Computer as support in the darkroom

Brings new meaning to FPU. Would that be family process unit? Filter pack underlings?

Firstly, what a bit of genius, in my opinion. Good work. Have you heard of the book "iconoclast"? Worth a read if you think like this.

Secondly, I don't see that there are accurate sensitometric measurements being fed into the database for future printing. If I would do something like this (I keep old prints with the notes written on the back of them instead of putting them in a database, although I have thought about using R for something like this), I would use a tool for accurately measuring the intensity of a few key zones on a negative, like skin, shadow and highlight. This is what I record in my notebook. There is a simple formula, which I use. In fact, when I bought a Darkroom Automation meter, I sent N Lindam a letter:

"I thought you might enjoy learning that I have found great use for this, having read a bit about HD curves and such like. I am using a colour diffusion enlarger, with only blue and green channels. I simply found the time and reading suitable for printing a Zone II shadow to the correct density and now use that reading as a custom exposure value:
log_2(t)+Meter Reading = ZoneII reading
I can therefore adjust the lens until it gets me into a similar meter ball park as I have used previously (avoiding any reciprocity issues) and then find the time by rearranging the above equation. It has literally increased my productivity 10 fold.
I am yet to make full use of the meter in terms of adjusting the balance of green and blue light to control contrast per the negative, but this will happen in due course. For the moment I am just startled at how accurate this method is in terms of getting prints out."

I have since gone on to quantify the amount of green and blue light required to hit an exact contrast setting.

Often you will meet naysayers in life. Don't be discouraged!

I like this. Appeals to my sense of tinkering. I have an RH Analyser, which is great, but I see exactly where you are coming from. Light sensor modules are available - this one I think is for arduino projects - I am out my depth here! http://www.elechouse.com/elechouse/...ucts_id=2159&zenid=j79q8v4t98s8cnafr3lt3i8ba6

It seems to me however that you have the ability to do this. The devil is going to be in the calibration, but I think you would learn a hell of a lot about printing by continuing to develop. Its a hobby after all, and we all get satisfaction out of it in our own way. I got the analyser when I started as soon as I realised that for me test strips were a time consuming PITA. With any "aid" you still have to learn how to use it - it doesn't do it all for you. I think now that I have printed for a year or so with the analyser, I have learned enough that I could quite quickly run test strips if I had to because you certainly learn the "feel" for time, contrast etc.

I am sure if you could rig up a light sensor straight in to the computer, if you took readings from a highlight and shadow you could use the information. It's how you interpret those readings into time/contrast for a particular paper. This could easily be done in a little program I'm sure. Fun project!

I like the project - but I'm biased, since I'm more or less in the same boat
I've been using various Palm Pilot models for this purpose for years - driving a relay via serial port: SEE HERE.

I intend to replace the Palm Pilot with a Raspberry Pi soon, and I find your solution would fit rather nicely
However, given that RasPi is driven by Linux, I'll have to do something similar from scratch, most likely using Python and some kind of web interface for setting the process(es) up... Most likely add a small LCD screen for RasPi (cheap car rear camera display from ebay) for visual feedback. It will be another winter project, I guess

clayne said:

Brings new meaning to FPU. Would that be family process unit? Filter pack underlings?

Click to expand...

After a while, the living FPUs got bored with their task, so they helped me in creating an automated version using Lego mindstorms. See attached Pictures.
While this was a "just for fun project" to entertain my kids, I was surprised how well it integrated with the software program and the splitgrade approach. I was not just using filters for hard and soft contrast, which got automatically selected during the final print exposure sequence. Even better was the red filter, which automatically got moved out of the way after the pre-countdown is done and the exposure starts. This helps positioning the hands for dodging before the start. I thought that the vibrations introduced by the motordrive for the filters to the enlarger column would be more of a problem than they really were. Anyhow, that was just a PoC and it was fun building it. I think if I was going to incorporate such functionality productively, I’d rather use LEDs in green, blue/UV and red to get the same thing achieved.

What I’ve done in the meantime was making prints whenever time allowed. I have now just over 200 prints in the DB, using this system exclusively. It works really well for me. I made some improvements regarding the usability in the dark. Also I’ve added a USB footswitch I got from amazon for just 9 Euro. Wouldn’t want to miss that convenience anymore. Also I hooked up a second light source (my backup enlarger set at a certain height and aperture) to the second relay on the interface card. This is controlled by a paper flashing and contact printing part of the application. Standard times for this mode are also stored in the paper database and are used depending on the paper type that is selected for the print that is worked on.

Regarding the analyser part, I went with a TSL235R sensor on an arduino, which in turn is hooked to the computer via USB. I went with the arduino approach, as this potentially could be used for a homebrewed LED head as well, because the arduino has PWM outputs I could use there.

The sensor basically gives me an irradiance reading in uW/cm^2. I use this to calculate a paper index for the highlights by making a test print. All I do at the moment is measuring the print highlight region on the easel and multiply it with the time it took to make a proper zone 7 tone of that region. This is my paper index for now. It works somewhat ok to get me in the ballpark for teststrips, which is all I wanted from this system. However as I save the paper index with all the other information in the print database (in the paper table), I think a lot of potential is wasted here. At least some contrast / filter calculation would be nice. I’m still trying to get my head around this and come up with a good approach, but probably am just too stupid to do it properly. Any hints in that direction would be greatly appreciated!

Denis, Mr Rusty and Hoojammyflip: I really appreciate your input!

I've also looked at the darkroom automation documents and this looks like a fantastic source of information.
However as I don't own their enlarging meter device, it is sometimes hard for me to follow the idea behind some of the descriptions. I think this would become clearer if I could try it out first hand at home.

I’ve now made a crude LED head modification for the Durst M605 which works quite well, even in the higher grades. I’ve used 3 RGBW LEDS from Cree http://www.cree.com/LED-Components-and-Modules/Products/XLamp/Arrays-Directional/XLamp-XML-Color I think those are the successors of the ones used in Heiland cold light head for the Focomat V35. As planned, I control them out of the application, using the PWM outputs of the same arduino that does the sensor readings.

I am a big teststrip aficionado, as I get so much information from them. So the workflow I do now basically consist of my normal steps described earlier, now using the convenience functionality of a teststrip mode for finding the base exposure and contrast:

1. I take a sensor highlight reading to get in the ballpark for base exposure (still to-do: get a sensor based indication for density range / contrast grade). To get into reasonable times, either the aperture can be adjusted, or now the overall intensity of the light source can be electronically dimmed / increased.
2. Then I make 5 teststrips, 1/3 F-stop apart around that measured highlight time to find optimal base exposure. For this, I use a contrast settings about 2,5 using the auto teststrip mode for exposure time.
3. I decide on best base exposure time.
4. I make teststrips for contrast settings using the teststrip mode for contrast variants. *
   How that mode works: I set a range of contrast (e.g. 2-4) and it sets up the number of teststrips required in ½ grade steps. (e.g. grade 2-4 would set up teststrips for grade 2, 2.5, 3, 3.5 and 4 = 5 teststrips) Contrast teststrips are always done in full exposures, as incremental teststrips are not possible here. The contrast teststrip mode automatically sets the time (the base exposure time determined in step 2 above** for all the contrast teststrips. It then automatically adjusts the contrast setting by modifying the PWM output (read: light intensity) to the blue and green leds, changing the ratio of light intensity between blue and green.
5. I carry over the evaluated base exposure and contrast setting to the “productive” print section. I then decide on initial burn and dodge sequences and make the first full print attempt.
6. I make corrections based on this print.

This is my workflow for single grade printing.
A question: Is the ratio between intensity of green vs. blue light the same ratio as the ratio for times in separate exposures would be? E.g. if the ratio for a 10 seconds exposure at a certain grade is 30% intensity blue light to 70% intensity green light. Would it be the same as the ratio between separate exposures? E.g. 3s at 100% intensity of blue light, followed by 7s 100% intensity of green light. Then the single grade to split grade conversion would be straight forward and the same system could be used e.g. for separate burn and dodge sequences for hard and soft filters.


*) I don’t use calibrated Filter equivalent numbers or paper grades yet for this step, but mainly record the raw ratio of light intensity between green and blue for now. I have some rough presets numbers though, where a certain ratio is assigned to an arbitrary “grade” setting (e.g. 50% green and 50% blue = preset 2,5). For this text I use the term “grade”, although this does not mean any standardized / speed matched paper grade. The assignment of ratios to the grade settings was done on some rough tests to give nearly even separation of grades across the spectrum for that specific paper (MG IV RC). For fine-tuning the contrast, any settings of the presets can be overridden with specific ratio settings if necessary – e.g. dial in a bit more blue and dial down green accordingly to get more contrast.
Clearly quite some calibration needs to be done for the papers I use, as the response to the ratio is dependent on the paper. I think this calibration is what systems like the Heiland splitgrade already have built in / pre-programmed in. But then again, I don’t know yet if I’ll want to go through this effort myself at all. Maybe I just stick with the intuitive approach and compensate based on experience. I have already developed some gut feeling about how much I have to compensate with the Ilford filters I currently use. I guess over time I’ll develop the same for the new material. Not very scientific – but I think that’s a good thing.

**) Maybe I’ll introduce an exposure compensation factor for the various contrast changes. Before I can do this, I have to do some more testing / calibration with the LED filtration method to find the correct factors following the method described in Way beyond monochrome. Again, probably not worth the effort for me.