Is it possible to make a DIY LED splitgrade system?

[kuhyraco]

Hello,

I had a chance to briefly see the Heiland Splitgrade system in action and I would really like it for some applications. But the price of the solution and the light source is out of my reach right now.
But I wonder how difficult it would be to put something like that together? I'm assuming it wouldn't be that fancy and comfortable.

It doesn't even have to be a fully automatic system. Let's say I have a basic electronic and programming skills and some of the following equipment:

Darkroom Automation Meter /RH Designs ZoneMaster/ another meter for measuring light levels.
Reflection densitometer for measuring density on paper.
Light source with suitable blue and green LEDs (maybe red for easel work) with PWM dimming.
Microcontroller (ESP32, Arduino MEGA) for light control and exposure management.

So i have the ability to measure/calibrate the paper and control exposure to blue and green light.

How to find out the parameters for splitgrade? Does anyone have an idea?
Thank you very much.

 

[Nicholas Lindan]

Although "Splitgrade" doesn't have a formal definition, the technique traditionally revolves around a system of making two test strips, one with all green light and one with all blue light, to determine exposure and paper grade/VC filtration. You then make the final print with two exposures to blue and green light.

Using blue & green LEDs with PWM intensity control isn't splitgrade - it is an LED variable contrast head. You would have a dial or Arduino setting to control the ratio of blue & green light intensities to give a reasonable range of paper grades. Of course nothing precludes using an LED head to do traditional splitgrade printing.

You might find the Darkroom Automation application note on metered splitgrade printing interesting http://www.darkroomautomation.com/support/appnotesgmeasured.pdf - along with an application note on how VC papers work http://www.darkroomautomation.com/support/appnotevcworkings.pdf

 

[koraks]

Forget about official "grades" as they are just fairly arbitrary ranges of ISO-R. To "calibrate" your grades, all you need is a Stouffer step tablet and some paper. You can define the grades as a combination of blue and green exposure within your specific implementation of a light source.

W.r.t. the light source, for b&w multigrade you can use whatever arrangement of blue and green LEDs you like. These can be strips, stars, individual (smd) LEDs on a PCB, COB etc. Whatever you choose, you'll have to make a light path that results in even exposure of the negative. Duffusion-based systems are easy to make; just experiment a bit with LED arrangement and e.g. milky plexiglass.

As to the controller, use any old Arduino etc of your choice with and LCD hooked up to it and buttons, rotary encoders and keypads as you see fit. Making a simple timer with two PWM outputs isn't very complicated.

This is a pretty straightforward project that many have undertaken; it's definitely feasible, just get cracking and have fun!

 

[kuhyraco]

Although "Splitgrade" doesn't have a formal definition, the technique traditionally revolves around a system of making two test strips, one with all green light and one with all blue light, to determine exposure and paper grade/VC filtration. You then make the final print with two exposures to blue and green light.

Using blue & green LEDs with PWM intensity control isn't splitgrade - it is an LED variable contrast head. You would have a dial or Arduino setting to control the ratio of blue & green light intensities to give a reasonable range of paper grades. Of course nothing precludes using an LED head to do traditional splitgrade printing.

You might find the Darkroom Automation application note on metered splitgrade printing interesting http://www.darkroomautomation.com/support/appnotesgmeasured.pdf - along with an application note on how VC papers work http://www.darkroomautomation.com/support/appnotevcworkings.pdf

But I really meant splitgrade. From the Heiland site: Exposure in 2 phases with soft and hard light allows dodging in either the hard or the soft gradation phase.

That's what I'd like to achieve. Measure the scene and get separate values for blue and green exposure that will lead me to a solid work print.

 

[kuhyraco]

Forget about official "grades" as they are just fairly arbitrary ranges of ISO-R. To "calibrate" your grades, all you need is a Stouffer step tablet and some paper. You can define the grades as a combination of blue and green exposure within your specific implementation of a light source.

W.r.t. the light source, for b&w multigrade you can use whatever arrangement of blue and green LEDs you like. These can be strips, stars, individual (smd) LEDs on a PCB, COB etc. Whatever you choose, you'll have to make a light path that results in even exposure of the negative. Duffusion-based systems are easy to make; just experiment a bit with LED arrangement and e.g. milky plexiglass.

As to the controller, use any old Arduino etc of your choice with and LCD hooked up to it and buttons, rotary encoders and keypads as you see fit. Making a simple timer with two PWM outputs isn't very complicated.

This is a pretty straightforward project that many have undertaken; it's definitely feasible, just get cracking and have fun!

I've been browsing through Photrio and seen various tutorials (including yours), which are great.

But no one has addressed splitgrade, i.e. divided exposure and after calibration without the need to make test prints.

 

[tcolgate]

Silvergrain Classics have an article on the widget you are referencing. https://silvergrainclassics.com/en/2021/09/what-is-the-heiland-splitgrade-controller/

It feels a bit like it's on the wrong side of technological diminishing returns. If you can calibrate you print setup (so know your filter factors for your grades), you can easily determine a standard grade for a single grade print with a single test strip (DistPhoto on yourtube has some videos discussing this with is Perfect Test Strip printer, but his widget isn't needed).

For multigrade you don't have to stick with just 00 and 5, you cam mix whatever you need with dodging and burning. But if you need to split grade, you're already way beyond the point where you are going to get away with one test strip, regardless of how much wizadry is in the box.

It just doesn't feel like the computer is winning you much. It's also seems to suggest you can do away with testing because it has some paper and developer know how, but realistically you're have to test because there are just too many other variables (your water, your dev temperatures).

 

[koraks]

But no one has addressed splitgrade, i.e. divided exposure and after calibration without the need to make test prints.

The whole point of split grade is to be able to burn & dodge during either or both of the separate exposures. That's almost by definition an empirical, intuitive process based on trial & error. If you want to do measurements on the negative to determine the single ISO-R grade that will encompass these measurements within the tonal scale on a single print, then that's not necessarily a split grade endeavor; it's basically just a multigrade/variable contrast approach where you replace a series of test strips by a measurement combined with calibration. Whether you then make the final exposure as a single exposure with both blue & green at the same time, or consecutive ones, really doesn't matter from the viewpoint of the paper. It does matter of course if you're going to burn & dodge, but then the question is what the added value of the initial measurement and the whole calibration circus would have been.

It just doesn't feel like the computer is winning you much.

Indeed, I agree.

 

[Pegajoy]

I do not want to step into the discussion of pro/con split grade and how it works - others are more experienced in that.
The only reason that Mr. Heiland used the split grade system was technical. At the beginning of his system, no usable LEDs were available. For the traditional enlarger head modifications that he partially still provides, it was much more easier to implement 2 filters that switches than 14 for half grades. And also calibration is not as complicate.

 

[RalphLambrecht]

I think you might be undeestimating the software involved in ÍSplit/Grade system but you shouldbe able to put a VC LED head together. The cost of the Heiland has its justification. It includes years of R&D.

 

[tcolgate]

Microcontroller (ESP32, Arduino MEGA) for light control and exposure management.

Having recently just implemented a darkroom timer on an atmega328p, given the choice, I'd opt for something slightly chunkier in terms of ram and flash support. Just about anything really bigger than an arduino really.
If I wanted to keep things tiny and cool I'd give the BBC microbit a go. I think it has everything I'd need and just a bit more than the atmega has to give headroom for more features without all the hassle of a Pi.
I think you can do a lot on an arduino if you want to stick with C/C++ (I'm spending my spare time writing C again though), but there are some things I'd like to do that start building up a bit. Like I'd quite like to be able to keep print profiles on an SSD that I could quickly switch in and out. Drivers and filesystem for that are going to eat into 32kb pretty quick. Honestly though, the idea of doing anything in C nowadays feels more than I can be bothered with for a hobby project nowadays.

 

[koraks]

Just about anything really bigger than an arduino really

You're referring specifically to the 'old-school' Arduinos like the Nano, Uno (first version) and Pro Micro. Note that there are many Arduino boards that have far more powerful controllers with more flash and RAM. 'Arduino' is really just a brand name and the product range is very extensive.

the atmega

Likewise, there are ATMega controllers with more flash and RAM than the '328P/PB.

the idea of doing anything in C nowadays feels more than I can be bothered with for a hobby project nowadays.

AI is getting pretty good at writing embedded C++.
If you want higher-level language support, it's indeed a good idea to scale up the hardware.

I've run a color enlarger controller based on an Arduino Nano for a few years; it ran 3 color channels, timer programs for b&w and color mode and read out several encoders. This ran easily within the memory constraints of a '328P. However, given the negligible cost of far more powerful hardware (e.g. ESP32 platforms), I agree it's unnecessarily limiting to stick with the very old 328P/PB platform.

 

[tcolgate]

[adrduino etc]

absolutely true, I've not looked at the alternative boards. I saw Arduino recently put out a non-avr board too with a higher spec. Most of my experience (and gear) in this area is 15 years old.

AI is getting pretty good at writing embedded C++.
If you want higher-level language support, it's indeed a good idea to scale up the hardware.

reading regurgitated stolen C++ isn't on my TODO list of an evening either. I've been writing Go for so long now everything else feels like hard work.

I've run a color enlarger controller based on an Arduino Nano for a few years; it ran 3 color channels, timer programs for b&w and color mode and read out several encoders. This ran easily within the memory constraints of a '328P. However, given the negligible cost of far more powerful hardware (e.g. ESP32 platforms), I agree it's unnecessarily limiting to stick with the very old 328P/PB platform.

I managed to get multi-exposure and f-stop support (with test strips), into about 24kb of flash, but got dangerously close to the 2kb RAM (as in about 2032 bytes). Improving the UX and adding a G+B graded exposure option wouldn't need much more, but enough that I need to start bigger refactors. I don't think I'd get an sd/mmc driver in there either. I /think/ I could do it on a microbit, and it has enough GPIOs, but I've not had a try (need to get on and actually do some printing). The microbit actually has bluetooth support too, giving hte option of moving print profiles on with a phone app... but mobile development is definitely not on my "doing that for a hobby" list either.
I do think a Pi is probably overkill, and then you have to faff about maintaining the OS, but for less eperienced people maybe python etc are an easy route in.

 

[koraks]

regurgitated stolen C++

It's really not that, but YMMV and to each their own. I've written a decent amount of C++ over the past few years and have recently begun incorporating AI in these projects. Most software engineers today have embraced AI in some shape or form because it just speeds things up massively. The quality of the code may not be excellent right off the bat, but if you know what you're doing, you can accelerate things dramatically using AI. Previously I would spend hours writing a simple ISR using the reference manual for some chip; now I just ask AI to come up with a skeleton demonstrator for the platform involved (while feeding it the reference manual or parts thereof) and then also use it for troubleshooting. The net result is that I can get stuff done within an hour that might have taken me several days to figure out before.

Go

Yeah, that's pretty high-level. May work OK for this sort of thing, but for many things that are closer to the hardware layer, the net benefit is marginal. Again, to each their own and there are plenty of ways to skin that cat.

I do think a Pi is probably overkill

I think given the cost of hardware these days I wouldn't consider it overkill necessarily. Sure, the same thing can be crammed into tiny little STM8F003 or $0.25 CH32v003, but if you look at the bigger picture, you need to factor in the time spent on making stuff work. If you can get there with two days' work with a $75 Pi while it would take a week of cursing on a bare metal approach, it's clear that the Pi wins. Assuming it has no soul, it won't mind being bored 99.995% of the time, hah!

 

[Pegajoy]

Another option would be waiting for the Dektronics Printalyzer from Derek Konigsberg that will have a DMX512-compatible expansion port. Should be possible to connect it to a custom LED head. If I remember right from his last video, he also played with an Intrepid Enlarger Kit interface hack. There is no pricing available yet, but should be less expensive then a Heiland LED cold light head + Splitgrade Controller + LED controller unit. And you safe the effort for an Arduino or Raspi or whatever and the programming...
I am thinking about selling all my Heiland and Analyser zoo if Derek's solution keeps his promises.