Well, the slope of the curve determines overall negative contrast, the toe determines film speed / shadow detail, and the shoulder (and its slope) determines highlight contrast and density.
The most important thing for the mid-tones is to make sure you have enough exposure in your negative to well define all those tones that you find important. Then develop the film so that they print the way you want them to. Keep in mind that different papers (and paper developers) exhibit different tonality too, so it's best to keep those constant.
My own method is to target Grade 2 to Grade 3, printing on Ilford MGIV matte fiber using replenished Ethol LPD. That requires a negative of high contrast in order to make the blacks convincing without making the rest of the tone spectrum muddy and flat. I don't have equipment to measure any of it, just a method that I work with to get what I want. I always target the paper with everything that I do. That's where it all begins.
Over-exposed negatives print with midtones too light (if you use your darkroom skills to print darks and highlights correct). Likewise underexposed negatives print with the midtones too dark (if you use your darkroom skills to print the darks and highlights correct). As Thomas points out, variations in negative development don't have much to do with it.
I get better results if I avoid negatives of such high contrast that they require a very low contrast setting on VC paper. It might have something to do with the comments on "pathologic condition" in this article:
Of course, it depends on the look you want and your enlarger's characteristics.
A lower gradient doesn't imply more mid-tone detail.
Originally Posted by veedub472
If you're thinking about it in terms of curves, start with some basic sensitometry. It will help you get an understanding of film and paper characteristic curves, and the relationships between them. The path from exposure to film processing to print tonality is called tone reproduction. Both Kodak and Ilford have helpful primer publications on sensitometry and variable contrast printing.
If one carries through a peg point from scene to paper, say a mid-tone instead of a highlight or shadow, then the mid-tones will typically print essentially the same, not too light, not too dark. This assumes development remains constant and that the mid-tones remains somewhere on the straight line. In this case the highlight and shadow detail will change around the mid-tone peg (moving lighter or darker as they fall off the film curve) and the mid-tones will print normally.
Originally Posted by ic-racer
I'm struggling to explain myself properly with this.
I guess all I was trying to say is that if I've developed the film for too long then information that should've fallen at a mid-tone value may have been shifted up in density value as the curve became steeper/gamma or contrast index increased - In the end I have lost mid-tone detail. The lower gradient that should have been produced by correct development contains the ability to capture a wider spread of exposure values in the mid-tones.
When I develop Delta 400 too far I get the same effect - I always stop short of the recommended times now.
My roll of film has a variety of under and over exposed frames - I bracketed quite a few by a stop either way. All frames require a grade 0 or grade 1/2 filter to print the mid-tones (either dark when under-exposed or light when over-exposed), and after reading the attachment about variable contrast paper in john_s's reply I'd really like to get back up to grade 2 or thereabouts.
I work a lot with response curves digitally (both in photography for exposure and in audio for dynamic compression) and don't disagree with anything I've read in the replies so far - but due to unclear communication seem to have dug a hole for myself!!
Thanks for your patience.
Adjusting the development of the film (+ or -), changes the relationship to the paper, how much info from the negative prints. You do not loose detail on the negative.
Originally Posted by veedub472
To print the mid tone detail you may need to adjust your printing process. Say change your peg, or burn and dodge, or ...
How are you pegging exposure for the print?
One of the most helpful things for this sort of question is to take a sample strip of negs in your left hand, a digisnaps camera in your right hand, hold the negs so they are lit from behind (by a window + sky for example) and make a focussed picture. Then people can comment on what your negs look like in comparison to theirs, and discuss actions to change the results. Secondly, make sure your paper isn't ancient and/or cooked, as that can have unfortunate results on what can be printed successfully!
Forget everything you know from your adventures digitally and with sound, and start with a blank sheet. Don't even worry about curves.
Originally Posted by veedub472
- Is your paper fresh? If not, acquire fresh paper.
- Is your paper developing chemistry fresh? If not, acquire fresh developer.
- As mentioned earlier, your paper and paper developer have a certain range that it's capable of, and how the print looks is a relationship between the paper/developer/print developing time, and what you do to expose and develop your negative.
- So, do a film exposure test, where you meter normally and shoot a typical static scene, but you bracket your exposures, say at EI 12, 25, and 50. Then develop it 'normal'.
- Now print all three brackets at Grade 2, to a point where you have good black (meaning shadows that appeal to you, how you like them to look). Do NOT worry about highlights at this point.
- Pick the exposure index you liked, say EI 25, and shoot an entire roll at that speed, metering normally, a static scene that is preferably the same as what you shot in the first part, in similar light.
- Now develop one third of this roll at a time, and print one of the negs. At 'normal' film dev time, do your highlights look like they have enough detail, or too much, or are they perfect? If the negative is too dense in the highlights and you can't get enough detail in the highlights, you need to shorten film development time, say 20%. If the highlights are dull and gray without beautiful variations of almost white, you need to increase film development time, about 20%. Now print the negs again.
- Continue doing this adjustment of film developing time until your negatives print with satisfying blacks and whites, and your mid-tones will be beautiful by default.
This really is the only way to get a feel for how you need to expose and develop your negatives so that they print well. Keep paper and chemistry fresh. Do not change paper or chemistry types at any time during this test, and do not be tempted to change from contrast grade 2. Keep all other things equal. The only thing that changes is how you expose and process film, and your paper enlarger exposure time will also change due to changing negative densities.
When you learn how to treat 'normal contrast and lighting' you will discover that low contrast scenes and high contrast scenes may require different treatment. You will also discover that no matter how consistent you try to be with film exposure and development, different negatives on the same roll of film will require changes in how you print them, and it's at this point you break out the other contrast grades, to compensate for these naturally occurring differences (or, if you simply want more or less contrast out of a scene than you had originally envisioned). It's good to get tuned into a mid grade as your 'target' or 'peg' (as Mark calls it), because then you have a lot of 'wiggle room' at the time of printing. If you're already at an extreme grade, like 0 or 5, if you need 'more' you are making it very difficult for yourself.
Just forget about curves, and go find out how to make your negative fit the qualities of the paper. That is all that really matters.
Thanks for taking the time to put your last post together, it's much appreciated and I'll be giving it a go as soon as I get some more supplies.
I've always made prints in the past between grades 1.5 and 2.5 from straight 400 and pushed 400 with little trouble, although, I doubt I'm getting the best results without undertaking the process you have described.
So thanks again and to all who've taken the time to reply.