Apertia · Library
What scene measurements are needed before solving a near-to-far focus plan?
Survey near and far edges before a shot plan: 1000–1100 mm needs f/4.4, but a front edge at 950 mm moves focus to 1019.215 mm and the aperture to f/7.014.
What the shot planner solves
Apertia's shot plan asks two questions: the nearest sharp point and the farthest sharp point, measured from the sensor plane, with Infinity available for the far point. It solves s = 2 × Dn × Df ÷ (Dn + Df) for the focus distance and N = f² × s × (1/Dn − 1/Df) ÷ (2c × (s − f)) for the aperture, iterating the image distance until the sensor-plane conversion settles. For an infinite far point it uses s = 2 × Dn and N = f² ÷ (c × (2 × Dn − f)).
The answer is then rounded up to the next third-stop on the app's aperture list. If that stop passes the planner's single-frame diffraction limit, the plan becomes a focus stack instead. The quality of the answer depends entirely on whether the two distances you typed really are the outer edges of what must be sharp.
Worked example
This example covers measured detail boundaries at 1000 and 1100 mm. If an actual required edge lies nearer than 1000 mm, the original input no longer describes the whole task.
- Focus distance for the stated detail boundaries (mm)
- 1047.493368
- Continuous required f-number
- 4.421582
Measure the edges, not the centres
- Fix the camera position and framing first; the survey only holds for that composition.
- Find the nearest surface that must be sharp, such as the front edge of a product, and measure it from the sensor plane.
- Find the farthest required detail; choose Infinity if it is the horizon.
- Enter both in the plan and read Focus at, the aperture and the Sharp from … to … line.
Worked example: a missed front edge
With full frame and 50 mm, a target from 1000 to 1100 mm gives a focus distance of 1047.493 mm and a required f/4.422, rounded to f/4.5. If the product's front edge actually sits at 950 mm, the same far point gives focus at 1019.215 mm and f/7.014, rounded to f/7.1 — more than a stop smaller. A landscape from 3000 mm to Infinity needs f/14.247, rounded to f/16, which exceeds the full-frame single-frame limit, so the plan switches to a stack at f/11.
- 1000–1100 mm
- focus 1047.493 mm · f/4.5
- 950–1100 mm
- focus 1019.215 mm · f/7.1
- 3000 mm–Infinity
- stack at f/11
Common mistakes
- Measuring to the centre of a bottle instead of its front edge and getting an aperture that misses the label edge.
- Typing 100000 mm for the horizon instead of choosing Infinity.
- Changing the framing after the survey but keeping the old distances.
What the plan cannot know
The planner solves only the geometry you describe. It does not detect an unmeasured foreground leaf or decide which detail matters. The DOFMaster equations linked below are the source of the near and far relations the plan inverts.