Is there a general rule regarding the effect on grain, sharpness and film speed from increasing the dilution of a developer -- for example, using Microdol-X 1:1 or 1:3 instead of straight?

-- Ben Crabtree (bcrabtree@mn.rr.com), April 22, 2002

Answers

In theory- a diluted developer will give higher sharpness, more grain, and higher speed than the same developer @ full-strength. But this is a complicated topic: the possible effects are almost infinitely varied; and variations in individual procedure can provide different answers than expected. By far the best discussion of these issues is in "The Film Developing Cookbook", by Anchell & Troop. published by Focal Press. Very highly recommended!

-- Mark Sampson (MSampson45@aol.com), April 22, 2002.

The theory (which Mark mentioned) - assumes the developer is high in solvent effect and physical development. On the other hand, FX-1 type developers don't have either of these and the effect will be different. Properly formulated ascorbic acid developers are interesting because in some aspects they resemble physical development yet visual sharpness can be very high. If poorly buffered developers are combined with chemically-hungry films at a large dilution ratio, the working pH of the solution drops very quickly and this adds another effect. On the other hand, well buffered formulae are more stable in this effect. I think it is better to say there is no general rule for dilution.

-- Ryuji Suzuki (rsuzuki@rs.cncdsl.com), April 22, 2002.

I agree with both the posts above, but I will add a few specific examples. Developers that contain solvent chemicals reduce the apparent grain by physically dissolving the edges of the grain, but this solvent action reduces apparent sharpness. The primary solvent chemical in most developers is sodium sulfite. Sodium sulfite has many beneficial effects (other than dissolving the grain), which is why most developers contain at least some of it in their formula.

Developers with fairly high amounts of sodium sulfite include D-76, XTOL, and Microdol-X (and the equivalent formulas from Ilford and others). When used as a straight stock solution (undiluted) these developers have a definite grain reducing and sharpness reducing effect. When used 1:3 dilution, the percentage of sodium sulfite is reduced and there is much less effect on grain or sharpness other than what is inherent in the film. Intermediate dilutions such as 1:1 or 1:2 are often used as a compromise.

Developers such as HC-110 and Rodinal have little or no sodium sulfite (depending on who you ask) and are considered to be among the best for obtaining the sharpest looking negatives. However, Rodinal is also fairly high in alkalinity, which has a tendency to cause grain clumping, which is perceived as an increase in grain (as opposed to merely grain neutral). But when Rodinal is highly diluted (1:50 or above dilutions) the alkalinity is reduced and the grain clumping is significantly reduced.

When used in higher dilutions, Rodinal has a somewhat compensating effect (contrast reducing), has excellent sharpness, and has a minimal grain clumping tendencies. When using Rodinal, it is important to observe other techniques to minimize grain clumping such as constant temperatures of all chemicals. I personally think that developing in temperatures at 70F or lower helps to keep grain clumping in check, but others may disagree. However, grain clumping tendencies vary by the film used, for example Kodak TMAX films and Ilford Delta films are much less sensitive to grain clumping than most older emulsions.

-- Michael Feldman (mfeldman@qwest.net), April 23, 2002.

Actually, there is a lot more to what Michael wrote. One role of sulfite in some developers is said to regenerate developing agents like hydroquinone, which in turn regenerate the other superadditive agents like phenidone. In this mechanism, lower concentration of sulfite may drive the result to higher accutance (by promoting the local exhaustion of developing agents) but has little to do with solvent effect or physical development. By the way, what physical development usually means is deposition of dissolved silver halides on developed metallic silver grains, but not the dissolution part.

But these are rather controversial topics and I recommend not to try to generalize too much by putting together and stretching what people say.

-- Ryuji Suzuki (rsuzuki@rs.cncdsl.com), April 23, 2002.