updates, with one payment and no renewal. Optional AI services, if introduced later, would be priced separately. You do not need an AI subscription to keep your Lifetime Pro calculator, and cancelling an AI subscription would leave that access intact. Features and access already promised with an earlier purchase are preserved.
How do I cancel or get a refund?
Anything bought inside the app is bought from Apple, and Apple handles cancellations and refunds for those purchases: cancel a subscription in your Apple ID settings and request a refund through Apple. We cannot reverse an App Store charge. No direct web checkout is currently available on tstoppro.com. The details are in section 7 of the Terms.
Does the app track me?
The current app release includes an optional PostHog analytics library, but T-Stop's product-usage collection is disabled. It contains no crash-reporting, advertising or tracking SDK. Your calculations, the fixtures you look at and the setups you save are not sent to us for analysis. The full detail, including what the website does differently, is in the Privacy Policy.
Is there an Android version?
The first release is being prepared for iOS. Android is planned as a future beta; join the waitlist for updates.
I have a feature request
There is a public board at feedback.tstoppro.com, which is also where the Feedback button in the app menu takes you. Post it there so other people can add their weight to it, or email it if you would rather not post in public.
A short note about the problem you are trying to solve is more useful than a description of the feature you have in mind.
Legal
Privacy Policy · Terms of Service
T-Stop Pro is provided by James Coote. Fixture names, model numbers and manufacturer brands appear in T-Stop Pro for identification only, and T-Stop Pro is not affiliated with or endorsed by any fixture manufacturer.