For the past weeks I´ve been reading posts that discuss different film, exposure index and developing combinations, giving single films different speeds, according to these combinations. I understand that any given film has a given light sensitivity, depending on silver grain size, shape and distribution. That would imply that each film has a single threshold that defines its "speed." Wouldn´t this mean that any attempt to push the film - meaning to move the light sensitivity threshold further down - is only going to produce underexposed and overdeveloped images ? The only thing it seems to achieve is pushing the mid-range of tones further up the straight portion of the curve, but you are not really making film faster, in terms of requiring less light for the same tonal scale. Are there really developers that can produce a visible image from a latent image that received too little energy to react with the normal developing agents ?