Exposure curves for alternative processes
One gang of people like to produce digital negatives as intermediates in alternative processes. They then obsess about the UV blocking power of the inks for different processes and bang on about log D values for each different process.
All of which is a long way of saying that despite an expensive physics and chemistry education I have some mental blank about curves and thus have problems every time I walk up to PhotoShop. I make my 8x10 negatives in a dev tray but the above kinds of discussion make me wonder about whether I should be exposing differently, developing differently for different AP's.
1) wanted a boy's and girl's first book of densitometry
2) experience of messing with exposing/developing for different AP -- I'd like to start with salt print
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Originally Posted by aldobranti
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With regards to your 8x10 film negatives, I think you have to ask yourself this question:
Is this negative intended for a single process, or do I wish to make prints from several different processes?
For example a silver-gelatin print, a platinum print, and a carbon print will require negatives with different density ranges. A negative that prints really well as a carbon print will likely be too contrasty to print on silver gelatin, even with a very soft (0) filter.
In my opinion, if you plan on making silver prints as well, it's probably best to develop for silver printing, and then make dupe negatives, using either a reversal process with litho film, or directly with x-ray duping film, and adjust the density range of these dupes through exposure and development techniques. This applies to 8x10 original negatives as well smaller formats for which you make enlarged duplicate negatives for alt-process. You'll need to make less aggressive contrast adjustments (if any) in your alt-process chemistry, which is probably a good thing.
I make my alt negatives by digital methods, but if I were using film, this is the approach I would take, and I would likely optimize a dupe negative for a specific process. You can always make another dupe relatively easily for a different process.
A 21-step step wedge is your friend in alt-process. You can make a print of it to determine the density requirements of your process and method, and then use it as a visual guide for judging your negatives, if you don't have access to a densitometer.
Hope that helps.
I second the step wedge advice.
I print a 1/2x5" one on the margin of every alt process print I make as a sort of QC check, even after I have figured out the contrast needs of the process and the negative contrast to match to it.
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I usually determine which process I will be printing with before I set up the camera, or if I am not sure, expose at least two negatives so that I can fool with the development. I find that the exposure is usually the same and it is just the development that changes with the intended process (either pt/pd or carbon -- with more development for carbon).
One of the reasons I decide which process early is that I use the single-transfer carbon method which reverses the image, and that needs to be taken into consideration when composing.
At least with LF landscape, a bad day of photography can still be a good day of exercise.
As i understand your original message, you are currently interested primarily interested in producing salt prints from your in -camera negatives. I have been making such prints for several years and have made them from every conceivable type of negative including a paper negative from the 1840's. in an attempt to help you achieve at least a modicum of success right away I offer the following. A densitometer is not necessary, but good visual observation will help fine tune your process.
1. I use only Ilford FP4+ because it is the best current film for building contrast.
2. I expose it at an EI of 100 in order to have very thin shadow density.
3. My development times have been carefully calculated for the developers I use. I suggest that you start with your current developer of choice. HC 110 dilution "A" is a good choice. If you happen to be using this developer ow at Dilution"B", just use "A" at your current times for "B"
4. Double you normal development times if you are using other developers.
Your goal is a negative with shadow detail barely visible, and Highlights through which it is difficult to read a newspaper in normal reading light.
These methods will get you in the ball park and you will need to fine tune them for optimal prints. In the prints you are looking for open shadows and good white highlights.
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Reeder and Hinkel describe a fairly easy process for producing curves for any process, equipment, and paper in their book "Digital Negatives." It uses standard Photoshop tools and is self compensating for different printers and materials. Burkholder also describes the process, in a somewhat more complicated way, in his "Making Digital Negatives for Contact Printing." He also gives some quite usable curves for popular processes.
Basically, you first make a test strip through your negative material to determine the exposure needed for D-Max. Then you print a step tablet on your negative material and print it using the exposure you determined. Then you measure the densities of the steps on the print and derive the curve.