Edge efects with Pyrocat-HD

[Dave Krueger]

1. Because as you add magenta you progressively reduce the impact of the stain, since the green part of the emulsion is less and less in play. This reduces or eliminate shouldering, but the rest of the curve is not affected.

2. It is not that all green light is blocked by a #3.5 filter, but that as you increase the amount of magenta more and more, more green light is blocked. At 3.5 a very great percentage of the green light is blocked, but you have to go all the way to the highest number to block close to 100%. However, at 3.5 the blocking is already so great that the yellow/greeen/brown stain of the negative is no longer in play, I as mention above.

I have run curves on this and when you get to filter #3.5 with VC papers the curve is virtually identical to what you would see with a graded paper that has only sensitivity to blue light. That is, there is no shoulder compression that can be contributed to stain.

Sandy King

I went back and re-examined my HD vs MC test prints. The MC print required higher contrast filtration to get essentially the same contrast, but that could probably be adjusted with development time. The interesting thing is that I no longer see the compression in the highlights that I was so sure I had seen previously. The entire MC print was lower contrast until I increased the contrast filter from 25M to 50M. The HD print only needed 25M.

But I noticed something else even more interesting. In another thread you posted that the edge effects are greater with MC than HD. That's what made me go look at these prints again. I don't see these edge effects in any of my prints when I look at an individual light gray to dark edge. But when I look at an area with lots of fine detail, it's apparent as higher contrast. And even more astonishing (to me) is the fact that the low contrast MC print (printed with a 25M filter) shows significantly HIGHER contrast than the higher contrast HD print in the bushes and grass.

You guys who have trained eyes probably notice this stuff without giving it a second thought, but I feel like I've made a new discovery. MC has now been reinstated into my developer competition.

I noticed that my Pyrocat MC Part A (in glycol) has turned amber. Is that ok? I think I've used it like that in the past with no problem, but just curious. Hell, maybe it's always been amber. I don't even remember.

 

[sanking]

I went back and re-examined my HD vs MC test prints. The MC print required higher contrast filtration to get essentially the same contrast, but that could probably be adjusted with development time. The interesting thing is that I no longer see the compression in the highlights that I was so sure I had seen previously. The entire MC print was lower contrast until I increased the contrast filter from 25M to 50M. The HD print only needed 25M.

But I noticed something else even more interesting. In another thread you posted that the edge effects are greater with MC than HD. That's what made me go look at these prints again. I don't see these edge effects in any of my prints when I look at an individual light gray to dark edge. But when I look at an area with lots of fine detail, it's apparent as higher contrast. And even more astonishing (to me) is the fact that the low contrast MC print (printed with a 25M filter) shows significantly HIGHER contrast than the higher contrast HD print in the bushes and grass.

You guys who have trained eyes probably notice this stuff without giving it a second thought, but I feel like I've made a new discovery. MC has now been reinstated into my developer competition.

I noticed that my Pyrocat MC Part A (in glycol) has turned amber. Is that ok? I think I've used it like that in the past with no problem, but just curious. Hell, maybe it's always been amber. I don't even remember.

Hi Dave,

Congratulations on what you have learned from the experiments and from looking. It is always gratifying when we discover things for ourselves.

About the color, the color of the Pyrocat-MC in glycol does appear to darken with age. The oldest I have is now about 7-8 months old and is dark amber in color, compared to very light amber when first mixed. But I don't know why the color change, but it still works fine. By contrast, I notice that the Pyrocat-HD in glycol does not darken with age, or if so, it darkens much less than -MC.

Sandy King

 

[gainer]

When you mix the metol withe the small amount of TEA and water, you get some kind of TEA-sulfite I expect. I don't know if that has anything to do with the color changing over time. I have some rather old PC-TEA that is quite dark but still very active. I use it these days diluted about 1+31 as rint developer.

We all know how much Rodinal can change color and still be good. We also know how little XTOL can change color and be bad. When in doubt I use a snip test for 2 minutes. My eyes have gotten pretty well calibrated,

I see less change in Pyrocat PC where I used p-aminophenol in place of the metol, and did not use any TEA. The catechol, p-aminophenol and ascorbic acid all dissolve in glycol. The change in pH due to using ascorbic acid without the TEA is very small by the time the stock is diluted 100:1 and is swamped out by the K2CO3.

 

[Kirk Keyes]

Originally Posted by Dave Krueger
That still doesn't answer my two questions.

1. How is adding magenta or blue is going to reduce just the highlight compression without increasing the contrast over the rest of the tonal scale? Sure, I might eliminate the highlight compression, but at a cost of having objectionably high contrast in the other tones.

1. Because as you add magenta you progressively reduce the impact of the stain, since the green part of the emulsion is less and less in play. This reduces or eliminate shouldering, but the rest of the curve is not affected.

[...]

I have run curves on this and when you get to filter #3.5 with VC papers the curve is virtually identical to what you would see with a graded paper that has only sensitivity to blue light. That is, there is no shoulder compression that can be contributed to stain.

Sandy King

Sandy -

There is a continuum of highlight compression from maximum compression that is acheived by printing with no filtration to no compression that is observed when the magenta filtration diminishes the amount of green light reaching the VC paper. It is not as if the effect simply turns off when the magenta filtration reaches the equivalent of Grade 3.5 (from your example). It must decrease continuosly as the magenta filtration is increase, up to the point that the filtration overwhelms the sensitivity of the green emulsions in the VC paper.

My measurements of old style Ilford MG filters (pre 1990) show that my Saunders 4500 color head gives about 50M to reach the equivalent of Grade 3.5 (that's after subtracting out the magenta that was added in to speed match the filter set). No filtration (0M and 0Y) on that enlarger gives about 2 1/4 grade. So adding 50M ends up being equivalent to about a 1 1/4 grade increase in contrast.

I think Dave is on the right track here when he asks if this "eliminate the highlight compression, but at a cost of having objectionably high contrast in the other tones". I also suggest that it is not possible to cancel out the highlight comression without adding an increase in shadow contrast. It seems that if we increased the grade of the paper that we printed on by adding 50M to the light source (an effective grade increase of 2.25 to 3.5), that we must have increased the contrast of the shadows by a similar amount.

Now it may not be very obvious as the stain is constantly increasing in density as the neg density increases, so that when we have added 50M, the darkest shadows may see an increase in contrast of 1.25 grade, but the middle tones will see a smaller increase in contrast, probably around half as much.

It would be interesting to see a set of tone reproduction curves done with a neg that has 0 filtration added, one with 25M, and one with 50M. It should reflect the increase in conrast in the shadows as the highlight compensation is eliminated.

I guess the question for Dave is if an increase of about 1.25 grades in the deepest shadows is objectionable. I can see where there are times that one would want to increase the tonal separation in the lowest tones without increasing the contrast in the higher tones.

Kirk

 

[sanking]

Kirk,

I understand that there is a continuum of compression and that it is not an onn/off situation. But there is a cross-over between Filter #3 and #4 at which point most of the green light is blocked. That happened to be at about 3.5 with the Ilford multicontrast fiber paper. It would probably be different for most other papers.

In any event, my goal is not to eliminate highlight compensation since I believe that it is useful in the majority of lighting conditions. I merely mentioned this so that people using staining developers would understanad that the use of a VC filter over about 3.5, or dialing in magenta to over about 60 units, effectively eliminates all highlight compensation because it takes the low contrast greeen layer out of the equation, or mostly out of the equation.

In fact, what I suggest is that when using a staining developer with VC papers you should develop to a fairly high CI, much higher than would be appropriate for graded silver papers, and then control contrast with yellow filtration. That way you retain the potential for highlight compensation. If for some reason you want a staining developer that does not have highlight compensation you should develop to a lower CI and increase contrast with magenta filtration.

Not having actually tested the premise I don't know if eliminating the highlight comression will add an increase in shadow contrast. But if that is the case, we can adjust development to a lower CI.

Sandy