Image detail has no single number

Image detail has no single number. A sensor can sample a scene finely while motion, focus, lens contrast, diffraction, processing, or crop becomes the active limit. A theoretical cutoff can identify what to test; it does not prove a camera resolves a subject feature.

Use pixel and output arithmetic to understand margin. Use compatible controlled MTF/SFR data only under matched conditions. Then make an actual test at the aperture, focus distance, movement level, processing, and output that matter. A local image inspector can offer bounded evidence about the decoded file, not a system-resolution certification.

Diffraction is a specific and often misunderstood member of this list. The Airy-disk diameter grows with a smaller aperture, and once it exceeds a stated pixel-pitch threshold, diffraction becomes the limiting factor ahead of the lens itself. That threshold is a geometric idealization, not a hard wall: a lens can still show a usable, even excellent, result one or two stops past a calculated diffraction-limited aperture, because sharpening, output size, and viewing distance all interact with the same underlying blur. The calculation tells you when to start paying attention, not when detail disappears outright.

MTF and SFR data carry their own comparison boundary. A number from one test chart, lighting setup, and measurement software is not directly comparable to a number from a different one, even for the same lens. Two curves must share their capture conditions before a comparison means anything, and even then the result describes contrast at specific spatial frequencies under those conditions, not a single "sharpness" grade for the whole system. Sensor pixel count changes what those frequencies mean in absolute terms but does not by itself change how much real scene detail a lens, a focus system, or a moving subject allows through.

Use the Pixel Pitch and Sampling Planner and Sensor Resolution and Crop Planner to establish the sampling and crop margin available. Use the Diffraction and Sampling Tradeoff Planner and Airy Disk and Resolution Target Planner for the aperture-versus-detail question specifically, the MTF and Detail-System Interpreter only when you have matched-condition test data to compare, and the local sharpness diagnostic or print-suitability planner when the question is about one actual decoded file rather than a system in the abstract.

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