Apertia · Library
How do you check coverage after rounding a calculated aperture to a real stop?
After the shot planner rounds a continuous f-number such as f/7.18 up to f/8, recheck near and far limits at that stop before you trust the plan.
Why the planner rounds upward
Apertia's shot plan solves for the exact f-number that makes your nearest and farthest sharp points meet the circle of confusion. That answer is continuous, so the planner then picks the first value at or above it from its list of full and third stops, from f/1 to f/32. It rounds toward the smaller opening because a larger f-number can only widen the geometric depth of field when focus, focal length and sensor stay the same.
The rounded stop is then checked against the planner's diffraction rule. If it is larger than the half-CoC limit for the sensor (f/11.18 on full frame), the plan stops offering a single frame and proposes a focus stack instead. A requirement above f/32 has no stop at all, and the plan goes straight to stacking.
Worked example
Covering a 1000–1100 mm target range with the 50 mm full-frame model requires about f/4.422. The model rounds to f/4.5. A camera that offers a different stop still needs its own explicit recheck.
- Continuous required f-number
- 4.421582
- Next model stop
- 4.5
- Planned sensor-plane focus distance (mm)
- 1047.493368
Recheck a rounded plan
- Enter the nearest and farthest sharp points in Shot plan, using distances from the sensor plane.
- Read the continuous requirement and the stop the plan shows under Aperture.
- Set that stop and the plan's focus distance in the calculator, with the same kit.
- Compare the calculator's Near and Far values with the two points you asked for.
- If your lens cannot set that stop, choose the next stop it does offer and repeat the comparison.
Worked example: 35 mm, 1.5 to 3 m
With a 35 mm lens on the full-frame preset and a request from 1500 mm to 3000 mm, the exact solution is f/7.183. The list has f/7.1 and f/8, so the plan shows f/8 and a focus distance of 1996 mm. Setting f/8 at 1996 mm in the calculator gives a near limit of 1459.1 mm and a far limit of 3183.3 mm, which contains the requested range with a little room on both sides.
A tighter request behaves differently. With 50 mm and 600 mm to 1000 mm, the requirement is about f/34.77, beyond f/32, so no stop exists and the plan proposes 4 frames at f/11.
- Exact requirement, 35 mm, 1500–3000 mm
- f/7.183
- Stop shown by the plan
- f/8
- Near and far at f/8, focus 1996 mm
- 1459.1 mm – 3183.3 mm
- 50 mm, 600–1000 mm
- 4 frames at f/11
Common mistakes
- Setting f/7.1 because it is closer to f/7.183. It is below the requirement, so one end of the range can fall outside the limits.
- Changing the focus distance after rounding. The coverage check only holds for the distance the plan returned.
- Assuming every lens has third stops. Some lenses offer only full stops, which can push the choice from f/8 to f/11.
- Forgetting that a stopped-down plan also needs more light or a longer exposure.
Where the check ends
The stop list is the app's planning list, not a record of what your lens can set. The DOFMaster equations listed below are the same thin-lens relations the check uses, so a real lens can still differ, especially close up.