Apertia · Library

How do you choose a supported aperture without treating the stop list as lens specifications?

Apertia's planner uses third stops from f/1 to f/32; a requirement of f/11.09 jumps to f/13 and, on full frame, turns a single frame into a two-shot stack.

The list behind the aperture ring

The calculator's aperture ring and the shot planner share one list of 29 values: f/1, 1.1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.5, 2.8, 3.2, 3.5, 4, 4.5, 5, 5.6, 6.3, 7.1, 8, 9, 10, 11, 13, 14, 16, 18, 20, 22 and 32. Full stops get the long marks and labels on the ring; the rest are third stops. There is nothing between f/22 and f/32, and nothing above f/32.

When the planner needs a setting, it takes the first listed value at or above the exact requirement. That rule interacts with the diffraction limit: on full frame a single frame is allowed only up to f/11.18. A requirement just above f/11 therefore rounds to f/13, crosses the limit and produces a stack, even though the exact value was below the limit.

Worked example

This setup requires about f/4.422 in the model and proposes f/4.5 from its stop list. A real lens still needs to support that setting and the resulting photograph still needs checking.

Continuous required f-number: 4.421582
Proposed planning stop: 4.5

Read a plan against your own lens

Note the exact requirement and the stop the plan selected from the list.
Check whether your lens offers that stop; many lenses and some cameras use half or full stops.
If the plan shows a stack, read the stack aperture instead, which is the largest listed stop at or below the half-CoC limit.
For a lens that lacks the stack aperture, use its next wider stop and recheck every frame's limits in the calculator.

Worked example: crossing the limit by rounding

With 50 mm on full frame, asking for 1000 mm to 1290 mm needs f/10.808. The next stop is f/11, which is under the 11.18 limit, so the plan keeps one frame focused at 1126 mm; the calculator confirms 998 mm to 1293 mm at f/11. Stretching the far point to 1300 mm raises the requirement to f/11.089. The next listed stop is f/13, so the plan switches to 2 frames at f/11: one focused at 1128 mm covering 1000–1297 mm, and one at 1532 mm covering 1297–1876 mm.

Request 1000–1290 mm: f/10.808 → f/11, one frame
Request 1000–1300 mm: f/11.089 → f/13, stack
Frame 1: 1128 mm (1000–1297 mm)
Frame 2: 1532 mm (1297–1876 mm)

Common mistakes

Treating f/25 or f/29 as available because a lens shows them. The planner's list jumps from f/22 to f/32.
Expecting a small change in the far point to change the plan only slightly; crossing a stop boundary can switch it to stacking.
Using the single-frame stop when the plan has switched to a stack. Stack frames are calculated at the stack aperture.
Reading a missing stop as an error. A requirement beyond f/32 simply has no single-frame setting.

What the list is not

The values are a planning convention taken from common lens markings. They do not say which stops your lens supports or how accurately it sets them, and the DOFMaster and University of Arizona references below describe the model, not any particular lens.