CATLabs X Film 80 Characteristic Curve

Adrian Bacon · May 27, 2019

For those that are interested, here's a first workup of what the characteristic curve looks like for CATLabs X Film 80.

It was generated with what tools I have available to me, and while not scientific by most measures, gives a reasonable approximation of what to expect if shot and developed using a similar development setup as me.

The development setup:
Replenished XTOL, developed in a JOBO with constant agitation at 24C for 10:00 even. The XTOL is in a 2.5 liter bottle and is replenished with 70ml of new for every 80 square inches of film run through it.

The green line is the zone system contrast curve, the red line is ISO standard contrast curve, the yellow line is what X Film 80 is doing. The vertical axis on the left is film density in log units, 0.000 is film base plus fog. The horizontal axis along the bottom is relative exposure of an 18% grey card in full stop increments with the card filling the entire frame and the lens at infinity focus. The zero point on the horizontal axis is the exposure index for a correctly exposed 18% grey card, so horizontally to the right is the grey card given more exposure, and horizontally to the left is the grey card given less exposure, in full stop increments. -4EV on the left side of the horizontal exposure axis is placed 0.1 log density units above film base plus fog and is the speed point for the red and green lines.

I can very reliably control the amount of light hitting the grey card to within a 1/10 of stop up and down the exposure scale. It's not without error, but it's consistently very close.

So, looking at it, I'd say that with Replenished XTOL at 24C in a JOBO, X Film 80 is more like EI 64 film. At EI 80, -4EV down has a density unit of 0.040. Even though 0EV is hitting the correct zone system point, adding development time to try to bring the shadows density up a bit will just make the highlights that much more denser.

I'll probably do one more round where I add a third of a stop to make it EI64 and pull the development time in to 9:00 minutes and post that. I suspect that EI64 and 9:00 minutes is strike zone territory.

Adrian Bacon · May 27, 2019

Here's the curve for EI64. I stopped at 0EV because its about figuring out the development time and exposure needed for the shadow detail. The highlights are always going to be more contrast with constant agitation. I'd say at EI 64, 9:00 in a JOBO at 24C is probably the maximum time as EV0 easily hits ISO contrast at 0.861 density. It could probably be better at 8:00 and EI 64, though the speed point is 0.095 density, so it's just barely hitting the speed point at EI64 and 9:00.

Enjoy!

Richard Man · May 28, 2019

Yes, but the $6.40 question is "which film is it closest to?"

Thanks for the good work!

Adrian Bacon · May 28, 2019

Richard Man said:
Yes, but the $6.40 question is "which film is it closest to?"

Thanks for the good work!

Some people seem to think it’s GP3. I’ve never done this exercise with GP3 and don’t have any on hand. I’d be happy to do the same thing at EI64 and 9 minutes and post the results here if somebody is willing to donate a roll or two.

Richard Man · May 28, 2019

Can you handle 4x5? If so, I can send you a few sheets

Adrian Bacon · May 28, 2019

Richard Man said:
Can you handle 4x5? If so, I can send you a few sheets

Yes, though I’d very much prefer it in 120 roll as it’s easier to control the exposure, and I make 12 exposures to generate the 0EV to -7 EV portion of the curve. 3 exposures at 0EV, 1 at -1, -2, and -3, then 3 at -4, and one for each step below that until I run out of film or light, whichever is first, so if you send sheet, I’d need ~12 sheets. The 0 and -4 EV exposures are read and averaged between the 3 exposures of each, so the value isn’t a single shot fluke, but very likely to be very close to correct if not right on.

bascom49 · May 28, 2019

Thanks for posting your data, results and methods, very well explained and easy to follow.
Not having a lot of experience with film plots, where did you get the ISO reference and Zone reference data ?

Thanks,
Charles

bascom49 · May 28, 2019

Adrian Bacon said:
Some people seem to think it’s GP3. I’ve never done this exercise with GP3 and don’t have any on hand. I’d be happy to do the same thing at EI64 and 9 minutes and post the results here if somebody is willing to donate a roll or two.

Based on CatLabs original description, it seems that the same manufacturer that coats GP3 also coats this film for CatLabs using their specs/formula.
Which is why some of the materials like backing paper and film base look to be the same or similar to GP3.

Thanks to CatLabs for bringing a new film formulation to the market.

Charles

Adrian Bacon · May 28, 2019

bascom49 said:
Thanks for posting your data, results and methods, very well explained and easy to follow.
Not having a lot of experience with film plots, where did you get the ISO reference and Zone reference data ?

Thanks,
Charles

The ISO reference data came from the ISO standards group. ISO contrast is 1.3 log units of exposure in 0.8 log units of density starting at 0.1 log units above film base plus fog. 0.8 / 1.3 is a gamma of 0.6153. From there, it’s a little math to figure out each full stop step stating at 0.1.

For the zone system data, I actually got it from here on Photrio. Another user, @RalphLambrecht has posted it a number of times over the years. It also pops up on google in a few places if you search for it.

Adrian Bacon · May 28, 2019

bascom49 said:
Based on CatLabs original description, it seems that the same manufacturer that coats GP3 also coats this film for CatLabs using their specs/formula.
Which is why some of the materials like backing paper and film base look to be the same or similar to GP3.

Thanks to CatLabs for bringing a new film formulation to the market.

Charles

Yep. My goal is not to pass judgment, but to provide information. There is nothing wrong if it is GP3. That’s their way to support film while giving people an opportunity to also support them.

Nodda Duma · May 28, 2019

Thanks, Adrian. Explains why the sheets I developed this morning were so thin. Thought I might have done something wrong but your data confirms my results.

I recommend a five-minute pre-soak, btw, to get rid of the dyes in the anti-halation layer.

-Jason

Adrian Bacon · May 28, 2019

Nodda Duma said:
Thanks, Adrian. Explains why the sheets I developed this morning were so thin. Thought I might have done something wrong but your data confirms my results.

I recommend a five-minute pre-soak, btw, to get rid of the dyes in the anti-halation layer.

-Jason

Just out of curiosity, what you expose it at and run it at?

Nodda Duma · May 28, 2019

I spot-metered at ASA 80 on a gray-card in front of ny subject. Exposure was like 1/200s (so no reciprocity concerns). Developed in HC-110 dil B for 8:45 per the recommended dev times.

Adrian Bacon · May 28, 2019

Nodda Duma said:
I spot-metered at ASA 80 on a gray-card in front of ny subject. Exposure was like 1/200s (so no reciprocity concerns). Developed in HC-110 dil B for 8:45 per the recommended dev times.

I don’t know if hc110 gives any more or less speed than replenished XTOL (probably less), but if you weren’t metering through the lens, you have to compensate for the light lost for focusing closer than infinity. This is typically 1/3+ depending on the lens and how close you’re focusing.

If you were going through the lens, then I’d give it at least 64, though 50 would probably be better with hc110 as it’s not exactly known for being a speed demon of a developer.

EDIT: never mind, you said you shot sheets. You have to do bellows compensation in addition, so spot metering on a gray card at EI 80 won’t be nearly enough light, even with replenished XTOL.

Nodda Duma · May 28, 2019

This isn’t exactly the first sheet of film I’ve ever shot. In fact I also generate characteristic curves for the dry plates I sell worldwide. So assume that exposing at ASA 80 implies that I was shooting in conditions that didn’t require compensation, adjustments, etc.

HC-110 loses about a half stop in development. This stuff was more like 1 to 1.5 stops thin. So it almost acted like it wanted to be metered at 32. 50 might be ok.

Adrian Bacon · May 28, 2019

Nodda Duma said:
This isn’t exactly the first sheet of film I’ve ever shot. In fact I also generate characteristic curves for the dry plates I sell worldwide. So assume that exposing at ASA 80 implies that I was shooting in conditions that didn’t require compensation, adjustments, etc.

Ahh... didn’t know. You’d be amazed at how many people totally miss bellows extension and complain that some film isn’t actually as fast as it is, or don’t know that you lose some amount of light through the lens. I develop film for other people, and it happens all the time.

If it looked that under, I’d suspect that the time listed for HC110 probably isn’t quite right in addition to not being as fast. Usually if it’s not enough time, the speed point will be low and the normal gray card exposure will be low.

I have some hc110 on hand. I might do a curve for hc110. I was thinking of doing one for D-76 at 20C with inversions in a Paterson tank, so HC110 or even Rodinal wouldn’t be that big of a deal. It’d be a roll of film for each to do 0EV to -7EV.

If anybody wants to see something specific, I’m OK with doing one or two more developers, though it would be a sanity check to see how close the listed times are, and not a workup to figure speed and real dev time for that developer. I only did that with replenished XTOL because that’s my standard developer.

Nodda Duma · May 28, 2019

I just mixed up an old can of Microdol-X and developed a couple plates in it. Came out nice. I’d be tempted to try the Catlabs in it but have no idea where to start for a developing time

Adrian Bacon · May 29, 2019

Nodda Duma said:
I just mixed up an old can of Microdol-X and developed a couple plates in it. Came out nice. I’d be tempted to try the Catlabs in it but have no idea where to start for a developing time

I don’t have any Microdol-X on hand, but do have D-76, X-TOL, DD-X, HC-110, Rodinal, Ilfosol 3, and a 1 liter packet of Microphen on hand at the moment plus raw ingredients to make a couple of basic developers for experimental purposes. I can within reason acquire most things as long as I can get small enough amounts to use it before it goes off.

I’ve always wanted to try running bw through C-41 with bleach bypass just to see what it does.

Adrian Bacon · May 29, 2019

Here are some sample images. I shot them on a Hasselblad 500 C/M. I added a third to EI50 to account for the light I'd lose through the lens when focusing closer than infinity, ran them through my scanner setup and applied a basic 0.615 gamma tone curve in simple image tools. It was developed in Replenished XTOL at 24C for 9:00 and JOBO agitation. In Lightroom I adjusted the exposure, spotted for dust, and pulled the highlights down a smidge for a couple of the frames.

A few of the frames are similar to ones I've taken before, a few of them are newer compositions. I mostly zone focused, so don't expect them to be razor sharp.

Henning Serger · Jun 1, 2019

Hello Adrian,

Adrian Bacon said:
The ISO reference data came from the ISO standards group. ISO contrast is 1.3 log units of exposure in 0.8 log units of density starting at 0.1 log units above film base plus fog. 0.8 / 1.3 is a gamma of 0.6153. From there, it’s a little math to figure out each full stop step stating at 0.1.

For the zone system data, I actually got it from here on Photrio. Another user, @RalphLambrecht has posted it a number of times over the years. It also pops up on google in a few places if you search for it.

as doing sensitometric tests is a test procedure I am doing very often and for a very long time now (also for film, paper and photo chemistry manufacturers as "double-check" for R&D and QC purposes) in my independent test lab, I may have some additional info which could be helpful for you.
As you have correctly said, the values for the ISO norm characteristic curve and the values photographers mostly use when using the Zone System are a bit different. Zone system photographers mostly emphasize on keeping a relatively high level of both shadow and highlight detail.
The ISO norm is more a kind of "compromise" of shadow detail, highlight detail, speed and the different methods used in the following imaging chain getting the final (positive) picture.
As we have in general five different ways to reach the final image:
- contact printing
- optical enlarging with a pure condensor enlarger
- optical enlarging with a "mixed system": diffusion box and double-condensor
- optical enlarging with a pure diffusion system
- scanning.
And depending on the way you use the gradation differs to get perfect results.
In terms of the Zone System the ISO norm curve represents a "N+1" curve. There is an excellent explanation and description of that in the excellent book of photographer and physician Dr. Otto Beyer ( https://www.fotografie-in-schwarz-weiss.de/neuigkeiten/154-buch-belichtung.html )

So the "target values" are dependent on the workflow one uses to get the final positive picture. General rule: Lower gradation / less contrast with using condensor enlargers (and scanning), higher gradation / more contrast using diffusion systems.
And the values are also dependent on the look you want. Therefore there are also by Zone System experts different recommendations for the values of the zones:
In the attachment you'll find some recommendatios by several Zone System experts (master printer and chemistry manufacturer W. Moersch; Kunze = former manufacturer of densitometers; Foto&Labor = former darkroom print magazine; Lambrecht/Woodhouse = values from their last book; M. Anzinger - German darkroom author and engineering professor).
I hope that is helpful or interesting for you.

Best regards,
Henning

Adrian Bacon · Jun 1, 2019

Henning Serger said:
Hello Adrian,

as doing sensitometric tests is a test procedure I am doing very often and for a very long time now (also for film, paper and photo chemistry manufacturers as "double-check" for R&D and QC purposes) in my independent test lab, I may have some additional info which could be helpful for you.
As you have correctly said, the values for the ISO norm characteristic curve and the values photographers mostly use when using the Zone System are a bit different. Zone system photographers mostly emphasize on keeping a relatively high level of both shadow and highlight detail.
The ISO norm is more a kind of "compromise" of shadow detail, highlight detail, speed and the different methods used in the following imaging chain getting the final (positive) picture.
As we have in general five different ways to reach the final image:
- contact printing
- optical enlarging with a pure condensor enlarger
- optical enlarging with a "mixed system": diffusion box and double-condensor
- optical enlarging with a pure diffusion system
- scanning.
And depending on the way you use the gradation differs to get perfect results.
In terms of the Zone System the ISO norm curve represents a "N+1" curve. There is an excellent explanation and description of that in the excellent book of photographer and physician Dr. Otto Beyer ( https://www.fotografie-in-schwarz-weiss.de/neuigkeiten/154-buch-belichtung.html )

So the "target values" are dependent on the workflow one uses to get the final positive picture. General rule: Lower gradation / less contrast with using condensor enlargers (and scanning), higher gradation / more contrast using diffusion systems.
And the values are also dependent on the look you want. Therefore there are also by Zone System experts different recommendations for the values of the zones:
In the attachment you'll find some recommendatios by several Zone System experts (master printer and chemistry manufacturer W. Moersch; Kunze = former manufacturer of densitometers; Foto&Labor = former darkroom print magazine; Lambrecht/Woodhouse = values from their last book; M. Anzinger - German darkroom author and engineering professor).
I hope that is helpful or interesting for you.

Best regards,
Henning

Thank you, yes.

I included the two reference curves to serve as kind of a guidepost for upper and lower limits of contrast for normal development. Ideally you want to have at least as much contrast as the zone system contrast, and probably not more contrast than ISO contrast for a normal negative. In my experience, very few film curves are actually straight as an arrow when doing replenished xtol and constant agitation, so if I can get it to hit where the shadows are at least zone system and the highlights are roughly ISO, then I’m personally happy.

In terms of the zone system reference curve, I knew there was more than one. Gotta pick one. I picked Lambrecht/Woodhouse as that was least likely to cause a ruckus here oh photrio. If somebody prefers a different curve, that’s fine. They can take what I’ve published as a starting point to get to their preferred contrast.

Adrian Bacon · Jun 4, 2019

Based on a recent discussion here on Photrio: https://www.photrio.com/forum/threads/ilford-fp4-characteristic-curve.167806/ I've updated the graph for this film. If you want to read through the why's of where each point on the graph is, feel free to read through that discussion, otherwise, this is the characteristic curve at close enough to ISO contrast to show the speed of the film. You'll want to pull the development time in if you want to do zone system, so this is should be used as a starting point.

m00dawg · Aug 26, 2019

9:00 at 24C for XTOL Replenished seems high to me. I tried X at EI80 and 7:30/20C. It's a bit thin but the highlights seemed ok? I think it could stand to have a bit more time but mostly the shadows were lacking which makes me think at those times I should shoot it closer to 50 perhaps? I was thinking of trying the 1:1 times (10:30) though I found for other films using my rotary the times seem closer to stock XTOL times than 1:1. This is at 45 RPM using a jobo tank but my own custom motorized rotary.

I'm using sheets here. I don't yet have a great way to plot a curve but I think it'd be the best option here rather than just guessing as I am doing.

Andrew O'Neill · Aug 26, 2019

Adrian Bacon said:
Here's the curve for EI64. I stopped at 0EV because its about figuring out the development time and exposure needed for the shadow detail. The highlights are always going to be more contrast with constant agitation. I'd say at EI 64, 9:00 in a JOBO at 24C is probably the maximum time as EV0 easily hits ISO contrast at 0.861 density. It could probably be better at 8:00 and EI 64, though the speed point is 0.095 density, so it's just barely hitting the speed point at EI64 and 9:00.

Enjoy!

View attachment 224353

That curve is quite similar to what I get with HP5. I appreciate its steep shadows and lower contrast in the higher values.

Adrian Bacon · Aug 26, 2019

m00dawg said:
9:00 at 24C for XTOL Replenished seems high to me. I tried X at EI80 and 7:30/20C. It's a bit thin but the highlights seemed ok? I think it could stand to have a bit more time but mostly the shadows were lacking which makes me think at those times I should shoot it closer to 50 perhaps? I was thinking of trying the 1:1 times (10:30) though I found for other films using my rotary the times seem closer to stock XTOL times than 1:1. This is at 45 RPM using a jobo tank but my own custom motorized rotary.

I'm using sheets here. I don't yet have a great way to plot a curve but I think it'd be the best option here rather than just guessing as I am doing.

EI64 and 9 minutes gives pretty close to ISO contrast. If you want more like zone contrast, still expose it at 64, but pull 30 to 60 seconds out of the development time, 7:30 is probably a bit short for 64, but might be fine for 50.

CATLabs X Film 80 Characteristic Curve

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