Apertia · Library
What does an incomplete forty-frame stack mean?
See what Apertia's 40-shot cap means: a 100 mm f/2 stack from 500 mm stops at 554.857 mm, while the same 500–2000 mm range closes in 39 shots at f/11.
Why the planner stops at forty
Apertia builds a stack frame by frame: each new focus distance is chosen so that its near limit equals the previous far limit, and the loop ends as soon as a far limit reaches the farthest sharp point. It also ends after 40 shots, whatever has been covered. The plan then lists forty shots without a separate warning, so the last shot's far limit is the only sign that the target was not reached. The library's stack calculator reports the same case explicitly, with the uncovered range.
Close subjects and wide apertures make each frame very thin, so the cap is reached long before the far target. In the app's own plans this is rare, because a stack is always planned at the stack aperture for the sensor, f/11 on full frame.
Worked example
The 100 mm full-frame model at f/2 advances from a 500 mm near target through forty frames but reaches only about 554.857 mm. The requested 2000 mm far target remains uncovered.
- Target fully covered
- No
- Frame cap stopped the sequence
- Yes
- Uncovered range begins (mm)
- 554.857454
- Requested far target (mm)
- 2000
Check a long stack
- Write down the near and far target before reading the shot list.
- Count the shots; forty is the cap, not a coincidence.
- Compare the last shot's far limit with the far target.
- If it falls short, save the uncovered interval with the plan.
- Change the setup — aperture, distance or target — rather than calling the remainder sharp.
Worked example: 100 mm from 500 to 2000 mm
At f/2 on full frame, the first frame covers only 500 to 501.142 mm. After forty frames the sequence has advanced to 554.857 mm, with the fortieth shot focused at 554.036 mm; 1445.143 mm of the requested range remains uncovered. At f/11, the stack aperture Apertia's planner uses on full frame, the same range closes in 39 frames, the last focused at 1975.489 mm and reaching 2091.47 mm — one frame inside the cap.
- f/2 · after 40 frames
- reaches 554.857 mm
- f/2 · still uncovered
- 554.857–2000 mm
- f/11 · frames to cover
- 39
- f/11 · last far limit
- 2091.47 mm
Common mistakes
- Reading a forty-shot list as complete because the number looks deliberate.
- Splitting the target into two plans and forgetting to check the joint between them.
- Opening the aperture to shorten exposures without re-reading how far the stack now reaches.
What the cap does not tell you
The cap is a stopping rule of the planner, not a recommendation about how many frames a stacking program can handle. The DOFMaster equations listed below give the thin-lens limits each frame uses.