You stated : "with colour negative film....the detail in both the highlights and the shadows fall within the linear part of any given curve"
Any colour negative film, as any film, has limited capacity to reproduce subject brightness differences. If the the brightness range of the subject exceeds that capacity of the film, shadows or highlights or both (depending on exposure) are lost.
In general, films designed and processed to yield a negative have the greatest of such capacity.
so how does this come in the "toe and shoulder" definition I'm after.....basically the 'toe' and 'shoulder' are the limits so to speak????? like Zone 2 and Zone 8 in the zone system which are in effects the limits of detail coming through in highlights and negatives.....
Originally Posted by AgX
Last edited by sperera; 04-05-2010 at 08:38 AM. Click to view previous post history.
I definitely qualify as non-scientific... (I'm the head of the arts dept. at a high school outside Windsor ON.) I will most likely be called out for gross inaccuracies or generalizations, but this is the way I view the concept.
What you are asking is of most value with films that you test and develop yourself. (most often Black and white, but some of the concepts are applicable to colour) Generally speaking, your knowledge of toe and shoulder are mostly used in keeping important shadow or highlight details out of those areas. As your post suggests, any film responds best in the linear portion of the curve. Separation of tones in the toe and shoulder are greatly compressed, and much harder to control, leading to blocked shadows and blown highlights. Within the exposure latitude of your film, you want to place as much of the important detail within the straight line portion of the curve. For a wider range, you can expand or contract your development, N+1, N-1, but that is another discussion.
I think I'll let Bruce tell you. He's much better at it than I am.
Last edited by Toffle; 04-05-2010 at 10:26 AM. Click to view previous post history.
Tom, on Point Pelee, Canada
Ansel Adams had the Zone System... I'm working on the points
system. First I points it here, and then I points it there...
The relationship between negative density and exposure is mathematically linear.
But there are practical limitations to this because the film emulsion has limits to how much density, (shoulder), or how little density, (toe), it can record. If you plot a graph with exposure along one axis and negative density along the other, and you plot the densities of each zone, and then connect the dots you will see a curve which represents how the film reacts to exposure and development.
The curve is S-shaped, and in the middle it's reasonably straight. Different films have more or less of an ability to record a long straight line. A straight line means that you have a normal relationship between negative density and exposure+development. The shoulder is at the top of the curve and represents where the highlight densities start to block up, and are unable to record detail with much separation, i.e. the negative highlights become difficult to print and a lot of dodging and burning becomes necessary to record tone in your print in those areas.
The toe is at the bottom of the curve, and generally means shadow details that are so vague that they either don't exist, or they are not clearly visible due to the density of the film base and any potential existing fog at the very low end of the toe, and right where the tone curve stops being a straight line, separation between shadow values are difficult to record in your print.
So, in summary you want enough exposure (and also long enough development time) to get substantial shadow detail density that print easily, and you will want to develop your negative at an appropriate duration of time and adjust your agitation intervals to keep highlights where they too are printable, i.e. below the shoulder.
Then of course there may be situations where you either can't help breaking the rules, or you might even want to break the rules and expose too little on purpose, or develop your film for much too long, to achieve a certain effect. There is no right or wrong, but it's important to understand these relationships, if you wish to be able to control how your prints will eventually look.
I hope that helps more than confuses things.
Last edited by Thomas Bertilsson; 04-05-2010 at 10:51 AM. Click to view previous post history.
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Toe is where shadows lose contrast and get flat, but not completely blocked.
Shoulder is where highlights lose contrast and get flat, but not completely blown-out.
Last edited by hrst; 04-05-2010 at 10:38 AM. Click to view previous post history.
Toffle, nice assist on the Bruce videoM I always found that clip imensely helpfulM
"There is a time and place for all things, the difficulty is to use them only in their proper time and places." -- Robert Henri
I prefer to call the nonlinear portions the toe and knee; then the part in between can be called the shin... and if you look down at your leg, you see exactly what's going on
Originally Posted by sperera
Note that most discussions of how to control the toe and knee/shoulder are in the context of b&w film. You can manipulate those regions somewhat with the c41 process, but not to the extent that is commonly done with the b&w process. With b&w film, you can get very different exposure-density curves... from the same film. With all the 160 colour neg films, the curves generally look quite similar. If you really want to see a big difference, compare the curves of one of the colour neg films to a slide film.