contrast range in zone system

[Saganich]

In any zone system thinking the point is to previsualize the final print which means that the highlights and shadows that your measuring are appropriate for your vision of the final print. Which highlights are important, and which can you ignore? I've also found I do not like compensation when processing and prefer full development.

[Christopher Walrath]

Or you could preexpose your negs to bring up the shadow values to recude contrast in the negative.

[pierods]

Originally Posted by Christopher Walrath

Or you could preexpose your negs to bring up the shadow values to recude contrast in the negative.

What do you mean exactly?

[rob champagne]

Both film and paper have a threshold point which requires a certain minimum amount of exposure before anything registers on the film or paper.
For printing there is technique called flashing which you should find plenty of information about if you search the forums.
Pre exposure of film is the same as paper flashing except that paper flashing effects the paper highlights whereas film flashing effects the shadows.
How it works. You give the film an exposure of an evenly illuminated subject. It could be a piece of white card or a grey card or a dark grey card. It doesn't matter as long as the colour is neutral. You expose at a low zone such as zone 1.
You then use the same frame to expose a high constrast subject. Say it has 13 stops of range from a zone 0 to zone XIII. Set exposure for zone VI and expose. Then use a compensating developer to pull the highlights back a zone or two.
The preflash of the film gives some density to the base shadows. Any additional exposure of low shadow values will add some detail to those shadows because the threshold has already been reached with the preflash. The compensating developer then brings the extreme highlights back into printing range.

The film preflash has no effect on mid and high values. Remember that film sensitivity is exponential so a small exposure only affects low values.
So the effect of the preflash is to bend/lift the toe of the characteristic curve up a little in the same way as reducing development bends the shoulder of the curve down.

Works in theory and it can in practise but don't expect good shadow separation if you try it becuase that bending of the curve is flatenning the curve a little at that point in the same way as reducing dev flattens the curve at the shoulder. But it can put some detail into low values that would have been blocked up if you had just exposed for high values.

[edit]
p.s. some people put a diffuser over the lens to do a film preflash so no evely illuminated subject is required.
[/edit]

[Christopher Walrath]

Pick a non-textured, evenly illuminated surface such as a wall and set up your camera before it. Meter the surface and record the reading. Set up your camera to expose, placing this reading on Zone II (reduce exposure by three stops). FOCUS TO INFINITY so as not to record unwanted detail on the neg to interfere with your photograph. Expose the film.

Now you have a negative that will raise your shadows. Zone O adds 0 unit of exposure. Zone I prvides 1 units. Zone II provides 2 units. Zone III provides 4 units. Zone IV provides 8. Zone V provides 16. Zone VI provides 32. And so on.

If you expose as mentioned above you are giving a Zone II preexposure. This adds 2 units of exposure to all exposure zones. So you raise anything that would normally be placed on Zone O from 0 to 2 untis of exposure, effectively raising Zone O components up to Zone II (2 units). Anything on Zone I (1+2=3) raises to between Zones II and III (2 and 4 respectively). Anything on Zone II (2 units) raises to Zone III (2+2=4). Anything on Zone III (4 units) raises to slightly more than halfway (5.6 units) between Zones III and IV (4+2=6). Above this the change is not really noticeable.

You can preexpose for a Zone I setting or a Zone III setting. Even a Zone VI setting. Whatever you decide 'cause it's your negative.

This requires practice to know what it is going to do to your negatives. However once mastered it's just one more tool at your disposal.