My adventure with FX-55 and DIY Sensitometry and Densitometry

Intro
I like to share my journey so others can hopefully profit from it as I did with other Forum posts and websites.
I would also love some feedback and help with interpretation of the data.

The goal
I like to have the ability to create H-D curves.
With them I want to get the right development times and learn about the characteristics of the emulsion. I would also like to know the right EI.

The Setup
I built a Sensitometer and a Densitometer. Maybe I will get deeper into them in another post.
I use DIY rotary development at the same speeds as a Jobo system.


Densitometer
Uses a light sensor (isl29125), Arduino, display, LED light source and a contraption to hold everything at the same place.
Its calibrated with the uncalibrated Stouffer Wedge T2115.
Repeatability is a bit loose, I guess because of the light source instability. I have no idea how commercial ones deal with this. Any idea?
I would give it a +/-10% accuracy (but not confirmed)

Foma 100
I use DIY rotary development at the same speeds as a Jobo system.




I also did some exposures with a Nikon F80s (only half stop accuracy, my F90x should be better) like Cory Miller explains here.
As I don’t trust the logE of my densitometer, I think this should give me numbers to compare to EI of the camera?
I like to use Zone 2 instead of Zone 1 because I think it gives me better real world results I care about.

FX-55 (rotary)	EI in camera	Zone	Density above Base+Fog	goal density
9min	80	2	0,09	0,24
9min	80	5	0,79	0,72
9min	80	8	1,51	1,29
6min	80	2	0,01	0,24
6min	80	5	0,51	0,72
6min	80	8	1,13	1,29
6min	50	2	0,06	0,24

Conclusion
My EI for Foma 100 with FX-55 could be around 50 and dev time between 6-9min.
Furter testing is needed, I would try 7min next.
I was really hoping to see the speed enhancing of FX-55. Maybe with other emulsions...
And I struggle a bit with the low Dmax, I’m not sure if my FX-55 is working right.

Developer	"dynamic range" Z2-Z8	Base+Fog
FX-55 6min	6,5 stops	0,26
FX-55 9min	3,5 stops	0,29
Rodinal 1+50 8min	3,5 stops	0,26

FX-55 troubles in detail
I had disappointing results at first. And I read some other people did as well...
I guess I found my problem.
The formula found at John Finch site asks for “Sodium carbonate anhydrous”.
I have (I guess) “sodium carbonate monohydrate“. The Darkroom Cookbock V3 states a multiplier of 1.17.

The orange “FX-55 error 9min” is the one with only 15,4g instead of 18g sodium carbonate mono. In partA/liter.
Interesting that its almost the same as the corrected FX-55 with 6min.

I use DIY rotary development at the same speeds as a Jobo system.


Questions
Why is the Dmax so low? Fx-55 6min is only d=1,5 above Basefog, and that part was exposed to daylight for minutes.
Is this just Foma 100 or is my methodology fundamental broken?
I also plotted the H-D curve from "the naked photographer" to my charts and it looks plausible.
I guess my data is not crazy off, but I struggle with the interpretation of it.

Thanks for your time

I think more detail about the test methodology (metering/sensitometer/densitometer/calculations) would be required in order to comment specifically on those variables, however I can make a few general comments and some observations assuming your plots are roughly ok:

1) I assume your x-axis is meant to be an arbitrary log-H scale (usually called relative log-H)?

2) Based on the data provided by Foma, the 100 speed film appears to have an ISO speed somewhere in the 80-100 range. If we assume 100, a typical Zone System EI test without flare should result in the 0.1 above FB+fog density falling on the Zone I 2/3 exposure (or an EI of approx. 64) so you can use that as something to compare with

3) On your plots the 6-minute FX-55 curves have approximately the right gradient for testing (and for validating against the ISO criteria as well). For an ISO 100 film (Zone System EI 64) the net density 0.1 should fall on the exposure 0.008 lx-s or log -2.1. This would be 3 1/3 stops below the metered exposure (ie Zone I 2/3 as indicated above)

4) Just a rough generalization but Phenidone-ascorbate developers can tend to give a somewhat more s-shaped curve (ie reduced highlight contrast) than other types of developers. Of course this is not always true.

5) Whenever you read about a film developer giving a speed increase, the magnitude is virtually always nonsense. In real terms, no general purpose developer will ever get you a speed increase of more than a small fraction of a stop, so do not be disappointed if you find most developers to give roughly the same speed +/- error.

Edited: typo

Welcome aboard @outofzone!

outofzone said:

Uses a light sensor (isl29125), Arduino, display, LED light source and a contraption to hold everything at the same place.

Click to expand...

Yes, that works, sort of; I've made something similar. The tricky bit is getting the high densities to read well. This is a fundamental challenge with this kind of approach. It doesn't help that the ISL29125 you picked is relatively crude in terms of its dynamic range and resolution. This will make it (very) difficult to reliably (accurately + consistently) read densities over 1.5 or so. Anyway, you mention having calibrated your DIY densitometer against a T2115 step tablet, so I assume you're aware of any systematic problems with your approach. I can only say from my own experience is that these problems are significant.

outofzone said:

I have (I guess) “sodium carbonate monohydrate“.

Click to expand...

Why guess?
Store-bought washing soda is either decahydrate or monohydrate. Which you get appears, interestingly, to be culturally defined. In the US, it's apparently common that washing soda is monohydrate. Here in NL, it's usually decahydrate, although a slightly more costly 'superior' soda turns out to be monohydrate.
In practice, the two can be told apart reasonably well - the monohydrate usually comes in the form of small, dry, white pellets. The decahydrate is decidedly more crystalline, feels somewhat moist and tends to clump really really badly.
One feasible way of figuring out which you have is to weight out 100g, then dry it in an oven at a little over boiling temperature for half an hour or so. At that point, you should have anhydrous sodium carbonate. Weigh it again, calculate the difference and you should have a decent idea of whether you started out with decahydrate or monohydrate.

outofzone said:

Why is the Dmax so low? Fx-55 6min is only d=1,5 above Basefog, and that part was exposed to daylight for minutes.
Is this just Foma 100 or is my methodology fundamental broken?

Click to expand...

You have your T2115, so you can compare the densities on the negatives you produced with your step tablet to rule out gross measurement problems. But I don't see anything particularly odd going on right off the bat. And yes, Fomapan 100 seems to quite easily shoulder off. If you're unsure what's going on, one thing you might try is replicate the HD curve in the Fomapan 100 datasheet. They give 3 curves, using Microphen. ID68 should give the same results if you want to DIY the developer.

I wouldn't expect miracles from FX55 (or any developer really) speed-wise. The EI of 50 you arrived at sounds entirely plausible to me.

Have fun experimenting! My compliments on the clear and comprehensive report.

Thanks, Milpool for your reply.
I have to say I struggle a bit to understand all of your answer. I’m new to this topic, can you recommend some articles/books to learn in more detail?
I got most of my information out of the “Basic Photographic Sensitometry Workbook” from Kodak.

About the Sensitometer calculations in detail
Imagine the setup like an enlarger with really accurate shutter (I use one from an Agfa Isolette). The step wedge is in contact with the film.
I measured the light that would reach the step wedge, I placed a grey card there to measure.
I got f2, 1/13sec at Iso 100
Calcuated an EV=5,7 calculated with this formula.

Calculated LUX out of it.
And now I see that there are so many different formulas for this and I have no idea which one is right. I got 28Lux out of it, but I found another one that gives 130Lux.
Do you know the right answer to this?

After this calculate the LogExposure from Lux and the actual shutter speed the Sensitometer uses which is 118ms (measured with an oscilloscope)

In the Kodak workbook the Step wedge is exposed to 3,35 log exposure (millilux seconds)
I get around 3,52.

As the Workbook does not mention negative logE I didn’t think about this possibility.
I guess my knowledge today is not sufficient to follow your point 3.

My only comment was to be that John Finch claims to have tested FX55 and finds it gives up to 2/3 rds of a stop more speed as you have said and he is usually to be trusted in what he says, having used his film speed test procedure in his earlier video which to my untrained eye looked logical. However this seems to be questioned by Milpool who says:

"Whenever you read about a film developer giving a speed increase, the magnitude is virtually always nonsense. In real terms, no general purpose developer will ever get you a speed increase of more than a small fraction of a stop, so do not be disappointed if you find most developers to give roughly the same speed +/- error."

His quote is given in very clear terms of "a fraction of a stop" which is way less than 2/3rds

There may be others who appear to believe that more than a fraction of a stop is possible so who knows who is correct

What I'd do if I were you is use John Finch's film speed test to see what you get

pentaxuser

Thanks Koraks for your answer as well.

I did the drying method to figure this out.

The resolution with the ISL Sensor gets a bit low with higher density. I plot the calibration data in excel and use a formula to calculate the density of the negatives. The result is almost perfectly logarithmic, the R2 value is around 0,9998 most of the time.
Did you research which kind of sensors commercial units use? I couldn’t figure this out, but I guess it’s more about math and temp compensation etc. that makes them more reliable.

I think my problem is more on the sensitometer side. So I’m not sure to use it for testing film speed but only to compare characteristics. But sure, it would be fun to be able to do it.

The eye method with the Stouffer wedge seems alright.


Are there anywhere real H-D Curves available? All I can find are always without absolute measurements.

@pentaxuser

As I have a couple rolls of exposed Kentmere 400 with different EI, I may divert soon to another method. I just like the idea of using a step wedge to get so much information from a small piece of film.
In my head I only must get one “real” number from a Zone? Exposed frame with a proper trusted camera to link the step wedge to useful data.

pentaxuser said:

My only comment was to be that John Finch claims to have tested FX55 and finds it gives up to 2/3 rds of a stop more speed as you have said and he is usually to be trusted in what he says, having used his film speed test procedure in his earlier video which to my untrained eye looked logical. However this seems to be questioned by Milpool who says:

"Whenever you read about a film developer giving a speed increase, the magnitude is virtually always nonsense. In real terms, no general purpose developer will ever get you a speed increase of more than a small fraction of a stop, so do not be disappointed if you find most developers to give roughly the same speed +/- error."

His quote is given in very clear terms of "a fraction of a stop" which is way less than 2/3rds

There may be others who appear to believe that more than a fraction of a stop is possible so who knows who is correct

What I'd do if I were you is use John Finch's film speed test to see what you get

pentaxuser

Click to expand...

An exposure index is not the same as film speed. You can decide on an exposure index based on whatever criteria you choose (hopefully it is based on print quality and repetition/experience).

The method OP is using is sensitometry with a fixed density criterion (Zone System). What I’m saying is that for any given film there is no developer that will literally shift that density 2/3 stops to the left on a D/log-H graph relative to what a baseline reference developer gives you (unless perhaps the reference developer is some really badly formulated concoction).

Edit: autocorrect typo

Milpool said:

An exposure index is not the same as film speed. You can decide on an exposure index based on whatever criteria you choose (hopefully it is based on print quality and repetition/experience).

The method OP is using is sensitometry with a fixed density criterion (Zone System). What I’m saying is that for any given film there is no developer that will literally shift that density 2/3 stops to the left on a D/log-H graph relative to what a baseline reference developer gives you (unless perhaps the reference developer is some really badly formulated concoction).

Edit: autocorrect typo

Click to expand...

Thanks, so the so-called speed enhancing developers such as Microphen to name one of the commercial ones which seems to claim this ability for itself is completely false as are the ones such as Perceptol which the maker recommends to be used at a stop less ?

pentaxuser

pentaxuser said:

Thanks, so the so-called speed enhancing developers such as Microphen to name one of the commercial ones which seems to claim this ability for itself is completely false as are the ones such as Perceptol which the maker recommends to be used at a stop less ?

pentaxuser

Click to expand...

I think Ilford refers to Microphen giving an “effective increase” in film speed, which I interpret to refer mostly to the slightly increased shadow/toe contrast PQ developers of that type (Kodak T-Max is another) tend to produce. I would say the characterization has more to do with EI (as indicated in the development tables) and this seems more evident where Ilford basically says the faster the film the bigger the increase in effective speed. There is probably a small increase in “real” emulsion speed but it’s not going to be anything like 2/3 stop relative to say ID-11.

I did not find Perceptol reduced speed very much vs ID-11/D-76. Here again I think Ilford is really referring to a suggested EI that plays to the characteristics of Perceptol - ie guard against overdevelopment.

The point I was trying to make was simply that OP shouldn’t be disappointed if FX-55 doesn’t slide the Fomapan 100 curve 1/2 stop to the left of an ISO 100 curve. Not going to happen.

outofzone said:

Did you research which kind of sensors commercial units use? I couldn’t figure this out, but I guess it’s more about math and temp compensation etc. that makes them more reliable.

Click to expand...

Not a whole lot, but I'd expect that units from the 1980s-2000s use photodiodes and application-specific amplification, signal conditioning & compensation circuitry. There's a nice review about a Macbeth densitometer just being posted yesterday on the forum as well; you might want to check it out. The question isn't really (or shouldn't be) about the sensor as such. What's more important is (1) the design of the optical path, (2) light source control and (3) analog signal conditioning. To a large extent, you buy this as a black box when you use something like the sensor subsystem you chose, and the choices made in this black box have pros & cons. For instance, effects like temperature variations are usually very well controlled in such integrated sensors. On the other hand, these sensors invariably are intended to give a linear (as opposed to a logarithmic) output, and that greatly affects the processing of high densities.

outofzone said:

I think my problem is more on the sensitometer side.

Click to expand...

In the sense that this may affect linearity?

For the record, I read part of your question as a doubt concerning the linearity and the severe shouldering of the curve. As regards film speed, I think the main issue there is that it's indeed tricky to establish an absolute benchmark in your setup, although again, the EI=50 number you come up with for Fomapan 100 looks by all means very realistic and plausible to me.

outofzone said:

Are there anywhere real H-D Curves available? All I can find are always without absolute measurements.

Click to expand...

For working out whether you got the curve shape right, the datasheet curves are good enough. On this forum you'll see curves being posted from time to time, but they are few and far between.

Attached a curve for Delta 100 in FX-55 copied from Crawley's original article.
I believe Crawley formulated FX-55 to give a higher mid-tone contrast. The buffer mix is unusual to get this.

Today I tested the Foma100 in 7min FX-55

I am still a bit confused about the lack of density, but the curve from "the naked photographer" also end at d=1,8.
So I guess this is just the film. I will move forward to finding the times for Kentmere 400.




Tested with Nikon F90X, Foma100, FX-55, 7min, rotary

EI	target zone	d above Base+fog	target d
50​	1​	0,01​	0,1​
50​	2​	0,08​	0,24​
50​	8​	1,33​	1,29​

Does anyone can help me with this formula to get Lux out of EV?
And any ideas on how to "calibrate" my curves to the exposures from a camera are really appreciated

outofzone said:

Calculated LUX out of it.
And now I see that there are so many different formulas for this and I have no idea which one is right. I got 28Lux out of it, but I found another one that gives 130Lux.
Do you know the right answer to this?
View attachment 393589

Click to expand...

Thank you for all your replies. I do not have enough time today but will address them later.

Thought about doing something similar myself at one point, are you using off the shelf leds? Some ive spoken too said they may be too blue, Sunlike from Seoul tech have brought out what seems to be a broad range led.

Since your well versed in Arduino Id get a lux meter and you can be more precise.

How does the rest of the testing go?

LED spectrum is the least of your worries when you make something like this. Besides, you can get pretty much every spectrum you want currently.

acrobatic_citron said:

what seems to be a broad range led

Click to expand...

These have been around for quite some time. What people sometimes worry about is the peak at the blue side of the spectrum and the dip around 500nm. Newer types don't have this, depending on the color temperature you get (higher K obviously does have a raised blue part).

acrobatic_citron said:

Id get a lux meter and you can be more precise.

Click to expand...

Why?

OP was struggling with calculating Lux, a simple arduino lux meter means no calculations and fun to install

Ah, I see; the argument is ease of use, not so much precision. I agree that if one wants to determine lux, then using this particular sensor is not the easiest way. The datasheet contains information on how to approach this. In the end, you still need a lux meter to calibrate the setup against.