Ilford Delta 400

Original (datasheet-validated). See the notes, the B&W README, and the Knowledge base.

The film

Ilford Delta 400 Professional, a fast, fine-grain B&W film on the same core-shell tabular (T-grain) crystal technology as Delta 100 and Delta 3200, positioned by Ilford as "ideal for action and available light photography" while also giving "fine grain results for pictorial and fine art photography." The datasheet (archived: _reference-sources/datasheets/ilford/delta-400.pdf, Nov 2018) states an ISO 400/27° speed rating measured in ID-11, with the manufacturer explicitly sanctioning use "at meter settings up to EI 3200/36... given extended development" in four named developers.

Why this was a gap worth closing

Like Delta 100, this stock sat flagged as a ❌ derivation candidate in the notes with its datasheet already archived (fetched 2026-07-15) but never actually read into a recipe. Extracting the primary source turned up a specific, citable number worth having: a real contrast target rather than a speed rating.

The number that grounds this recipe: Gbar 0.62

Ilford's own development-time table states plainly: "The times in bold will produce negatives of normal contrast (Gbar 0.62)." Gamma-bar is a standard sensitometric measure of average development contrast, a firmer, more precisely specified target than most datasheets in this bank provide. That number, not a stylistic guess, is what justifies this recipe running a notch firmer (Highlight —/ Shadow —) than HP5 Plus 400's more forgiving — / Shadow —. Two 400-speed Ilford stocks, two different documented contrast philosophies.

T-grain vs conventional grain, at matched speed

This is the same real distinction found in the Delta 100 knowledge file, just at 400-speed instead of 100: tabular crystals present a flatter, more regular boundary to light than the conventional (cubic) grain in HP5, which is the physical reason T-grain emulsions are documented to read finer and hold higher acutance at a matched box speed. HP5 remains the "classic latitude" choice; Delta 400 is the "modern precision" one. Both are legitimate, and they are genuinely different films, not two labels for the same recipe. See film-chemistry-fundamentals.md.

The grade in one line

A 400-speed B&W that spans daylight to available-light on its own datasheet's terms (EI 200–3200 in a single film), with a firmer, better-specified contrast target than its "balanced and forgiving" sibling HP5.

vs the rest of the B&W family

See the comparison table in the Delta 100 knowledge file for the full seven-stock picture.

Validation status

Datasheet-validated (EI range, T-grain construction, the Gbar 0.62 contrast target, archived PDF). Characteristic pass strong (T-grain vs conventional-grain behaviour is widely documented and consistent with independent film reviews). No real-film scan obtained yet. Drop one into references/, ideally at a pushed EI to test the recipe's —/ISO—headroom against real push-development grain and contrast.