Flat Tri-x

Another exposure-related topic mentioned in the OP regards low contrast scenes. Specifically when one meters and exposes based on readings from a conventional reflected meter, the lowest value of the scene will wind up greater than 0.1 log d on the film. It does not have to be that dense to make a good print, and in fact, one can under-expose until the lowest value is 0.1. One way to do this is to use zone system exposure and a spot meter where you can specifically 'place' the low value of the scene.

ic-racer said:

Actually, the specified ISO exposure puts the shadows on the toe. With modern t-grain film you frequently have the option of moving the scene values up the curve (additional exposure). This has the effect of increasing the overall contrast on the negative as DL posted, because the values you intend to print all now fall on the straight portion which has more 'rise' than 'run' compared to the toe.

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This is true, and I confess I neglected to take this into account in my previous post. Exposure can affect contrast, but you have to compare an exposure that ideally captures all of the tones in the scene, to an exposure that doesn't. This could be on the toe or on the shoulder, and therefore may be considered just shadow- or highlight-contrast since it's limited to only a portion of the negative tonality.

The existing light of the scene is like this block of density that is slid up and down the film curve by means of exposure. And the slope of it is changed with development, to some extent with agitation and developer dilution, and we are now changing the entire tone curve in one swoop, meaning total contrast.

I think it's important to separate the two for clarity.

ic-racer said:

Actually, the specified ISO exposure puts the shadows on the toe. With modern t-grain film you frequently have the option of moving the scene values up the curve (additional exposure). This has the effect of increasing the overall contrast on the negative as DL posted, because the values you intend to print all now fall on the straight portion which has more 'rise' than 'run' compared to the toe.

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Two thoughts.

1) Box speed doesn't necessarily put my important detail on the toe, even though it may yours. Your EI and mine, your subject matter and mine, your style and mine: probably don't match; that's okay.

2) If everything I intended to print is on the straight line to start with at box speed then extra exposure doesn't change the contrast, just the placement, it doesn't change my prints. As a practical matter, 1-under or 2-over, meh; it doesn't change my print.

markbarendt said:

The curve (which defines the contrast rate of the film) can only be changed by development differences.

Once one gets an exposure that gets all their important subject matter somewhere between toe and shoulder of the film, the exact placement doesn't change contrast at all.

If one gets an improvement in contrast because of a change in exposure it is because one was exposing poorly in the first place.

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Mark:

Perhaps I was not explicit enough.

When density leaves the toe and all density thus becomes a component of ONLY the straight line portion of the curve, we then have maximum contrast for a given development time. That positioning on only the straight line portion guarantees that there will be more overall contrast (with a limited contrast scene) than when density is positioned on BOTH the toe and straight line, (because the toe portion provides little tonal separation).

NB: I say 'limited contrast scene' because if density starts emerging onto the shoulder, we have, again, a compacting of tonal separation. - David Lyga

David Lyga said:

Mark:

Perhaps I was not explicit enough.

When density leaves the toe and all density thus becomes a component of ONLY the straight line portion of the curve, we then have maximum contrast for a given development time. That positioning on only the straight line portion guarantees that there will be more overall contrast (with a limited contrast scene) than when density is positioned on BOTH the toe and straight line, (because the toe portion provides little tonal separation).

NB: I say 'limited contrast scene' because if density starts emerging onto the shoulder, we have, again, a compacting of tonal separation. - David Lyga

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Were on the same page