Developing By Inspection
Developing by inspection is a method of developing B&W film that dates back to the earliest history of light sensitive emulsions. It is the way they used to do it before Ansel Adams and his contempories came up with the zone system, with its standardised methodology.
In short, the film is inspected under a very dim safe light during development to assess the density of the highlights. Development is ceased when the highlights are visible.
Some flesh on the skeleton:
1. Assess the subject as per your normal zone system method, checking for contrast that may exceed the film’s range or not fully utilise it. Expose the film as per your normal guidelines. During exposure we still need to visualise the contrast range of the scene and allow for it by over or under exposing to suit.
If the scene is very contrasty, a little over exposure will allow the shadows to develop relatively earlier. This means that when the highlights indicate that the negative is ready to be removed from the developer, shadow detail will be present.
If the scene is too flat, underexposure will allow the contrast to be stretched during development.
2. In the darkroom, develop in trays, about five or six sheets at a time. At about two thirds of the expected development time, turn your safelight (Wratten #3 or Ilford 908 with 15 watt bulb) on for about 10 seconds and inspect your films’ non-emulsion side. If you can make out the highlights (they’ll be black of course) then the film is done and can be removed into a water bath. Otherwise keep going, checking every minute or so. (Using a water bath prevents back contamination of the developer with stop bath).
I wouldn't want to give any one sheet more than about 40 seconds
under the safe light, but the allowable time does vary with the length of time
the film has been in the developer. The act of developing the film desensitises
the emulsion to further exposure, so after two thirds of the expected development
time fogging is less likely.
3. When all sheets are in the water bath, transfer them to the stop bath and process as per your normal methods.
For me, the biggest advantage is the absence of interminable testing and calibrating of my systems. It doesn’t make much difference if my shutter on one lens is half a stop out, or if my developer is a little old, or if I am using a new brand of film, or I haven’t got my temperatures spot on. It doesn't even matter if I mix N+1 , N and N-1 films together. The film comes out of the developer when the highlights have had enough development to give me a good negative.
I’d rather spend my time shooting than testing. By using this method, I found that my negatives previously had been under-developed, and now are much easier to print. I thoroughly recommend the system for B&W sheet film.
Developing by inspection does indeed free us from the tedium of endless testing, but it doesn't change the way film behaves in light or in the developer. We still have to over and under expose the film and pull/push the developing to control contrast. The difference is that we can control the amount of development by visual means rather than by numbers.
The method really is adhering to the adage “Expose for the shadows, Develop for the highlights”.
I suggest that you read more information if you are interested in applying the technique. It can be found on Michael Smith’s web page at this link and on Ed Buffaloe’s web site at this link