I have compared Pyrocat-HD to D76 1:1 (and to PMK) but not with Thornton's 2-bath metol formula. The comparison with D76 involved both tests for resolution in lppm, using a standard Air Force resolution chart, and a visual comparison of prints 20X24" in size from 4X5" comparison negatives. My conclusion was that PMK and Pyrocat-HD negatives were virtually identical in sharpness and resolution, and both were significantly better than D76 1:1 in both categories.
Originally Posted by skahde
With regard to sharpness let me add that with many developers it is highly dependent on type of agitation. With Pyrocat-HD in particular negatives developed with rotary agitation tend to be not quite as sharp as those developed with minimal agitation.
Assuming, however, that we could improve on the Pyrocat-HD formula in terms of the rendition of fine detail for 35mm or roll film work I would suggest two possible approaches. 1) Reduce the amount of phenidone by about 50%, or 2) replace the phenidone with metol at the rate of about ten parts metol to one part phenidone. Phenidone has great regenerative qualities and if there is too much of it in the formula the result will be a loss of sharpness from reduced adjacency effects. So either reducing the amount or substituting metol could provide slightly sharper results. I would speculate, however, that the method of agitation would continue to play an important role in apparent sharpness irrespective of these changes.