ISO Priority pin
Pin ISO and let aperture and shutter both vary; not yet wired.
Summary
Planned third priority mode that pins ISO at your loaded film speed and lets the solver vary both aperture and shutter to match scene EV. Useful when you want to express creative preference for a depth-of-field/motion combination without locking either axis hard.
How it works
Current limitations
The ExposurePriority enum today has APERTURE and SHUTTER values only. The solver has dedicated branches for both: APERTURE holds f-stop and computes a shutter to match metered EV; SHUTTER holds shutter and computes an aperture. Neither branch supports a pinned ISO with both other axes free.
What's planned
Add ExposurePriority.ISO and a corresponding solver branch that holds the loaded film ISO and computes a balanced aperture/shutter pair using configurable preferences (e.g., 'prefer shutter near 1/125' or 'prefer aperture wider than f/5.6'). Surface a chip in the priority picker on the Viewfinder so you can pin ISO and let the meter pick a sane combination on its own.
Why it is LOW priority
Film ISO is functionally pinned already once you load a roll; you cannot change it mid-roll. The user value of an explicit ISO Priority mode is mainly clarity (the UI confirms what is locked) and gives the solver a place to express paired aperture/shutter preferences for a stock you are committed to.