# 025 — Focus Field

## Problem Situation

Photographers adjust three interacting variables — aperture, focal length, and subject distance — to control what's sharp and what's blurred. But the resulting zone of acceptable focus (depth of field) is invisible. It has a real spatial shape: a volume in front of and behind the focus plane where objects appear sharp. This shape changes dramatically and non-linearly as parameters shift.

Existing tools are calculators. They return numbers (near limit, far limit, total DoF) but give no spatial understanding. A photographer reads "DoF: 8.7cm" without seeing that this means a razor-thin slice at 2.5 meters, or that moving one stop from f/1.8 to f/2.8 nearly doubles the zone, or that stepping back 1 meter triples it.

The parameter interactions are counterintuitive: a wide-angle lens at f/2.8 can produce a deeper field than a telephoto at f/8 at the same distance. Three variables combine, cancel, or amplify each other in ways that tables cannot convey.

## What Was Built

A spatial depth-of-field instrument. A side-view canvas diagram shows the camera, the focus plane, and the zone of sharpness as a visible expanding trapezoid in space. The logarithmic distance scale (20cm to 100m) matches how photographers think about distance. Click and drag to move focus distance directly on the canvas.

Controls: 11 focal lengths (14mm-300mm), 10 aperture stops (f/1.4-f/22), continuous focus distance slider. Five presets (Portrait, Street, Macro, Landscape, Sports) show dramatically different zone shapes. Readings: total DoF, near/far limits, front/behind distribution bar, hyperfocal distance, sensitivity sparklines (DoF vs aperture, DoF vs focal length), and contextual insight text.

## Why This Form

The problem is spatial — the zone of sharpness IS a shape in space. A side-view diagram is the native representation: the camera at left, distance extending right, the zone visible as a region you can see reshape in real time. Calculators give numbers; this gives shape. The cone-of-light metaphor (narrow near the camera, expanding outward) maps naturally to how light actually behaves through a lens.

## What's Interesting

The dramatic visual contrast between presets reveals what numbers hide:
- Macro (100mm f/2.8 at 50cm): 3.2mm of sharpness — a sliver
- Portrait (85mm f/1.8 at 2.5m): 8.7cm — barely covers a face
- Landscape (24mm f/11 at 10m): infinity — everything sharp from 1.5m outward
- The transition between these regimes is continuous and non-linear

The sensitivity sparklines show at a glance which parameter has the most leverage at your current settings — sometimes stopping down helps enormously, sometimes it barely matters.

## Iterations

v1.1: Improved DoF zone visualization with cone-of-light metaphor (blur regions flanking the sharp zone), better label positioning to prevent overlap at narrow zones, focus point glow, and refined camera icon.

## Next Step

Add a comparison mode: lock one configuration, change parameters, and see both zones overlaid. This would make the "what if I stop down?" or "what if I use a longer lens?" question directly answerable by visual comparison rather than mental math.

## Art Direction Note

Dark editorial, monochrome. Default Night Lab direction. The canvas is the primary instrument — controls serve it, not the other way around. JetBrains Mono for all labels and readings. Generous negative space. The darkness makes the subtle zone gradients legible.

## Promotion Candidate Read

Maybe. The form-to-problem fit is strong — spatial information shown spatially — and it genuinely reveals something invisible (the shape, not just the numbers). But the artifact stays within the parameter-space instrument family (017, 021) and is diagnostic-only. Needs comparison mode and possibly real-time photo preview to graduate.
