Tanning developers and zone system calibration
This might sound dumb, but can I calibrate zone system for tanning developer (for example Pyrocat-HD) using densitometer like I do with non-tanning developers?
I am bit concerned about effect of tanning on highlights.
What sort of densitometer do you use or have access to? One with UV capability is best but blue channel will get you usable results, too. I think that when you get accustomed to using PyroCat HD, you will find that the highlights will not present a struggle to control and somewhat seem to take care of themselves. You might look at the articles area of Unblinkingeye for some good info related to this:
Most developers are tanning developers to one degree or another. Perhaps you are thinking of staining developers, which your example certainly is. The calibration of staining developers for Zone System use depends on the type of printing you will do, as different printing materials may see different contrast in the same negative. If your densitometer can be made, by proper filtration, to see the negative as does the printing material, then you can certainly do the calibration with the densitometer, but you must also then calibrate your printing material. In order to do that properly, you must know more about the color and relative silver and stain density than most of us do. Perhaps it would be more useful to use the printing material itself as the densitometer by simply printing the sensitometric film test strip on it and seeing which steps produce the Zone III and Zone VIII gray values.
Oh yes, I meant staining developer :rolleyes: and catechin based developers.
I use VC paper, so I guess that I should use blue filtration in densitometer.
I can also do calibration using more empirical manner by printing test negatives but I like also get charasteric curve, that's why densitometer is in my mind.
CATECHIN is capable of both staining and tanning development. Sodium sulfite in sufficient quantity will supress the stain.
Originally Posted by Usagi
All of the versions of Pyrocat stain and tan the emulsion proportional to the amount of exposure. I use the blue channel on my color densitometer to measure the stain density produced by Pyrocat.
Tanning may affect the highlights somewhat by facilitating compensating development.
In any case, all of the Pyrocat variants are excellent at holding highlight detail.
Last edited by Tom Hoskinson; 09-12-2007 at 09:54 AM. Click to view previous post history.
Everything is analog - even digital :D
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Unless you are viewing the film image directly, its characteristic curve tells you little about how the same negative will print on various materials. You can forego the various filters you might have to use on your densitometer by using a reflection densitometer and reading the curve of the prints. This is my opinion, of course, which may seem strange because my whole employment history has been as an aerospace engineer, who should by rights be enamored of measuring devices and equations. Remember, however, the famous bridge that fell because of wind-induced oscillations. Measurements and calculations are only worth as much as the accuracy of their predictions, which in turn are only worth as much as the theories at their base.
Originally Posted by Usagi
You can use a stoufer step wedge to figure out curves. Contact print it with a stained negative with steps on it. You can read the density of the stepwedge with your densitometer as normal, and you can compare the prints to find a similar tone. Read the stained negative with your denisitometer. Figure out the adjustment function for the readings. There you go. Usually, very low density readings, say about .1 above film base plus fog will read the same, as the stain is a greater percentage the more density you get.
I think one of the goals is trying to compare the characteristic curve of one film and developer combination with another. This is easier when the intent is to print on graded paper. It becomes more complicated when the intent is to print on variable contrast paper as there will be a different result depending on what filtration is used. With staining developers, this becomes even more complicated with variable contrast paper as the proportional stain effects the contrast to a greater degree in the denser parts of the negative than it does in the lighter part of the negative. I think it would be very interesting if someone could take prints of negatives developed with a staining developer and reverse calculate the "effective" characteristic curve in a way that would allow a meaningful comparison with other films and developers and to really quantify the effect of the proportional stain with the highlights.
I'm new to staining developers too, and have been wondering about this question. My densitometer reads both UV and blue channel, and I'm not sure which channel will give the most accurate readings for negatives to be printed on graded paper.
Originally Posted by craigclu
I read somewhere (maybe Sandy?) that you should use the UV readings for alternative processes, and the blue channel for graded paper, but I'm not sure.
My understanding is that it also depends on if the stain is caused by Pyrocatechin or Pyrogallol, because the color of the stains are different.
Any clarification would be greatly appreciated!
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I calibrated ZS using empirical test method (by printing test strips in the darkroom). So I got minimum exposure time for getting pure black from base+fog, I got zone I and zone IX at their places.
That's purely true ofcourse only on my equipments.
Now I have thought, that can I read densities from these calibrated negatives using blue channel and calibrate another staining+tanning developer using these densities?
For example, if I read density from calibrated stained negative of zone VIII and calibrate another film so that it's VIII has about same density?
Does this approach sound reasonable?