DIY densitometry print timer?

Hey all,

Following a great thread on DIY densitometers, this would be a bit off topic so I’m creating a new thread.

If you’re like me, there is this annoying part of the darkroom process where you scan your negs before printing, where I tell myself I’m avoiding wasting paper on a frame with just enough camera shake you couldn’t see it on a contact sheet. Personally, I DSLR scan them. Then, they after the effort of grading them in NLP, I rarely wet print them.

The feature I'd like to develop is for the software can provide me a set of starting points of times and grades to print. Further refinement could be possible for split grade printing, dodging and burning, etc. All the user need provide is as a user, provide a calibrated step wedge print strips (I use a real densitometer, but I contend a digital camera would work too).

The result could be darkroom users eliminate the need for contact sheets (I hate them), print steps, which saves expensive paper and a lot of time.

Thoughts?

peoplemerge said:

The feature I'd like to develop is for the software can provide me a set of starting points of times and grades to print. Further refinement could be possible for split grade printing, dodging and burning, etc. All the user need provide is as a user, provide a calibrated step wedge print strips (I use a real densitometer, but I contend a digital camera would work too).
The result could be darkroom users eliminate the need for contact sheets (I hate them), print steps, which saves expensive paper and a lot of time.

Click to expand...

Could you describe in more detail what you have in mind?
For example, "is for the software can provide" sounds like you want some software. But the title sounds like hardware.
And "provide a calibrated step wedge print strips". How will a step-wedge strip help me print my negative correctly?
More detail is needed.

I scan my 35mm negs only because they're just too tiny to see what's really there, even w/ a loupe. A straight scan w/o editing is simply my version of a small proof print.

Derek Konigsberg (dkonigs here on Photrio), who created the Printalyzer Densitometer (I bought one, and love it), has an analyser/timer project in the works that's probably pretty close to what you want. See https://www.dektronics.com/ for more info.

Commercial options may be found at https://rhdesigns.co.uk/ and http://www.darkroomautomation.com/da-main.htm - I have the Analyser Pro, from RH Designs, and am very happy with it. I'm pretty sure I'll still buy the Dektronics Printalyzer when it becomes available, though, for the added features and the open source firmware.

The contact sheet that you hate:
(a) does not take that long
(b) preserves some useful information: the relative density and contrast between frames
The relative density is lost by the scanning auto-exposure; furthermore, when using a dedicated scanner in the standard way, with white and black points fixed at x% of the histogram, the contrast information is also lost --normalized to a standard value.
See this thread with a closely related topic:

peoplemerge said:

The result could be darkroom users eliminate the need for contact sheets (I hate them), print steps, which saves expensive paper and a lot of time.

Thoughts?

Click to expand...

You don't need contacts sheets if you have a loupe and a light table. Have not made a contact sheet since the early 1980s.

Like ic-racer, I don't make contact sheets. After a while you get used to reading the negatives either in the raw or by judging the light transmission when you put them in the enlarger.

I’m a software engineer in my day job, and was thinking of digging into scan metadata used by NLP / Lightroom. I’ll need to do some diligence there.

It’s nice to see people like @dkonigs making densitometers. (Thx @tih ). The rhdesigns one seems to do most of what I have in mind. Dang, expensive, tho!

I have and use a beautiful vintage densitometer for film testing, in addition to a color analyzer which is pretty good at starting densities. I usually do some step wedges even using the color analyzer, but maybe I just need more practice … or knowledge.

Thanks @Bernard, auto exposure could be an issue. I’m wondering if the EXIF metadata contains a scanner brightness level to get an estimation.

I don’t do contact sheets for other reasons: when I do print roll film, I use an enlarger with a film advance dial to product first straight prints, so I prefer to not cut film then, if ever.

In my NLP workflow, the software helps guess starting exposure and contrast using fb+f values and dmax. I normally set exposure on the first frame and repeat it for the whole roll, which makes the post process quicker. If I go to wet print, I’ve got to repeat that analysis by hand. Wouldn’t it be dandy if the software even tried to help?

peoplemerge said:

In my NLP workflow, the software helps guess starting exposure and contrast using fb+f values and dmax. I normally set exposure on the first frame and repeat it for the whole roll, which makes the post process quicker. If I go to wet print, I’ve got to repeat that analysis by hand. Wouldn’t it be dandy if the software even tried to help?

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I think it's a great idea. You can create a computational model of paper exposure and contrast. There are a few different approaches you can take. There are standards and research papers available on the topic, going back to the 1930s, and I would suggest that you start there. There are also a couple of good modern sources, including Phil Davis' Beyond the Zone System (incl. Win Plotter, a MS Windows app), and Lambrecht and Woodhouse's Way Beyond Monochrome. And, of course, Photrio is full of amazing resources and very knowledgeable people.

I have written such a program myself and will probably offer it to the community, once its GUI is complete. I use it to calculate all of the needed parameters involved the printing process, including test strips, burning, dodging, etc. It helps me test papers and it automates my workflow. My program generates an XSLT document with companion data tables and graphs. I also make a set of "chips," actual paper tone samples, to go along with the software.

But the question is whether it's necessary, and my opinion is that it absolutely is not necessary to have software help one figure out how to make a fine print. Having said that, the process of writing the software, researching the topic, reading the research papers, etc. has taught me more about printing than I otherwise would have learned. But that's just me. Everybody is different. Good luck!

peoplemerge said:

I have and use a beautiful vintage densitometer for film testing, in addition to a color analyzer which is pretty good at starting densities. I usually do some step wedges even using the color analyzer, but maybe I just need more practice … or knowledge.

Click to expand...

What kind of color analyzer do you use?
I used to use (briefly) a few LiCi ColorStar analyzers. When used on their spot-measurement setting, it was possible to (1) read negative density range, i.e. determine required printing grade and (2) calibrate the analyzer for the speed of the paper used. Combined, it would do precisely what you want. I never bothered to spend much time on #2 because you'd have to dial in the calibration for every paper you use, and I happen to use lots of papers side by side. If you standardize on one or two papers, it would be a fairly convenient approach.