Adventures in film characteristic analysis

Bill Burk · Feb 28, 2022

@Adrian Bacon can you show @radiant our reference line for ASA, I think that will help to have an overlay with that line (and maybe the Zone System N)

radiant · Feb 28, 2022

The data here is from previous test, HP5 very overdeveloped.

I picked 7 stops (or 2.1 log) from linear part. That shows density range is log 1.3 which translates to ISO 131 and shows that I should use Grade 0 filter, so veery contrasty negative. Also we can see that to print the paper needs to be work on 4.4 stops (or 1.3 log).

Does this work this way?

Bill Burk · Feb 28, 2022

0.62 should require Grade 2 with average flare and a condenser enlarger. So use Grade 2 if you shot your photo on that part of the curve.

You would get up on that part of the curve by “overexposing” as by shooting at 250 even though you pushed the HP5+ to 1600

It’s like the straight line section of the curve refused to go along with the push.

p.s. I like the choice you made for intervals along the scale.

Adrian Bacon · Feb 28, 2022

Bill Burk said:
@Adrian Bacon can you show @radiant our reference line for ASA, I think that will help to have an overlay with that line (and maybe the Zone System N)

I've made a public version of the google spreadsheet I use for my own stuff that I share in the resources section. Here's a link: https://docs.google.com/spreadsheets/d/1FToxYMFtC-kuYKuTvUCctEAsfHio9onw4SKLpdQAVdc/edit?usp=sharing

Anybody can go make their own copy by doing file->make a copy to modify it to whatever they want. How to use it should be relatively straightforward to figure out by looking at what is done with @radiant numbers. I usually copy the tab and modify it for any emulsions/variations, etc.

I've pre-populated the HP5 numbers from @radiant, but had to move the density down by 0.8 (as a guess) simply because I'm assuming the density numbers are open gate and include film base plus fog. As a side note, @radiant it would be good to have exposure/density go down at least a few steps into film base plus fog so that it's obvious where the film base plus fog is when looking at the numbers, and also, include the film base plus fog measurement so that it can be subtracted from the other values.

Here's the image of the spreadsheet I shared above:

Bill Burk · Feb 28, 2022

Thanks @Adrian Bacon

Overlays like that help you see what you want versus what you got, so I think they are good for these graphs.

We might want to see Contrast Index overlay and Delta-X overlay in a future graph, meanwhile I think maybe a movie of me positioning the overlay on the paper will help show what it could look like. One of these days I will do something like that.

@radiant mentioned B+F separately, HP5+ 0.35 and Foma 400 0.45 and Foma 100 0.32

I usually subtract but drew my graph with absolute densities before I got the numbers.

Bill Burk · Feb 28, 2022

p.s. @Adrian Bacon your graph shouldn’t be that close to aim. HP5+ way overshot the ASA 400 1.45 absolute density was aim and he got 1.76, which I read as 0.85 Contrast Index

Adrian Bacon · Feb 28, 2022

Bill Burk said:
Thanks @Adrian Bacon

Overlays like that help you see what you want versus what you got, so I think they are good for these graphs.

We might want to see Contrast Index overlay and Delta-X overlay in a future graph, meanwhile I think maybe a movie of me positioning the overlay on the paper will help show what it could look like. One of these days I will do something like that.

@radiant mentioned B+F separately, HP5+ 0.35 and Foma 400 0.45 and Foma 100 0.32

I usually subtract but drew my graph with absolute densities before I got the numbers.

Ah... I'll revise it then.

Adrian Bacon · Feb 28, 2022

Here's the revised one. I've updated the spreadsheet as well. 0.0 density on the vertical axis is film base plus fog.

Bill Burk · Mar 1, 2022

@Adrian Bacon I think his readings span 0.40 to -2.75 log mcs, if you agree (to match my paper) move numbers in column G down 0.20

I like how you have 0.01 row intervals.

Adrian Bacon · Mar 1, 2022

Bill Burk said:
@Adrian Bacon I think his readings span 0.40 to -2.75 log mcs, if you agree (to match my paper) move numbers in column G down 0.20

I like how you have 0.01 row intervals.

I revised the previous post with the new chart and the spreadsheet has been updated. Yep. 0.01 is nice to have.

radiant · Mar 1, 2022

Bill Burk said:
0.62 should require Grade 2 with average flare and a condenser enlarger. So use Grade 2 if you shot your photo on that part of the curve.
You would get up on that part of the curve by “overexposing” as by shooting at 250 even though you pushed the HP5+ to 1600
It’s like the straight line section of the curve refused to go along with the push.
p.s. I like the choice you made for intervals along the scale.

I've only calculated ISO R with density difference, not from gamma. In that example there is 1.3 log difference in density which translates to 130 ISO R and therefore the grade (which is correct).

How does one calculate ISO R from Gamma?

And I was thinking the same; I could get to the straight part of curve only by exposing the scene by quite a bit (I mean compared to 1600). Well.. exposing normally and in this case ISO 250. Pretty dense negatives for sure The contrast is even more when exposed at 1600 because all the picture information is next to the toe. This is really interesting!

As you probably noticed the stepping was half stops down and full steps up from ISO 400 18% point. The lowest slot is quite dense still and I'm getting quite long shoulder without any use. I was thinking of changing the system to 0.75 stops up/down. That way I could get more toe and remove excessive shoulder information. What do you think about this?

Adrian Bacon said:
I've made a public version of the google spreadsheet I use for my own stuff that I share in the resources section. Here's a link: https://docs.google.com/spreadsheets/d/1FToxYMFtC-kuYKuTvUCctEAsfHio9onw4SKLpdQAVdc/edit?usp=sharing

This is cool. Thanks for sharing!

Adrian Bacon said:
I've pre-populated the HP5 numbers from @radiant, but had to move the density down by 0.8 (as a guess) simply because I'm assuming the density numbers are open gate and include film base plus fog. As a side note, @radiant it would be good to have exposure/density go down at least a few steps into film base plus fog so that it's obvious where the film base plus fog is when looking at the numbers, and also, include the film base plus fog measurement so that it can be subtracted from the other values.

This was my bad. I forgot base+fog and started to (once again) questioning my numbers in general so that is why I forgot those.

I agree that the toe should be more visible. Half stop interval was not enough to reach the bottom. One stop interval is too much. So I thought 0.75. That would give 6 stops under 18%.

I think it is a bit difficult to do the analysis if the film was actually shot at 1600 and developed 20 minutes because of the missing toe. Should I expose one strip with ISO 1600 times?

Adrian Bacon · Mar 1, 2022

radiant said:
I agree that the toe should be more visible. Half stop interval was not enough to reach the bottom. One stop interval is too much. So I thought 0.75. That would give 6 stops under 18%

if possible, I’d keep 0.15 and either give less exposure, or add additional steps, or process for less time. 6 stops below middle gray is marginal depending on the shape of the toe down there and on a long toe film you’ll still probably have measurable density happening 6 stops down, though it’ll be extremely low contrast unless you give it extremely long development time.

radiant · Mar 1, 2022

Adrian Bacon said:
if possible, I’d keep 0.15 and either give less exposure, or add additional steps, or process for less time. 6 stops below middle gray is marginal depending on the shape of the toe down there and on a long toe film you’ll still probably have measurable density happening 6 stops down, though it’ll be extremely low contrast unless you give it extremely long development time.

I could translate the few full stops into lower part giving it more steps/slots. As we have seen there are many steps on the shoulder on HP5+. I think those aren't needed?

Is there particular reason why you would like to keep it 0.15? Or just the standard way, maybe plotting papers support this or.. ?

Adrian Bacon · Mar 1, 2022

radiant said:
I could translate the few full stops into lower part giving it more steps/slots. As we have seen there are many steps on the shoulder on HP5+. I think those aren't needed?

Is there particular reason why you would like to keep it 0.15? Or just the standard way, maybe plotting papers support this or.. ?

0.15 = finer resolution. This is less important in the mid tones and highlights, but down in the toe area it’s helpful to have as many steps as possible so you can see what is happening and where it’s happening. The ISO standard allows manufacturers to round to the nearest third stop, so in an ideal world, the steps would actually be 0.1 or 0.05 apart down there, then adjust the overall exposure of everything to expose in the MCS range you’re targeting, depending on the speed of the film.

Bill Burk · Mar 1, 2022

Your least density/lowest exposure is -2.75 log mcs now, the entire series is good to study 400 speed film and 100 speed film.

You could go one interval lower to -2.9 log mcs (and sacrifice the highest exposure because the highest shoulder information isn’t absolutely needed).

I like the simplicity of the series and think that you switched from coarse to fine at a good place

Adrian Bacon · Mar 1, 2022

Bill Burk said:
Your least density/lowest exposure is -2.75 log mcs now, the entire series is good to study 400 speed film and 100 speed film.

You could go one interval lower to -2.9 log mcs (and sacrifice the highest exposure because the highest shoulder information isn’t absolutely needed).

I like the simplicity of the series and think that you switched from coarse to fine at a good place

I don't disagree. Getting to -2.9 would be helpful, and the top stop of exposure is a "nice to have" but I'd rather have the extra step at the bottom.

radiant · Mar 1, 2022

My next exposures are done, waiting for development. It will range from log -1.5 to 1.5. The lower part of 18% is 10 stops half stop stepping and upper part 5 stops in full steps (total 16). So full range is 10 stops.

And yes I'm going to try developing four different times with Bill's method

Bill Burk · Mar 1, 2022

radiant said:
I've only calculated ISO R with density difference, not from gamma. In that example there is 1.3 log difference in density which translates to 130 ISO R and therefore the grade (which is correct).

How does one calculate ISO R from Gamma?

Figure your subject luminance range, say 7 stops. Times 0.3 to make it a logarithm => 2.10

Then subtract your flare. If you don't know it, try 0.40 => 1.70

Now just relate this to your paper LER, say Grade 2 => 1.05

Gives you the contrast aim for your film development. 1.05 / 1.70 => 0.62

Another figure you may have seen, 0.58 fits with 7 1/3 stop Subject Luminance Range (minus 0.4 flare).

That was for Diffusion Enlarger. Condenser Enlargers have different aims.

This is one of the charts I refer to (Stephen Benskin gave it to me).

https://beefalobill.com/imgs/Contrast Indexes - Kodak.jpg

radiant · Mar 2, 2022

Thanks @Bill Burk, that was eye opening (again). The chart is pretty handy for sure.

radiant · Mar 2, 2022

Finally made some "serious" testing in my perspective and answered to Bills request of varying development time.

So here is HP5+ at Adox XT-3 1+1, 30 sec agitation cycle, 20degC. 6,8,12 (recommended), 18 minutes.

Base+fog at 0.35 pretty much on all strips.

I exposed a continuous film and marked the breaks with tape. That was actually a good idea. But un-reeling a bit of film was pretty sketchy. So the development times are close but not exact. Snipping a piece of film takes some time when doing it first time. But I don't think there is huge difference. Of course the 18 minute time got hit by this operation most as it was off from the normal development cycle the most.

And I really love how film looks when it is not yet fixed but developed

radiant · Mar 2, 2022

I have to say that is some crazy linear output. The test reached the toe just about. Well.. toe, I cannot see one. The lowest datapoints are under 0.1 log above base+fog. 6+8 min lowest points are base+fog. So I would call that good aiming

Shoulder is not visible, I'm quite sure it is right after the last data points. I adjusted the exposure to end at +1.5 log over Zone V (18%) to avoid loosing resolution for shoulder. I guess with 18 minutes (maybe a bit lower because of the cutting operations) doesn't yet compress the highlights as we saw with real 20 minutes developer before?

By my calculations gamma is quite about 0.6 for recommended developing time (12 minutes). The linear part is log 3.0 -> 10 stops. XT-3 and HP5+ seem to get along quite well. Gamma for 18 minutes is by my calculations 0.73.

But still a reminder, 18 minutes isn't totally right because of pauses in development.

Adrian Bacon · Mar 2, 2022

radiant said:
But still a reminder, 18 minutes isn't totally right because of pauses in development.

Once you get past 10 minutes dev time small time errors turn into almost nothing. At 18 minutes a variation of ~30 seconds is less than 3 percent, which is probably barely measurable, much less noticeable.

radiant said:
I have to say that is some crazy linear output. The test reached the toe just about. Well.. toe, I cannot see one. The lowest datapoints are under 0.1 log above base+fog. 6+8 min lowest points are base+fog. So I would call that good aiming

That's why I was saying it's generally a good idea to have at least a few steps below where you think the base+fog is so that it's obvious where the toe is. In the testing I did for HP5 I had exposures in full stop increments down to -7 or -8 (I don't remember) just so I could see a couple of base+fog steps before density started to show up.

Adrian Bacon · Mar 2, 2022

It looks like 12 minutes is just about zone contrast... though, the bottom part has some wiggles. Is that from measuring or the exposure?

radiant · Mar 2, 2022

Adrian Bacon said:
Once you get past 10 minutes dev time small time errors turn into almost nothing. At 18 minutes a variation of ~30 seconds is less than 3 percent, which is probably barely measurable, much less noticeable.

That's why I was saying it's generally a good idea to have at least a few steps below where you think the base+fog is so that it's obvious where the toe is. In the testing I did for HP5 I had exposures in full stop increments down to -7 or -8 (I don't remember) just so I could see a couple of base+fog steps before density started to show up.

I developed 5x7" sheet of Foma 100 with manual inspection (IR-video) and I was very surprised how fast the image appeared and how slowly the density grew. So it is probably very very slow after 10 minutes.

The density is so low already on these ones so I don't know if that is really worthwhile? We are talking about sub 0.1 log density. How much does that shift affect to contrast and ISO analysis? I would guess human factors are bigger (where to set the analysis points). Well, originally I was about to go down by 0.25 steps but someone here said I should go with 0.15

radiant · Mar 2, 2022

Adrian Bacon said:
It looks like 12 minutes is just about zone contrast... though, the bottom part has some wiggles. Is that from measuring or the exposure?

Well, 12 minutes is the manufacturer time so that wouldn't be a surprise.

I don't know why the wiggles (I think that is noise?). I would blame scanner+user for this, maybe the density range I've set for scanning? But one would assume low densities would actually work more steadily.. I have to check if another scan fixes that.

Adventures in film characteristic analysis

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