Acutance Developers

A popular developer very many years ago was a simple metal-sulphite-carbonate solution which is commonly known as the Beutler formula. It is used at a dilution of 1: 10 as a one-shot developer, times of 7 -10 minutes were average, giving soft and finely-detailed negatives. This effect became known as acutance or the adjacency effect or more simply, high definition. It makes the image look sharper. The extra sharpness is an illusion. The Beutler developer and the many later formulations under the acutance or high definition label make use of the adjacency effect to present greater visual sharpness, although the actual resolution of fine detail might be lower than that produced by the orthodox developer. Acutance developers rarely contain a restrainer because it is considered that such an addition would inhibit the adjacency effect. Nevertheless, alternative formulae by Geoffrey Crawley use potassium iodide in minute quantities. It is used once only at 200 C, FX-1 gives development times of 12-15 minutes. Effective film speed is said to be increased by 1; 2-1 stop. There are many branded acutance or high definition developers and they have a valid use. They are not formulated for general purpose working. They are not fine grain developers. Ideally, they are for use with inherently fine grained films of a lower rated speed than ISO 100/210 and with first class lenses on both camera and enlarger. Exposure and processing must be exact.