Apertia · Library
Which changes between frames can invalidate a geometrically complete stack?
Tell a moved subject from an uncovered distance in a two-frame 50 mm stack for 1000–1500 mm, where the frames meet at 1198.4 mm at f/8 and 1296.8 mm at f/11.
What the plan assumes about the scene
Each frame in an Apertia stack covers a distance interval calculated for one fixed camera position, one aperture and a subject that stays where it was measured. The plan's coverage depends only on those distances. If a leaf drifts, a reflection shifts or the tripod is bumped between shots, the merged picture can show a soft or doubled band even though every distance was covered.
The useful question after a failed merge is whether the soft band lies at a frame joint or somewhere a frame should have covered. A band exactly at a joint distance can come from a coverage gap; a band at a distance well inside one frame's interval points to movement or a change in the scene.
Review a stack that went wrong
- List each frame's planned near and far limits from the plan.
- Estimate the distance of the soft or doubled area in the merged image.
- If it lies inside one frame's interval, open that original frame and compare it with its neighbours.
- Look for changed position, light or reflections between those frames and note them in the log.
- Reshoot with the subject secured rather than changing the planned numbers.
Worked example: where the joint is
For full frame, 50 mm and a 1000–1500 mm target, f/8 needs two frames: 1000–1198.4 mm and 1198.4–1505.9 mm. Apertia's own plan uses f/11 for this range, also two frames, meeting at 1296.8 mm and reaching 1876.3 mm. A petal that is soft at about 1100 mm sits in the middle of the first f/8 frame, so a coverage gap cannot explain it; the petal moved, or the first frame was not focused where planned. A soft band at about 1198 mm in the f/8 set falls on the joint and deserves a coverage check first.
- f/8 · joint
- 1198.4 mm
- f/11 · joint
- 1296.8 mm
- Soft area at 1100 mm
- inside frame 1
Common mistakes
- Adding frames to fix a band that was caused by wind, not by missing depth.
- Changing aperture between frames to keep shutter speeds short, which changes every interval.
- Learning the method on a live flower instead of a still object.
What coverage cannot detect
A covered plan does not check motion, alignment or lighting, and this guide does not recommend a stacking program. The DOFMaster equations and the University of Arizona camera-systems notes listed below describe the geometry the plan uses.