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  1. #41

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    Bob I think the fact the the LED emit the same color at varying power is advantagous for color printing. I have to check but I think I can find LED that emit at the wave length where the paper material is most sensitive. I meant for the 3 layers in the emulsion. The only problem is that I don't think color analyzer would work any longer as they are designed to measure a broarder spectrum.

  2. #42

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    Checking at Kodak website for Supra Endura paper and they are most sensitive at 475, 550 and 710. At the super bright LED website you can find 470nm blue LED, 525nm Green LED and 630nm Red LED. I think they are close enough to work well. You can either pulsing the LED rapidly or control their current to selectively exposing the 3 sensitive layers.

  3. #43

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    Led's for Enlarging

    I had begun a look at enlarging AZO, in hopes of getting past the size limitation of contact printing.

    I got as far as contacting Cree Research, that makes Led's and they put me onto one of their customers, who has a "light engine" that uses 11 cree xlamps that produces 2200mw of UV. The lamps are in a six inch circle.

    If any body is interested, the vendor is

    Anthony Vilgiate,
    Infinilux, Inc
    1021 Mateo Camino
    Woodland Park, CO 80863
    email: anthony@infinilux.com
    enjoy

  4. #44

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    I opted for constant current for my led head I'm working on. I'm worried about the response of different papers at high frequency short pulses. If the frequency is not high enough fades could get actually stepped. (Consider eg. 100Hz short pulses and a faded dodge/burn).

    I'm probably going to include light level measurement for feedback (led output drops very much as it heats!). The other possibility is is to measure temperature of the heat sink and calculate indirectly the die temperature when the power level is known. The prototype will show the exact method or combination.

    Software features and calibration procedures are hard part for me because I'm including a Zonemaster type measurement (with some differences). I've desided not to make controls like "blue full, green 50%" which I'd prefer because that cannot be transfered easily from one paper to another. Working with grades (based on paper calibration!) simplifies working with different papers a lot.

    I'm suprised I've seen no RGB heads yet. I'm definately including red channel too for safe light (B&W) and color prints as well. (Oh yes, another "simple" software feature to come later on: color printing!)

    No idea yet what type of measurement/control I'll do for color but for B&W I'll measure green and blue output separately. Measuring both green and blue gives me consistence for negatives with a colored stain as well. I'll simplify measuring by pulsating channels and syncronizing measurements.

    The electronics is actually pretty simple and the features are mostly in the software. Basically all you need is an adjustable current source for led channels combined with an intelligent timer (plus input from controls and measuring probes). Being an engineer I'll just have to thow in those for everything

    Features like flashing is also easy to do with the fast turn on/off the leds have (assuming a fast current control loop). Another simple software feature to add. Based on some early prototyping I'm going for mixing chamber. Getting even light output without heavy diffusers is a real pain.

  5. #45

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    Would you share your design?

  6. #46

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    I'll consider giving more details on my project if it gets documented well enough to be published. I'm definate my project takes quite a while to get finished though.

    Basics for my project are like this: Adjustable current sources for rgb channels, a lot similar to previous schematics on this thread. Couple op amps and detector diodes for measurements. CPU has analog outputs for current sources, analog inputs for measurements. Everything else is done by software.

    My basic idea is to keep electronics very simple. Once you have a couple measurement channels (for baseboard and mixing chamber light level), know the heat sink temperature and can control the light level you're done. With those components you can create almost everything with software.

    I started with an idea of Heiland Splitgrade type controllable G/B light source including the timer. Unfortunately that can give very diffent pictures for different paper types with different responses. So, I'll include a measured table for each paper to get actual contrast on a paper independent scale. Most measuring systems seem to have reference points at just visible white and just visible black. The difference between these is the ISO R-speed which correlates well with contrast grades. B&W zones are just some steps between these two points.

    Paper manufacturers document ISO P-speed as well. However, I'm considering using the white reference point as a speed reference (to avoid adding any extra measurements). That's what one would basically do for split grade printing as well.

    The real pain is in the calibration. Software must include methods for easy calibration or the head is not that usable really. My goal is at 1% absolute repeatability which means reasonably accurate measurements and the need to do runtime correction during a long exposure as well. (Heat changes => light level changes)

    Basically I'll probably measure a base line to get a correction table depending on power level and temperature. That get's me close and the tiny correction is left for the runtime during exposure.

    I'm adding features one by one. I have a complete goal known pretty much so I can design user interface and the input/outputs for accessory harware coming later on. I'll start by using a simple guessed/measured G/B table for contrast and probably a density based RGB as well for color. That allow me to print. Then I'll add more features one at a time over a longer period.

    If anyone has good insite or references how to make a very usable color metering system I'm interested on all ideas. I'm not very familiar with color metering systems at this point.

  7. #47
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    I'll consider giving more details on my project if it gets documented well enough to be published. I'm definate my project takes quite a while to get finished though.

    Basics for my project are like this: Adjustable current sources for rgb channels, a lot similar to previous schematics on this thread. Couple op amps and detector diodes for measurements. CPU has analog outputs for current sources, analog inputs for measurements. Everything else is done by software.

    My basic idea is to keep electronics very simple. Once you have a couple measurement channels (for baseboard and mixing chamber light level), know the heat sink temperature and can control the light level you're done. With those components you can create almost everything with software.

    I started with an idea of Heiland Splitgrade type controllable G/B light source including the timer. Unfortunately that can give very diffent pictures for different paper types with different responses. So, I'll include a measured table for each paper to get actual contrast on a paper independent scale. Most measuring systems seem to have reference points at just visible white and just visible black. The difference between these is the ISO R-speed which correlates well with contrast grades. B&W zones are just some steps between these two points.

    Paper manufacturers document ISO P-speed as well. However, I'm considering using the white reference point as a speed reference (to avoid adding any extra measurements). That's what one would basically do for split grade printing as well.

    The real pain is in the calibration. Software must include methods for easy calibration or the head is not that usable really. My goal is at 1% absolute repeatability which means reasonably accurate measurements and the need to do runtime correction during a long exposure as well. (Heat changes => light level changes)

    Basically I'll probably measure a base line to get a correction table depending on power level and temperature. That get's me close and the tiny correction is left for the runtime during exposure.

    I'm adding features one by one. I have a complete goal known pretty much so I can design user interface and the input/outputs for accessory harware coming later on. I'll start by using a simple guessed/measured G/B table for contrast and probably a density based RGB as well for color. That allow me to print. Then I'll add more features one at a time over a longer period.

    If anyone has good insite or references how to make a very usable color metering system I'm interested on all ideas. I'm not very familiar with color metering systems at this point.
    Sorry, no disrespect, but I don't think you can do it; that said I don't think that if you could do it that you would give for free any information on it. If you did give it for free, it would in all probability be too complicated for anyone else to build.
    Everytime I find a film or paper that I like, they discontinue it. - Paul Strand - Aperture monograph on Strand

  8. #48

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    First a correction. Heiland Splitgrade is calibrated to papers. I incorrectly wrote it is not while I was thinking on another product that is more like a G/B VC-head.

    I've been designing this for quite some time. Checking the backgrounds and figuring out how to do these is a nasty job. Lots and lots of designing seems no progress but it will speed things up pretty soon a lot. Having checked the facts has made me feel a lot safer on the success.

    I surely undestand all the doubts. This is not the most simple project. Please be free to point out any unrealistic ideas stated so far about my design.

    I'd also point out that there are already several such products (or parts of it). Many measurement products and led heads and vc heads are out there. This will be just another. Those have and can be done. The most simple ones I know of measure just zone I and zone ix references and gets measured points (or extremes there).

    I'm sure the average Joe will not be able to replicate my "product" even with full documents and full source code/software. There will be a couple real hard circuit parts and noice protection will be essential in some part of the device. Replicating should on the other hand be simple for anyone with some expertice on this field.

    I'll give updates on my progress later on. My goal is not on a commercial product (no intrest in marketing nor finding someone with customer support to market it for me). Mechanical design makes it also not good for mass production. Units will need individual calibration as well (very bad for a commercial product but ok for a single one).

  9. #49

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    Any progress

    Harri129, have you made any progress since your last post?
    I'm designing a timer and LED head but a lot simpler than yours.
    It just mixes Green and Blue to get the filtergrades for B/W printing.

    If your interested I can send my sketch for the Arduino. It is not tested yet however.
    I would be interested in your software.

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