Split-Grade Dodging

[kenh]

distributed:
"How did you build your reflection densitometer?"

I used an Adafruit Clue, and built a black box to hold the device at an angle to the paper to avoid the "glossy paper" from reflecting back into the device. The device has pretty much everything .. so no modifications to the Clue were needed. Just building the box and writing some software.

The clue has two white lights at the top with two light sensors placed in the middle. This creates the illumination and the light sensor. The unit has the display which makes it easy to generate the graph and see what is going on immediately without having to connect it up to a PC. It has two buttons to control the system, and three "touch" pads which I used to select menus and trigger the reading. It also has a accelerometer that I used to trigger the readings, so as I move it over the paper printed from the step tablet, it detects when I move it and triggers the reading a second later.
The device also has flash memory -- so I can change the configuration and save the state.

 

[Bill Burk]

There is a method for split grade that takes the black/deep shadow / white/specular highlight meter readings and comes up with the right blue and green exposures. Paper characterization for split grade is easy as compared to characterizing a paper for 12 contrast grades.

Inputting the meter readings for black and white points, with a few stored paper constants, should allow your head to come up with the right contrast and exposure.

http://www.darkroomautomation.com/support/appnotesgmeasured.pdf

I'd forgotten about your resource. You pretty much cover everything there thanks Nicholas

 

[albada]

Inputting the meter readings for black and white points, with a few stored paper constants, should allow your head to come up with the right contrast and exposure.
http://www.darkroomautomation.com/support/appnotesgmeasured.pdf

The second page of that document describes a simple method of determining exposure for #00 and #5 filters. The remainder of the document explains why it works, and how to adapt it to any paper. It's all based on using f-stops for both exposure and time. It's clear that Mr. Lindan put much effort into creating this method, and in designing and producing products. I bought his enlarger meter, and it has been a great help.

I suspect that he vanished for a few years out of frustration. He put much effort into improving our art, and then few people paid any attention. I'm in that situation with software: I invented a better way to design software, published a book about it (IDAR method), wrote articles, and even presented it to NASA/JPL. It's been field-tested in two products, so it's practical and not just theory. And then... nothing. People just go on their way, and ignore improvements. That's discouraging. I might be wrong, but I would guess that Lindan got discouraged by the lack of interest in his work.

I've been reading the document he wrote (linked in the quote above), and thinking about how it can adapted to LED heads. It relies on what I will call "blue dominance", which is stops-of-blue minus stops-of-green (i.e., intensity-of-grade5 minus intensity-of-grade00). My controller is based on green dominance, which is the negative of blue dominance, so they are equivalent. And his method ingeniously uses the flat portions of the curves for almost-black and almost-white, resulting in his simple method. I'm impressed. His method results in adjusting the times for blue and green in stops, but with a LED head, you can instead change the LED's power-levels and use the same time for both, gaining the convenience of having only one exposure. I'm thinking of how to incorporate his method into my controller...
Mark Overton

 

[Nicholas Lindan]

Darkroom Automation put much effort into improving our art, and then few people paid any attention. I'm in that situation with software: I invented a better way to design software ... And then... nothing. People just go on their way, and ignore improvements.

There is the old adage "No man can be a prophet in his own country," which I think also expands into "No man can be a prophet in his own time."

I also realized that another common saying needs expansion: "Invent a better mousetrap and the world will beat a path to your door and burn your house down."

It's just the way life is. You have to get used to it, so I tell myself.

 

[Nicholas Lindan]

I came across this: https://www.nytimes.com/1947/06/08/...he-technique-for-controlling-contrast-in.html
(you will need a New York Times subscription to read the whole article)

From the June 8, 1947 edition of the NYT, Section X, Page 11:

ALTHOUGH Defender's Varigam Paper, the photographic enlarging and contact paper which is printed by filtered white light to provide any desired tonal contrast, has been available for some years, the use of the Varigam filters for "dodging" purposes has been neglected...​

(Quoted without any permission whatsoever)

 

[Mal Paso]

Was Defender part of DuPont? Around 1970 I had a 250 sh box of 11x14 DW DuPont Varigam. Had the box until a few years ago.

I feel really dumb for not trying split printing earlier.

 

[Nicholas Lindan]

Dupont purchased the Defender company in the mid 40's.