How long is a flat good for?
An epoch is the stretch over which one flat still corrects your lights. It ends whenever the optical response changes, whether you did it on purpose (collimating, cleaning, re-spacing) or found it later (a dust mote arriving, moving, or clearing, a shift in vignetting or illumination). Flats from before the change stop matching lights taken after it.
Routine camera rotation between targets usually does not end an epoch. Mark a boundary only if a rotation visibly shifts the vignetting.
Marking a boundary
Section titled “Marking a boundary”EigenFrame watches your flats over time and can flag a night as a Boundary candidate when its flats look like the optical train shifted rather than like a passing cloud or dew. That flag shows up on the flat verdict banner with a Mark optical-train change button next to it.
Marking one is always something you confirm. EigenFrame never creates a boundary on its own, whether it noticed the change itself or you spotted it by eye on the flat timeline. You can also open the rig logbook directly and mark a change between two nights yourself, with your own note describing what happened.
Screenshot: Flat verdict banner showing a boundary candidate and the Mark optical-train change button.
What marking one does
Section titled “What marking one does”A flat from before the boundary is never assigned to a light from after it, no matter how close the two dates are. The boundary is absolute: date proximity alone never overrides it.
Why this matters day to day
Section titled “Why this matters day to day”You need one validated flat master per epoch per filter, not one per session. A flat from a nearby night inside the same epoch is a normal, healthy assignment, and calibration assignment prefers exactly that: among the flats inside a light’s epoch, the nearest night wins.
Where epochs show up
Section titled “Where epochs show up”The flat timeline for a rig groups nights into epoch bands, with each optical-train change marked between the nights it separates. This is the place to scan a rig’s flat history and see when the field actually shifted.
Screenshot: Flat timeline for a rig with epoch bands and a boundary marker between two nights.
The viewer’s Calibration tab shows the same boundary at the level of one light: its ranked list of candidate flats marks any that sit on the far side of an epoch boundary, and the best in-epoch flat carries a star.