Adventures in film characteristic analysis

bernard_L · Feb 6, 2022

@ Stephen Benskin. Thank you for taking the time to write these detailed and clear explanations, sharing your knowledge. I'll make sure to read them for the sake of my curiosity and education.

But I believe the weak point in the chain, as far as I'm concerned, is when I stand in front of the scene with my camera and meter; 4-stop difference between average shadow region and average sunlit region; what to do? Play safe and place average shadow on Z.IV? But maybe the highlights will be on the shoulder and lose brilliance, Or place average shadow on Z.III; maybe lose some separation in the deepest shadows? And maybe some of these deep shadows do not need to be separated in the final print, so why worry? Or maybe they do? Please note that the significant quantum in this decision process is whole stops, not 1/3 stops.

Stephen Benskin · Feb 6, 2022

bernard_L said:
I don't see how the vertical scale is distorted. Looks linear to me.
On second looks, I understand that Stephen Benskin's curve (post #110) is a re-draw of radian's data (post #106) for 6 minutes devt; with different offsets on both scales; plus, dots alone without connecting lines masks the implausible hump at 4th point from left, which is most prominent on the 12min curve (orange dots) not re-drawn by Stephen Benskin. I'm still definitely not buying the "12min" curve.
View attachment 297721

I didn't want to do it, but you made me curious. With the original looking curves, it all totally looked a bit hopeless, but after retyping the data and making the log-H relative (didn't try actual. I just wanted to eliminate more variables). It looks more real. Usable or not, the jury is still out. There appears to be two jumps in the data values. Can't really tell whether it's from reading or exposing the strip, but curve smoothing could fix it. There definitely needs to be more in the tow and maybe it overall needs to be more granular. Plot it in 0.15 step intervals.

Bill's plotting paper has more precise markings and he is able to interpret the curves better.

Recommended fix: use a single light source and contact a step tablet, then it's possible to have a curve that can be confidently interpreted and applied to photographic use.

bernard_L · Feb 6, 2022

Stephen Benskin said:
I didn't want to do it, but you made me curious.

Sorry, that was not the intent

Stephen Benskin said:
but curve smoothing could fix it

Disagree strongly. Fixing a problem by data massaging can be justified only if the cause of the problem has been identified and the numerical fix addresses the problem one-to-one. Other than that, it's just sweeping under the rug.
For instance, one possible (just for the sake of the argument) cause for the curve "hump" would be one missing step in the sequence of illumoinations. No amount of curve smoothing is going to properly address this.

Stephen Benskin said:
Recommended fix: use a single light source and contact a step tablet

Agree Re: step tablet, but achieving uniform illumination is not trivial.

Anon Ymous · Feb 6, 2022

bernard_L said:
... Agree Re: step tablet, but achieving uniform illumination is not trivial.

Perhaps a strong enough light source, far enough to be uniform and with some diffusion material in between? An array of leds?

Adrian Bacon · Feb 6, 2022

radiant said:
One thing that is horribly wrong is the exposure amount. There are only maybe two-three stops visible under the 18% gray - position. Andrian Bacon writes " If you expose the film at EI 400 or 500 you will get very usable images with a solid 4-5 stops of shadow detail below a correctly exposed 18 percent grey card before film base plus fog and 5+ stops of highlight density with an easy 2-3 stops of over exposure latitude if you need it, though, you don’t really need to give it that much exposure." here https://adrianbacon.com/simple-photography-services/simple-film-lab/films/400hp5/

So maybe my exposure is about 2 stops too low. What do you think?

I haven’t read this whole thread, but, yes, correctly exposed and processed black and white film will generally have at least 4 stops of tone values below a correctly exposed 18% gray card, and the upper limit of highlights varies from film to film, but you can usually get at least 4-5 stops over middle gray.

what you’re doing is interesting, but doesn’t necessarily directly relate to data I’ve posted online, as my information is relative to exposing a gray card through a camera lens and using an incident light meter to set exposure. That being said, if you’ve processed the film to ISO contrast, an 18% grey card will land ~0.90 log density above film base plus fog. The catch is, where middle grey lands is going to vary a lot based on developer used, agitation, temperature, and how long it was in the developer.

Adrian Bacon · Feb 6, 2022

radiant said:
Ok, new scans from "correctly exposed" tests. I wanted to share these with you.

So what you are seeing here are two strips, exposed separately but developed + scanned together. I've shifted the lower one for one slot so you can compare the densities. Yes, you guessed right. The upper one has been exposed for one stop more than the lower. When using RGB picker and comparing the tones, they are really same. Well, you can probably see it by your eyes. Remember that these are scanned at once, so their tones are relative.

View attachment 297066

I can see 4 stops under 18%, the fift stop is a bit faint. That should be in par what HP5 can do. The upper strip has 5 stops under because of the overexposure.

For highlights or stops over 18% I can count 8 stops with different tones when using RGB picker. My scanner clearly had difficult times to scan the last slots as those are very very dense.

So what you guys think of this?

+1 looking pretty good. What density is the 18% grey exposure?

Bill Burk · Feb 6, 2022

That earlier graph by radiant had Y axis units taller than X units were wide. You should have seen the first graph I drew, I thought his X series were intervals of 0.15 (they’re 0.30). I thought the contrast was impossible.

I think radiant not knowing the density of the Stouffer scale steps (having T2115 vs T2115c) leads to irregular jumps. That’s an easy fix: Have someone read the Stouffer scale on a trusted densitometer. My densitometers are all toys so I can’t offer that service.

It’s important in sensitometer design to have consistent illumination from test to test. So making tube #4 exactly 1 mcs is not “important”. radiant can leave it at the estimated 0.03 log mcs but I think it’s neat that he can adjust the mcs for each channel.

Here is a series I would like to see. In the toe of fast films they are 0.10 spacing on .05’s so results are expected below and above the 0.10 above base plus fog (better to interpolate speed if points don’t fall right on 0.10 above base plus fog)
Then some 0.15’s in the medium speed film region.
Then 0.3’s to finish up the set, landing on 0.00 which is one arithmetic meter candle second.

Channel: log mcs

16: -3.05

15: -2.95

14: -2.85

13: -2.75

12: -2.65

11: -2.55

10: -2.40

09: -2.25

08: -2.10

07: -1.80

06: -1.50

05: -1.20

04: -0.90

03: -0.60

02: -0.30

01: =0.00 (1 mcs)

Bill Burk · Feb 6, 2022

Ah, the 400 meter point isn’t represented in my series, because that would be -1.70 log mcs.

Adrian, even though you use a different way to make test exposures… your graphs are a baseline for the community. And you have done so many combinations of film and developer that you’ve built a valuable library!

Bill Burk · Feb 6, 2022

Adrian Bacon said:
+1 looking pretty good. What density is the 18% grey exposure?

0.73

Adrian Bacon · Feb 6, 2022

Nodda Duma said:
This thread is like the powerhouse of photrio densitometer wizards. Such awesomeness.

+1

Much of it is info I already know, but there are still nuggets getting dropped.

Adrian Bacon · Feb 6, 2022

Bill Burk said:
But for quality prints, 500 is a better speed to choose with 12 minute development (Rodinal 1+25).

for HP5 in replenished xtol, I landed at EI 500 too. Ilford is conservative with their speed with HP5, at ISO contrast it’s faster than 400. Interestingly, the times they give in their sheet gives contrast closer to 0.50 and consequently ~400.

Adrian Bacon · Feb 6, 2022

Bill Burk said:
Ah, the 400 meter point isn’t represented in my series, because that would be -1.70 log mcs.

Adrian, even though you use a different way to make test exposures… your graphs are a baseline for the community. And you have done so many combinations of film and developer that you’ve built a valuable library!

thx. Kind of a bummer I don’t do replenished xtol any more. Kodaks problems forced me to switch developers, at least until I’m confident that I can reliably get known good developer, and I finish running through my supply of Ilfotec DD, though, I must say, I’ve been pleasantly surprised by DD. It’s pretty good. Not the same as xtol, but I’ve actually got no complaints, and Ilford’s data sheet for it is excellent.

Adrian Bacon · Feb 6, 2022

Bill Burk said:
0.73

ok, that’s in the ballpark. I personally prefer a bit more density, but, it’s not way off.

Adrian Bacon · Feb 6, 2022

Bill Burk said:
Ah, the 400 meter point isn’t represented in my series, because that would be -1.70 log mcs.

It’d be useful to have 100, 200, and 400 meter points.

Bill Burk · Feb 6, 2022

Adrian Bacon said:
It’d be useful to have 100, 200, and 400 meter points.

I can’t imagine a better 16 step series. By deliberately missing the points of interest you are forced to interpret from the graph without confirmation bias.

Adrian Bacon · Feb 6, 2022

Bill Burk said:
I can’t imagine a better 16 step series. By deliberately missing the points of interest you are forced to interpret from the graph without confirmation bias.

true, and now that I think about it, it’s less about having the points of interest and more about looking at the whole thing.

Bill Burk · Feb 6, 2022

I think Adrian’s tests anchor at the metered point, which I take to be 10x the 0.10 above base+fog point.

He notes his graphs with both standard and Zone System conventions, illustrating the 2/3 stop difference between the methods.

So his saying 18% is short for that metered gray card placement. His gray card is 18%, but he exposes a variety of frames and graphs accordingly

Stephen Benskin · Feb 6, 2022

Bill Burk said:
I think Adrian’s tests anchor at the metered point, which I take to be 10x the 0.10 above base+fog point.

He notes his graphs with both standard and Zone System conventions, illustrating the 2/3 stop difference between the methods.

So his saying 18% is short for that metered gray card placement. His gray card is 18%, but he exposes a variety of frames and graphs accordingly

The posts have been deleted. I kind of went off on a concept that might not have really been related to what you were discussing and it wasn't very well stated either. I got a little triggered with the "in the ballpark" phrase. It gave me the impression there was a suggestion of a universal aim value. I still think this all falls under a worthy topic for further discussion: methodology and interpretation.

I took a look at a couple of the curves. They need a little explaining to properly evaluate the reference curves. It might be interesting to do a thread reviewing the curves.

Craig · Feb 6, 2022

Adrian Bacon said:
for HP5 in replenished xtol, I landed at EI 500 too. Ilford is conservative with their speed with HP5, at ISO contrast it’s faster than 400. Interestingly, the times they give in their sheet gives contrast closer to 0.50 and consequently ~400.

I noticed that as well. What I though odd was for every other Ilford film in Xtol the contrast comes out closer to 0.58 when using datasheet times.

What did you determine to be your normal HP5/replenished Xtol development time? For me it's about 9 min in a jobo at 20°C

Craig · Feb 6, 2022

Stephen Benskin said:
I think it woujld be helpful for me to address this issue better if you could give me what you consider -2, -1, Normal, +1, and +2 development and why you've determined those numbers.

Would you consider "normal" development to be one that yields a CI of 0.58 (or thereabouts)?

Stephen Benskin · Feb 6, 2022

Craig said:
Would you consider "normal" development to be one that yields a CI of 0.58 (or thereabouts)?

I consider that Normal under statistically average conditions. Yes.

But other manufacturers use different methods to determine the film gradient, so their values could be different for the same curve. It makes it hard to compare.

Adrian Bacon · Feb 7, 2022

Bill Burk said:
I think Adrian’s tests anchor at the metered point, which I take to be 10x the 0.10 above base+fog point.

He notes his graphs with both standard and Zone System conventions, illustrating the 2/3 stop difference between the methods.

So his saying 18% is short for that metered gray card placement. His gray card is 18%, but he exposes a variety of frames and graphs accordingly

Yes. It’s the exposure of an 18% gray card, evenly illuminated, with the card directly facing the camera and filling the frame. The lens is at infinity focus and has a manual clickless aperture ring on the barrel of the lens with marks for measured lens transmission. I then use an incident meter placed at the gray card to measure the light hitting it and adjust the light to match the transmission stop I have the lens set to. From there, I walk up and down the aperture scale on the lens, exposing the gray card for each stop of exposure. The light is a strobe, and I have 1/10th f stop control of the power, and it typically varies shot to shot by less than 1/10th f stop. I wouldn’t go so far as to call it calibrated, or suitable for scientific testing, but for working out development times and approximate film speed at said dev time, it easily gets you within a third of a stop with a lot of breathing room to spare.

Adrian Bacon · Feb 7, 2022

Stephen Benskin said:
The posts have been deleted. I kind of went off on a concept that might not have really been related to what you were discussing and it wasn't very well stated either. I got a little triggered with the "in the ballpark" phrase. It gave me the impression there was a suggestion of a universal aim value. I still think this all falls under a worthy topic for further discussion: methodology and interpretation.

I took a look at a couple of the curves. They need a little explaining to properly evaluate the reference curves. It might be interesting to do a thread reviewing the curves.

there’s already a thread talking about my graphs. @Bill Burk and I actually developed the graph in said thread here on Photrio. If memory serves, you even chimed in on said thread. I don’t have the link handy, but I doubt it’d be that hard to find.

with respects to “in the ballpark”, no, there isn’t a universal aim value per se, however, 0.72 is pretty close to what many zone system practitioners aim for when exposing an 18% gray card, and that is what I was referring to.

Adrian Bacon · Feb 7, 2022

Craig said:
I noticed that as well. What I though odd was for every other Ilford film in Xtol the contrast comes out closer to 0.58 when using datasheet times.

What did you determine to be your normal HP5/replenished Xtol development time? For me it's about 9 min in a jobo at 20°C

7:30 @ 24C in a jobo.

Bill Burk · Feb 12, 2022

@Adrian Bacon I stand by your chart. It shows aims of ASA and Ansel Adams on the same piece of paper.
We estimated the small distance between the red and green dots at 0.1 above base+fog. The separation exists because Zone System average aims for each Zone draw a slightly lower contrast than the ASA test contrast aims. And when you develop film a little less, the characteristic curve flattens a bit, and with it the point where the curve crosses 0.1 above base+fog moves a little to the right.

Adventures in film characteristic analysis

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