Originally Posted by
Doremus Scudder
Nope. Base your exposure on the shadow value. Averaging high and low readings can lead to underexposure when the subject brightness range is great. Overexposure if the SBR is small. You measure the highlight to know if there will be a problem there and if you have to adjust development time to compensate. If you never change development time, then you don't even need to meter the highlight; just deal with the contrast when printing. Many do.
Shadows develop completely in the first third or so of development. Highlights keep developing until we stop them. Film is hardly ever developed till it's finished; we stop development when the highlights get to the point we like. Less development = less dense highlights ("pulled" if you like, but I dislike the term). More development = more dense highlights ("push," but...). The shadows don't change much with changes in development; that's why we base exposure on the shadows.
You can get more development by increasing time, temperature, dilution strength, etc. but best practice is to establish a good agitation regime and a standard temperature and simply adjust the time of development to change things. Tweaking agitation can affect evenness of development. Tweaking temperature is a lot less controllable, so stick with time changes.
Doremus
Bookmarks