Adventures in film characteristic analysis

[Adrian Bacon]

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?

Contrast and ISO analysis is all 0.1 and above, but.... for the purposes of push processing or extracting details down there, it's useful to see where there's density below 0.1 and where the film just plain stops responding at all. There is actually a point where the film just won't respond even though you've exposed it to light, and that really low density, low contrast stuff down there can be brought up a quite a bit through development without completely blasting out the highlights and depending on what you're planning to do with the negative, if digitizing it, that bottom 0.1 density will be digitized with at least a couple thousand discrete tone values. You can really stretch that 0.1 out quite a lot after the fact if you want to, which is why it's helpful to know how many stops are registering down there before the film stops responding to any light at all. Obviously, if printing in the darkroom, pretty much anything below 0.1 is basically useless and you want to expose so that zones 1-10 are on the straightest part of the curve, but if going the hybrid route or if you shoot in low light a lot, it's helpful to know where the film goes kaput and doesn't register anything.

 

[radiant]

There is constant dip on density in slots number 11-13 for 0.05 - 0.1 log. I mean if that is not a feature in the film. But of course it can be varying in light levels with my device.

Actually - I think we have seen similar shape on same slots before on my tests with Foma films too. It is not Stouffer problem either because it is visible in RGB values too. That dip is only 3 values in grayscale so it is very small. The 12 minute strip maximum RGB value is 107 (which is horrible for the resolution). The dip is about 2.8% in grayscale.

It would be probably good idea to use proper densitometer but these tests have shown that:
- it is possible to build a sensitometer from WS2812 led strip
- you can use scanner as densitometer

I'm not claiming that we are talking about professional level devices here but maybe very decent for hobbyist?

 

[Adrian Bacon]

I'm not claiming that we are talking about professional level devices here but maybe very decent for hobbyist?

This is great for what it is, and extremely educational too. Just think, you probably know more now than you did when you first started working on it. That alone makes it worth it, and sharing it here for others to see is just gravy.

 

[radiant]

This is great for what it is, and extremely educational too. Just think, you probably know more now than you did when you first started working on it. That alone makes it worth it, and sharing it here for others to see is just gravy.

Yes! And without you guys I wouldn't know what to say about the data!

Here is a scan of the 18 & 12 minute strips for no reason. I think I can see a bit of a dip on the slot 12 (counting from the most dense) or is it time to do something else

 

[Bill Burk]

Try to fix some film and see if you can get some film that’s 0.05 density base.

Then stack a few pieces of the 0.05 film to see if your idea of densities above and below 0.10 agrees with your scanner’s idea

120 or 4x5 is best to try because many 35mm are above 0.20 gray tint

 

[Bill Burk]

Here’s what it looks like on paper, including Time-CI curve and Zone System development times.

Time to get to ASA parameters may be 13:15
Time for Zone System N may be 10:30

 

[radiant]

Time to get to ASA parameters may be 13:15
Time for Zone System N may be 10:30

Thank you again Bill for making the analysis. That is so valuable!

I'm still thinking could the ASA parameters got hit by pauses in the agitation. The pauses were maximum 1 minute in some time target as I was messing around with wet film, lost scissors etc. I would guess the emulsion soaks in some developer which works even not submerged in developer. Maybe the hit is small.

The more I've now done the tests the more I start to like zone system and respect the film capabilities and question my constant pushing. I start to understand my problems when printing in darkroom. However pushing gives HP5+ nice contrast boost as it is so linear film otherwise on XTOL. Rodinal had a bit more S-shape curve but pushing with Rodinal seems a very bad idea.

There isn't limitless play in terms of contrast and gamma if one wants to make good prints in darkroom. Multigrade papers just cannot chew everything you throw at them.

 

[radiant]

My "densitometer" got a real job!

Long story short; I needed to mix some Foma Excel because of problem with my XT-3 batch. However the Excel mixing was not complete; I actually got two problematic Excel - mixes where all of the powder didn't mix straight away like before. So I left puzzled if my stock solutions work at all? What if that messes my precious negatives?

So I exposed a strip with previously examined steps and developed in "problematic" Excel developer. The strip came out fine by visual inspection. Job done!

It was so easy to do that I could use my device more ofter for scenarios like this. When if I mix up new 5L batch, I could just quickly check that it works as should for mental sanity.

 

[Bill Burk]

Haa yes. That’s process control. You can do it any time you want

 

[radiant]

Haa yes. That’s process control. You can do it any time you want

This is actually quite surprising project.

 

[radiant]

I changed the exposure scheme a bit to one Bill suggested; making two strips. One for the lower part of 18%/ZoneV and one for the upper part. So in total I got 31 steps. I exposed with half stop difference / 0.15 log. In total the exposure is now 16 stops or 4.8 log.

Also I changed the lux-second calculation to use 8 / ISO (instead of 10/ISO).

I ended up with this kind of data:

Toe:

My scanner seem to have troubles with the most dense part:

 

[radiant]

BTW: About MCS / log-lux seconds. I tried to get that now right.

For calculation reference: the lowest point at -3.0536 with density 0.4 gets 0.88 log lux seconds (which on my device is 4.4 milliseconds). Mid-gray / 18% / GradeV is at -1,699.

I have to visually inspect but I guess there isn't any signs of other steps under that -3.056. That makes 6 slots blank.

 

[Stephen Benskin]

You fought it all the way, but you finally have what looks like a film curve.

 

[radiant]

You fought it all the way, but you finally have what looks like a film curve.

Thanks Stephen! It has been a process for sure..

But what curve? I see film line. Damn that is crazy film+dev combo.

 

[Adrian Bacon]

I changed the exposure scheme a bit to one Bill suggested; making two strips. One for the lower part of 18%/ZoneV and one for the upper part. So in total I got 31 steps. I exposed with half stop difference / 0.15 log. In total the exposure is now 16 stops or 4.8 log.

Also I changed the lux-second calculation to use 8 / ISO (instead of 10/ISO).

I ended up with this kind of data:

View attachment 299956

Toe:

View attachment 299957

My scanner seem to have troubles with the most dense part:

View attachment 299958

Looks good. Just looking at the chart you posted, it looks like you have about 0.2 log lux seconds of exposure in density below about 0.1 density before things peter out and just stops responding to light. Nice.

 

[radiant]

Looks good. Just looking at the chart you posted, it looks like you have about 0.2 log lux seconds of exposure in density below about 0.1 density before things peter out and just stops responding to light. Nice.

Edit: messed up milliseconds / seconds.

Adrian I cannot still wrap my head around with this, can you explain how you came up with that number?

 

[radiant]

I just remembered that the previous test are developed with 1 litre Excel batch where I messed a bit with the mixing because of problems with the dissolving of powders. I mixed the powders to 0.75 litres of water and then used that directly on 1+1 mix. I used 250ml of the stock and realized after that later on. So I tried to make up the batch afterwards, adding the missing water (minus used the stock).

So .. there is a chance that the strip isn't developed over/under just a bit. I'm measuring 0.6-0.7 gamma so it might be quite OK. But just as disclaimer.

 

[radiant]

I've also added some features to my web tool: https://jouni.kapsi.fi/filmgraph/

 

[Adrian Bacon]

Edit: messed up milliseconds / seconds.

Adrian I cannot still wrap my head around with this, can you explain how you came up with that number?

In your graph (below), FB+F is sitting at ~0.35 density, which puts the speed point (which is 0.1 above FB+F) at ~0.45 density. At ~0.45 density, you're at ~-3.0 (closer to -0.2975, but we'll round to -0.3) log lux-seconds and you hit film base plus fog at ~-3.2 log lux-seconds, which is ~0.2 log lux seconds of exposure sitting down below the speed point. 0.2 log lux seconds is 2/3rds of a stop of exposure. It's very low contrast (about 0.50 gamma) and not that usable if printing in the darkroom (meaning I wouldn't normally be exposing things so that shadow detail I cared about what down in there), but if going a hybrid approach, can be stretched out from the 0.1 amount of density it's using to 0.2 density.

At least that's how I read it, assuming the chart is correct.

 

[radiant]

In your graph (below), FB+F is sitting at ~0.35 density, which puts the speed point (which is 0.1 above FB+F) at ~0.45 density. At ~0.45 density, you're at ~-3.0 (closer to -0.2975, but we'll round to -0.3) log lux-seconds and you hit film base plus fog at ~-3.2 log lux-seconds, which is ~0.2 log lux seconds of exposure sitting down below the speed point. 0.2 log lux seconds is 2/3rds of a stop of exposure. It's very low contrast (about 0.50 gamma) and not that usable if printing in the darkroom (meaning I wouldn't normally be exposing things so that shadow detail I cared about what down in there), but if going a hybrid approach, can be stretched out from the 0.1 amount of density it's using to 0.2 density.

Ah, now I understand. Yes, that is very low on shadows. It is under Zone I point.

Why anyone would like to use that area for shadows? Even pushing to 1600 and with SBR 7 stops your shadows cannot reach that point, if I looked correctly. And what do you mean by hybrid approach? Sorry for asking questions all the time

I got the same data drawn on my webtool:

 

[radiant]

Adrian I read what you wrote previously (forgot to respond) and measured again. I understand you now.

Actually Zone I (ISO 400) point is very close to 0.1 above f+b, 0.088 or 0.3 stops.

However if SBR is 7 stops + taking account flare and one uses "normal" development, then you are pretty far even with few stops pushing?

 

[Adrian Bacon]

And what do you mean by hybrid approach?

Hybrid means digitize it and linearize it in the computer, then print it out via inkjet (or display via some other means).

 

[Adrian Bacon]

Why anyone would like to use that area for shadows?

Normally you wouldn't, but if shooting in really low light or at night, its helpful to know how much is going to register so you can add development time to try to bring it up if you need to. It's more about having that information about how the film responds so in the event you end up in a less than ideal situation, you know what you can reliably get, and what you can squeeze out if you have to.

 

[radiant]

Normally you wouldn't, but if shooting in really low light or at night, its helpful to know how much is going to register so you can add development time to try to bring it up if you need to. It's more about having that information about how the film responds so in the event you end up in a less than ideal situation, you know what you can reliably get, and what you can squeeze out if you have to.

I see. On other films I have seen much more pronounced toe, that actually protects / hints of users going on that area - kind of. With HP5+ and Xtol it is so linear it basically goes straight in and cuts off the lights.

 

[Bill Burk]

Here’s a paper graph. I measure 0.57 CI and just a tad short of ASA parameters.

@radiant you and I have been discussing where I think exposure falls vs where your nominal device exposure is designed to fall.

I continue to estimate the exposure which would cause HP5+ to meet 0.1 above base plus fog is -2.70 log mcs. The curve crossed 0.1 above base plus fog right between two of your tubes. But I estimate that actual exposure is 0.01 or 0.02 higher because you didn’t hit ASA parameters.

So I think the tube you labeled -3.056 is -2.76 or -2.77 and the tube you have labeled -2.9031 is -2.62 .

We can surmise why the effective exposure seems to be higher than the engineered exposure, but I think the factor(s) will reveal themselves as you do more and more tests.

Spectrum reaching the film could be “more actinic” than daylight through glass lenses of a camera (UV could be hitting the film? Does your diffuser pass UV?).

You have a chance to try R G and B separately.

Have you electronically isolated the LED’s so there’s no noise or trace voltage that could be weakly energizing the LED’s that are supposed to be off?