what is force devolopment?

[Abdul Rahman Jamous]

Hi guys hope that you are doing FANTASTIC!

 

I am reading a book called "Master of Light" 

 

in an interview with Owen Roizman, he mentioned a term called force-develop, I wonder what is it?

 

[Mark Dunn]

It's over-development of the negative to increase the sensitivity; another term is "push processing". In that period it was very unusual- Kodak didn't like it and wouldn't offer any sort of assurances if it was done. There were no faster neg stocks until later- I think Fuji A250 was the first; we used it at college in 1981. Kodak was then forced to follow suit.

Another famous example of push-processing is "Barry Lyndon".

[David Mullen ASC]

The sensitivity isn't actually increased since that's determined by the size of the silver halide grains, the larger ones receive more light.

What push or force processing does is increase density of the developed image (the amount of silver halides that get converted to silver); this is usually done in combination with underexposure (in order to shoot in lower light levels).

Underexposure and normal development results in a "thin" negative so by push-processing, you are increasing the density somewhat back to "normal" so that it uses printer lights that are closer to "normal" for making the print.  However, since sensitivity is not actually increased, when underexposing, the slower smaller grains do not get enough exposure and thus get removed in the processing, leaving only the larger faster grains. 

So push-processing just takes the information that got recorded and gives it more density on the negative. The result tends to be a grainier image (more from the underexposure) plus an increase in contrast (because you lost some shadow detail from underexposing) but an increase in base fog level, so the blacks are less black and sometimes have a color cast.

The success of push-processing is somewhat determined by your exposures -- for example, if you underexpose by 2-stops but push-process by 1-stop, the resulting density is still 1-stop under "normal" and the graininess will be higher from the 2-stop underexposure.  But if you underexpose by only a 2/3-stop but push by 1-stop, your resulting density will be slightly higher than normal and the graininess will be milder from the more minimal underexposure (compared to more underexposure.)