Ilford FP4+ Characteristic Curve

[DREW WILEY]

Thank you. I'm often out at Pt Reyes, Mt Tam etc summer about once at week, at least when I'm not in the high country somewhere.

 

[Bill Burk]

I get that. I did it the way I did it because it’s easier in google spreadsheets. My options are to generate the ISO reference the way it is now, generate the way it is now, but with no dots, and generate it with no dots and after the graph image is generated, pull it into photoshop and manually put a dot on 1.0 for the meter point, and 1.3 for the aim point. What’s the preference?

For the horizontal scale along the bottom, converting it to arbitrary relative log units isn’t really that big of a deal, though I’d have to come up with a scale for log meter candle seconds. Is there a reference for this somewhere?

Easiest would be to do a little math on your numbers to “put them where they should be” keep the units and scales you have they are fine. I struggle with how to represent Zone System. For this I took Ansel Adams guidelines for Zone V and Zone VIII highlighted in green. See how nicely you hit N? Starting with your numbers I interpolated 0.1 and assume it shifted 0.05 towards less speed due to lesser than ISO development. I locked the 0.1 point and put all your data points correspondingly. I found the interpolated 0.1 at 0.106 and you can see the math lower right corner. I just added 0.11 (rounded) to each Zone data point to put them where they should be.

 

[Bill Burk]

Again my bottom Log E scale is arbitrary and literally is the density of a step wedge on my sensitometer which arbitrarily puts about 0.3 log meter candle seconds at the film plane. You absolutely can change that to be 0 anywhere you like, for example the speed point, Zone V or the metered point if you like. Towards left is less light, towards right is more light. (My scale goes up from right to left only because it’s “attenuation”).

I picked Ansel Adams’ Zone V and Zone VIII ranges for diffusion enlarger.

 

[Adrian Bacon]

Again my bottom Log E scale is arbitrary and literally is the density of a step wedge on my sensitometer which arbitrarily puts about 0.3 log meter candle seconds at the film plane. You absolutely can change that to be 0 anywhere you like, for example the speed point, Zone V or the metered point if you like. Towards left is less light, towards right is more light. (My scale goes up from right to left only because it’s “attenuation”).

I picked Ansel Adams’ Zone V and Zone VIII ranges for diffusion enlarger.

I think I'll keep it log units, but put the zero at the far left so left to right is more exposure, as that logically makes sense.

For your last chart you posted, I've looked at it, but I need to noodle on it a bit, particularly the interpolating zone 1 part. I think my last chart is pretty close, but I didn't do the zone 1 interpolation part, so I'll see if I can work that in and post the results.

Thank you for this input and your time. This has been pretty instructive.

 

[Bill Burk]

Thanks, This has been fun for me too. I don't think anyone's done a graph showing the relationships of ISO and Zone System in this way, and I think it's a good way to show the differences. (I like what this is beginning to reveal).

Actually, if you use the scale 0.0 on the right -3.0 on the left, that is like your last graph, that is a good fairly common way to do it. Log meter candle seconds... negative log values just mean smaller numbers. 0.0 is one, -1.0 is 1/10th, -2.0 is 1/100th, down to -3.0 is 1/1000th of the light at the far left (less light as you go to the left).

Interpolating is really easy and self-confirming. (The correct answer looks right on the graph, incorrect math doesn't even come close).

I like the way Zone V at EI 64 can get you 0.7 density... and Metered point by ISO 125 can get you 0.72 density... and everyone assumes they are the same. But notice how with Zone System you downrate the film by nearly 1 stop, and that would lead to higher density except with Zone System you develop to a lower contrast, and that leads to a lower density - the two practically cancel out.

In practice, don't plan on developing to ISO, that's just for testing. After you find the test times for ISO to confirm your process conditions, you dial down the contrast slightly.

 

[Adrian Bacon]

Thanks, This has been fun for me too. I don't think anyone's done a graph showing the relationships of ISO and Zone System in this way, and I think it's a good way to show the differences. (I like what this is beginning to reveal).

Well, it's just me trying to wrap my own brain around how this works and how the two are related. My original graph was actually an accident as I was just trying to make sense of the two systems and come up with a reasonable way to determine rough development time and approximate speed with the equipment I had available to me. I knew I was on to something when I did a couple of exposure and development iterations and saw what was happening on the graph, though I feel sharing here on photrio has led to quite a bit of refinement in that.

 

[Adrian Bacon]

Easiest would be to do a little math on your numbers to “put them where they should be” keep the units and scales you have they are fine. I struggle with how to represent Zone System. For this I took Ansel Adams guidelines for Zone V and Zone VIII highlighted in green. See how nicely you hit N? Starting with your numbers I interpolated 0.1 and assume it shifted 0.05 towards less speed due to lesser than ISO development. I locked the 0.1 point and put all your data points correspondingly. I found the interpolated 0.1 at 0.106 and you can see the math lower right corner. I just added 0.11 (rounded) to each Zone data point to put them where they should be.

Just to make sure I'm getting this right... on your graph, points 2.65 is reference zone 0, 2.35 is reference zone 1, 2.05 is reference zone 2 correct? point 2.46 is my 4 stops down 0.128 sample data correct? So the zone reference data is offset by the interpolated zone 1 value in exposure units along the horizontal scale? Correct?

 

[Adrian Bacon]

Just to make sure I'm getting this right... on your graph, points 2.65 is reference zone 0, 2.35 is reference zone 1, 2.05 is reference zone 2 correct? point 2.46 is my 4 stops down 0.128 sample data correct? So the zone reference data is offset by the interpolated zone 1 value in exposure units along the horizontal scale? Correct?

Nevermind. I figured that part out. The 0.11 is the offset from the 0.05 mark for my data. I put the zone 1 reference data starting at 0.05. See attached chart. If that's not correct and should still be at the same place as the ISO speed point, then say so.

 

[ic-racer]

Except for Zone I, Zone system negative densities are pretty specific to a given worker's exposure, development and printing protocol. Like the weight of your camera bag. A little useful to share, out of curiosity. Like if you camera bag weights 50 Kg or 50 grams you are probably doing something wrong.

 

[Adrian Bacon]

Except for Zone I, Zone system negative densities are pretty specific to a given worker's exposure, development and printing protocol

It’s only that way if you choose for it to be that way. If that’s what people prefer, then that’s up to them, however in my experience, even a small amount of applied rigor produces remarkably consistent results from one worker to the next. Yes, there will be variations, but in actuality, they’ll be relatively small as long as a given protocol is reasonably followed.

 

[Bill Burk]

2.46 is Zone I according to my best guess. The zones all shift 0.11 to the left. They shift because you didn’t have a sample point at 0.1 (it’s not necessary or even desirable to have a sample hit 0.1).

Your latest graph is nice. Zone and film look good. The ISO is too steep. Metered point should be at density 0.72 and 1.21 should be at 0.9

 

[Bill Burk]

Except for Zone I, Zone system negative densities are pretty specific to a given worker's exposure, development and printing protocol. Like the weight of your camera bag. A little useful to share, out of curiosity. Like if you camera bag weights 50 Kg or 50 grams you are probably doing something wrong.

Ansel Adams (reluctantly I think) gave a few suggested densities for N and since they target Grade 2 diffusion enlargers they are a satisfactory starting point.

 

[Bill Burk]

p.s your Log E exposure scale looks great. I don’t even think you have to disclaim it “relative” log exposure since the value scale is absolute. I like it that way. But check a few manufacturers graphs. They might go from 0 on the left to 3 on the right so that amateurs aren’t confused - then they call it “relative”.

 

[Bill Burk]

And one further point. ISO and EI.

Film would be ISO 125. Many workers would call it EI 100 (standard metering technique at this development) and Zone System workers would call it EI 80 (Zone System metering technique.) 7 minutes is N.

But I also refer to Delta-X and I do not make the nitpicking shift from ISO 125 to EI 100 when the speed point moves with development. That came from BTZS and I don’t implement that.

I do set my camera at EI 125 and my spotmeter at EI 80 for Zone System metering technique. So if you agree wit me that can be a helpful label for all your graphs. ISO and 2/3 stop less go Zone System metering technique.

When you start to use different developers that don’t give full speed, or aging film, then the main speed would be whatever you find. Otherwise you should find ISO

 

[Adrian Bacon]

p.s your Log E exposure scale looks great. I don’t even think you have to disclaim it “relative” log exposure since the value scale is absolute. I like it that way. But check a few manufacturers graphs. They might go from 0 on the left to 3 on the right so that amateurs aren’t confused - then they call it “relative”.

Funny you should mention that as I was just looking at Kodak’s to see what they did.

RE ISO scale, good catch. It was late. I gotta get going on my day, so it’ll be later when I have some time.

 

[Adrian Bacon]

And one further point. ISO and EI.

Film would be ISO 125. Many workers would call it EI 100 (standard metering technique at this development) and Zone System workers would call it EI 80 (Zone System metering technique.) 7 minutes is N.

But I also refer to Delta-X and I do not make the nitpicking shift from ISO 125 to EI 100 when the speed point moves with development. That came from BTZS and I don’t implement that.

I do set my camera at EI 125 and my spotmeter at EI 80 for Zone System metering technique. So if you agree wit me that can be a helpful label for all your graphs. ISO and 2/3 stop less go Zone System metering technique.

When you start to use different developers that don’t give full speed, or aging film, then the main speed would be whatever you find. Otherwise you should find ISO

I don’t have any disagreements, but would have to look to see if I can apply labels like that in google spreadsheets.

 

[Bill Burk]

I don’t have any disagreements, but would have to look to see if I can apply labels like that in google spreadsheets.

You could just say at the top: ISO 125 (EI 80 for Zone System)

 

[Adrian Bacon]

You could just say at the top: ISO 125 (EI 80 for Zone System)

Alright. Here is the latest version. If there are no further changes to make, I'll update the original post so people don't have to scroll all the way to the bottom to get the best one. If there is anything else to change, say it now or forever hold your peace . I've got a whole stack of sample data from other emulsions to do this on.

 

[Bill Burk]

Perfect!

 

[Adrian Bacon]

apparently you can only edit the last post you made. I can't seem to figure out how to update a previous post. bummer. well at least there's a good chart posted.

 

[MattKing]

apparently you can only edit the last post you made. I can't seem to figure out how to update a previous post. bummer. well at least there's a good chart posted.

A moderator could do an edit for you - "report" the post that you wish edited, and ask.
If you were in the MSA sub-forum, I could use my mini-moderator powers and do it for you .
It might help if you posted a new post which is exactly what you want, and then ask the moderator to delete the older, earlier post.

 

[Adrian Bacon]

A moderator could do an edit for you - "report" the post that you wish edited, and ask.
If you were in the MSA sub-forum, I could use my mini-moderator powers and do it for you .
It might help if you posted a new post which is exactly what you want, and then ask the moderator to delete the older, earlier post.

I don't know if I want this thread deleted... It has some really useful information. I'll report the original post and ask to have the image updated to the one in post #43

 

[Stephen Benskin]

Can you explain what you mean by "ISO Standard Contrast Curve?" If it's referring to the curve parameters used in the ISO speed standard, then it's not applicable in this case.

Does the ISO standard define what density a correctly exposed grey card should be? I don't recall that it does, as that's a zone system thing, though I might be wrong about that. It happens.

It doesn't work that way. It depends on the film curve. Also, the negative is an intermediate step and the paper curve is an additional influence. Don't get stuck on any target density. It's not about density. It's about contrast.

 

[Adrian Bacon]

Can you explain what you mean by "ISO Standard Contrast Curve?" If it's referring to the curve parameters used in the ISO speed standard, then it's not applicable in this case.



It doesn't work that way. It depends on the film curve. Also, the negative is an intermediate step and the paper curve is an additional influence. Don't get stuck on any target density. It's not about density. It's about contrast.

The curve parameters in the ISO speed standard.

 

[Bill Burk]

Stephen, I had Adrian mark (in red) the ASA parameters for 125 film, plus the ‘10x’ point. Then for Zone System he took Ralph’s (I think) densities for Zone V and Zone VIII. (Close enough to Ansel Adams’ suggestions to work for me). He extrapolated the other Zones. We took the Zone Reference 0.1 speed point and shifted it to the right 0.05 (an arbitrary guess) from ISO 125 speed point to reflect where I think the lesser development for Zone System N may move it.

The result is a red ISO Reference and a green Zone System Reference for N.

Then his characteristic curve is yellow and we put the interpolated 0.1 on the Zone I mark. The yellow dots are his data points.

I think it’s perfect and could only be better if we find the absolute speed point shift due to Zone N development. For now 0.05 is my best guess.