Z-Stop

Expose for the shadows, develop for the highlights. Z-Stop is an iPhone spot meter true to this Zone System principle. Shoot black-and-white film with the Zone System, no external meter needed. [ Sound familiar? ] - Your mechanical or MF camera has no meter, so you carry a separate spot meter. - You meter with a DSLR, then copy the values to your film camera. - You metered a shadow, shot at that value, and the picture came out too bright. - By the time you develop, you can't remember where you metered. Meter one shadow with your iPhone, and Z-Stop shows the shutter speed and aperture that place it on Zone 3, in ½-stop steps. With Pro, one tap on "Save" keeps the scene as a record image. [ The Zone System ] Set out by Ansel Adams and Fred Archer around 1940, it divides tones from black (Zone 0) to white (Zone 10) into 11 steps. One zone is one stop. Zone 3 is the darkest shadow with full texture: dark clothing, bark in shade. Zone 5 is middle gray: an 18% gray card. The rule: expose for the shadows, develop for the highlights. [ A meter only tells you Zone 5 ] Any reflected-light meter gives the exposure that renders the metered spot as middle gray (Zone 5). Meter a shadow and shoot at that value, and the shadow turns gray. To place it on Zone 3, give 2 stops less, measured on that one spot. That is why you need spot metering. [ What Z-Stop does ] * Spot metering on your iPhone - Measures only inside a small circle on the screen. * Checks the shadow - A green "Z3 OK" if the spot is even enough to use, a red "Re-meter" if pattern or edges are mixed in. * Finds a spot for you - "Find Zone 3" marks usable spots. With no Zone 3 it looks for Zone 4, and with neither it says "Don't shoot." * Does the math - Takes off 2 stops and converts to your body's shutter steps and your lens's aperture range. - If a step can't be set, the warning tells you what to change (e.g. Open the aperture · Remove the ND). * Five steps for half-stop differences - From the reading down to -2 stops in ½ stops. - Full-stop shutters: missing steps are grayed out, and "By aperture" splits them by aperture. * Keeps a record (Pro) - The record image keeps the scene, readings, shutter and aperture in the same layout as the metering screen. * Previews black-and-white tones [ How to use ] 1. Tap a dark spot, or tap "Find Zone 3" at the bottom left of the camera view and tap a circle. The circle becomes the reference right away. For a spot you metered yourself, tap its green "Z3 OK" box. 2. Five steps appear (+1 to -1 stop with a Zone 4 reference). 3. -2 stops is the theory; the right step shifts by about half a stop with film, EI and development. For your first roll, shoot -2 · -1.5 · -1 stops. After developing, the frame where the Zone 3 shadows show their shapes is your chosen frame. 4. With Pro, tap "Save" at the bottom left of the camera view. The record image goes to the "Z-Stop" album in Photos. [ Free and Pro ] Free: metering, Find Zone 3, the five steps, By shutter, By aperture, B&W preview and all settings. Pro (yearly subscription) unlocks saving record images. [ Also ] Setup: body, EI, aperture, lens (max and min aperture), ND, EV calibration. Find your body in "How to choose a body". Privacy: no network use except Apple's subscription check, no ads or analytics, video stays on your iPhone. Terms of Use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/ * A reflected-light meter based on the iPhone's main camera. Development (highlights) is up to you. * Before important shoots you can't redo (weddings, trips, paid work), always test first with a roll or two to set your EI and chosen frame.