The Diffraction Process of Colour Photography - Prof. R.W. Wood, 1900

Discussion in 'Alternative Processes' started by holmburgers, Jan 14, 2011.

  1. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    The iridescence found in soap bubbles, crow's feathers, CD's, oil slicks, butterfly wings and countless other places is created by diffraction.

    Diffraction is nature's digital; in much the same way that a series of 1's and 0's make up digital information, diffraction relies on a sort of ON and OFF system to create any colour of the spectrum.

    In classical physics, the diffraction phenomenon is described as the apparent bending of waves around small obstacles and the spreading out of waves past small openings.

    If said "small obstacles" & "small openings" are arranged in a constant & repeating manner, only certain waves will "make it out alive" upon passing through a diffraction grating, thus we will see a specific, predominating colour.

    This of course is the modus operandi of the Lippmann color photograph. But there is another method in which to produce colour photographs by diffraction, invented by Professor R.W. Wood of the University of Wisconsin. The most complete account of this procedure can be found in A Handbook of Photography in Colours by Thomas Bolas, Alexander A. K. Tallent, Edgar Senior; published in 1900 by Marion & Co.

    It begins on page 290; luckily it is on Google books -> http://books.google.com/books?id=1J... senior handbook&pg=PA290#v=onepage&q&f=false

    In short; you have 3 ruled line screens, or gratings printed on transparent film. The gratings have lines that are 2000, 2400 and 2750 to the inch. These are the "masters" to create the diffraction gratings.

    The novel part of the process is in these screens, which will be printed onto dichromated gelatin (DCG). With these fine lines impressed into the gelatin, a diffraction grating is created; meaning that light will go thru it, scatter, and depending on the viewing angle you will see different colours. Each of the 3 screens is capable of creating all colours, but not from the same angle of view. By distributing the lines differently in each screen, red, green & blue are created simultaneously from each respective screen if viewed from a specific angle.

    Confused? Keep reading...

    As usual with 3 color work, you have 3 separation negatives of the subject, taken thru the standard separation filters. The negatives must be made into positives however, and each one is then placed in contact with the appropriate line screen, red w/ 2000 lpi, green w/ 2400 lpi and blue w/ 2750 lpi. These are then contact printed onto unpigmented dichromated gelatin.

    Just as in the gum or carbon process, the DCG is then developed by etching with hot water to dissolve the unhardened gel. You are now left with 3 clear images. Due to the extremely fine lines courtesy of the line screens, these DCG plates are now diffraction gratings with diffraction "zones" relating to the separation positives which they were printed in tandem with.

    Imagine a b&w separation positive of a red apple on a black background. The apple will be very transparent, surrounded by heavy density. Therefore, the clear portion will let thru the line screen and a diffraction grating corresponding to red will be made in relation to the apple.

    This is the basis of the process. The only trick being that it requires a simple viewing apparatus; though I think that it basically just limits your viewing angle to a small degree, which could be achieved with a steady hand, or at most a piece of carboard with a hole in it.

    The result is pure, permanent colour photographs!

    I've attached a Word DOC with all figures and text from the book. I did the OCR from the Google books version.

    Enjoy!
     

    Attached Files:

  2. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    edit: technically speaking, oil & soap would be examples of thin-film interference, not diffraction. Forgive me...
     
  3. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    So, I'd just like to reiterate how (relatively) easy this process would be for someone who already does carbon or other dichromated colloid processes. The result is a color picture that relies on diffraction, and thus cannot fade.

    Quote, "The colours are extremely brilliant, and there is a peculiar fascination in the pictures, since, if the viewing apparatus be slowly turned so that its direction with reference to the light varies, the colours change in a most delightful manner, giving us, for example, green roses with red leaves, or blue roses with purple leaves, a feature which should appeal to the impressionists."
     
  4. DarkroomExperimente

    DarkroomExperimente Member

    Messages:
    596
    Joined:
    Nov 23, 2007
    Location:
    Washington D
    Shooter:
    Multi Format
    isn't this how the polachrome film worked? ...or was that something different
     
  5. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    No, this system was definitely never used commercially. Very much a "lab curiousity". For one thing, the viewing angle has to be very specific for correct color, hence the need for a specialized viewer. All the viewer does is confine the angle of view however.

    I believe Polachrome worked off the screen-plate principle.
     
  6. Joe VanCleave

    Joe VanCleave Member

    Messages:
    609
    Joined:
    Jan 20, 2004
    Location:
    Albuquerque,
    Shooter:
    Pinhole
    I disagree with the OP's inference that the diffraction effect is "digital" because it produces discrete, light and dark, positively and negatively reinforced interference patterns.

    Assuming it were true, such a whole number unity effect would not be properly termed"digital" but rather an artifact of Boolean logic. It would be "Boolean," not "digital".

    But of course, the diffraction of photons is a wave-like phenomenon, governed not by Boolean principles at all, and is most decidedly "analog" in nature, in the sense that multiple waves interfering with one another out of phase produce additive and subtractive vectors whose output space might resemble some discrete function only superficially, absent a deeper understanding of the underlying principles.

    ~Joe
     
  7. Lionel1972

    Lionel1972 Member

    Messages:
    207
    Joined:
    Oct 21, 2009
    Location:
    France
    Shooter:
    4x5 Format
    Thanks Chris for digging out again another forgotten amazing color photography process!
     
  8. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    Joe, I feel that you're failing to see my statement as an analogy. But I do agree with you that it's not a very good analogy. I think that this statement...

    the diffraction of photons is a wave-like phenomenon, governed not by Boolean principles at all, and is most decidedly "analog" in nature, in the sense that multiple waves interfering with one another out of phase produce additive and subtractive vectors whose output space might resemble some discrete function only superficially

    ....eloquently describes the principle. That is of course, after I looked up some of the terms.

    Thanks Lionel, my pleasure!
     
  9. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    Hey all.

    So I'm curious about how one would make the "line gratings" that are 2000, 2400 & 2750 lines to the inch. That's beyond the scope of a lens+film or a conventional printer if I'm not mistaken.

    Professor Wood's gratings were made by Cornell's Dividing Engine, which I guess is basically a machine that is used to cut divisions in instruments like rulers, sextants, the like.
     
  10. gmikol

    gmikol Member

    Messages:
    304
    Joined:
    Mar 2, 2009
    Location:
    Vancouver, W
    Shooter:
    35mm
    Just as an example, 2540 lines per inch (really, line pairs), is 100 lp/mm.

    This is certainly within the realm of high-resolution document/copy/litho film and lenses, so currently-available materials would be able to support the line gratings. In fact, in the text, the author states "photographic copies of these (gratings) were used for the experimental work."

    As for creating gratings of the required frequency, this is more difficult. Commercially, you'd want to look for custom "Ronchi Rulings", but these are not inexpensive ($1000 per grating for 4x4" chrome-on-glass at Edmund).

    A crazy idea I've had floating around in my head for a while would be to get 600- or 900- line-pairs per inch films on a 3600 DPI imagesetter (3-dots black/3-clear or 2-black/2-clear, respectively, or maybe 2-black/3-clear to account for dot gain [720 lp/in]), which you could then make reasonable-ratio reductions (in the range of 2x to 5x, depending on what your imagesetter films are) using a 4x5 camera or enlarger onto litho film. If you're using a white light source, best to use an APO enlarging lens. Can't guarantee the quality you'd get, but I can't see any other way to get there.

    --Greg
     
  11. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    Ahh! Greg, of course, you're absolutely right. I'm not sure what I was thinking regarding the LPI (actually I do know what I was thinking, but I'm embarassed to admit it!)

    The Ronchi Ruling is perfect for sure... check please. :D

    What about one of those "ink-squirting desktop enlargers", are they capapble of that? I'll do some checking
     
  12. gmikol

    gmikol Member

    Messages:
    304
    Joined:
    Mar 2, 2009
    Location:
    Vancouver, W
    Shooter:
    35mm
    I don't think so...I've played around with it a bit about a year ago, and for line-screens like this, the best I was able to get was about 540 dpi (270 lp/in). I've heard of a few new tricks since then that I'd like to try, but I don't have that printer anymore.

    --Greg
     
  13. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    How much do you think the image-setter service would run? That might be the best option.

    Another thing I've wondered about is the mathematical relationship between the gratings (2000, 2400, 2750) and how those relate to the primary color wavelengths. It might be painfully obvious, but I can't see it.

    I think there's a lot of creative potential for this kind of "print". Imagine having a large image made in this way, and mounted as a window high in a room with vaulted ceilings, for instance. By moving about the room, the image would shift through a menagerie of colors and only at one specific location would the proper colors pop into being. I think that could be really fantastic.
     
  14. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    Last edited by a moderator: Jun 10, 2011
  15. gmikol

    gmikol Member

    Messages:
    304
    Joined:
    Mar 2, 2009
    Location:
    Vancouver, W
    Shooter:
    35mm
    Well, if you crunch the numbers, you get the following:

    2000 lp/in = 78.74 lp/mm = 6.35 um (micron) line or space
    2400 lp/in = 94.48 lp/mm = 5.29 um line or space
    2750 lp/in = 108.3 lp/mm = 4.61 um line or space

    Looking at those numbers, they are about 10x the wavelength of what might be considered red, green and blue light, respectively (though the blue seems a little long to me). I would guess it has something to do with the power of the viewing lens and the angular offset that is desired/needed. I would further guess that other combinations of viewing angles and lenses might benefit from different line screens.

    I'm very definitely not an optics person, so maybe someone else can explain further, 'cause I'm at my limits, here.

    BTW--First link in post #14 requires membership.

    --Greg
     
  16. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    Ah, thanks for doing those numbers Greg. That makes sense, but I couldn't figure out how to get there. The blue does seem a tad long, but must be ok -> http://en.wikipedia.org/wiki/File:Linear_visible_spectrum.svg

    Sorry, yeah I don't have a subscription to that either, but I found it on Google books via that citation -> http://books.google.com/books?id=Tr...&resnum=1&ved=0CCoQ6AEwAA#v=onepage&q&f=false (type in page 339)

    I actually haven't read it yet, so I'm not sure what the improvement is. Unfortunately, the google books scan has cut off the bottom of each page, so I don't know how coherent it's going to be.
     
  17. gmikol

    gmikol Member

    Messages:
    304
    Joined:
    Mar 2, 2009
    Location:
    Vancouver, W
    Shooter:
    35mm
    I just realized I left you hanging on this...

    Assuming you want to make 4x5" images...

    2750 lp/in (@ 4x5") --> ?? @ 600 lp/in (imagesetter film)
    2750/600 = 4.583x reduction

    4*4.583 = 18.333"
    5*4.583 = 22.9"

    Looking at the on-line price list of a service bureau in my area, they charge:

    19 x 25 $48.75
    20 x 26 $54.50
    22 x 28 $63.25

    Hope that helps.

    --Greg
     
  18. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    Hey Greg,

    That fact that you don't treat a question like that as rhetorical is a testimony to your character. :D

    OK, I think I fully understand what you're proposing now. You'd get just one of these films, and use it as a master to make smaller line rulings on a high-contrast film.

    A short aside; so I found a biography of Herbert Ives and the above mentioned "Improvements in Diffraction Color Photography" [sic] was one of his graduate papers while at Cornell, IIRC. Same with a similar paper on Lippmann photography by him. I love imagining the period when stuff like this was cutting edge; being studied at institutes of higher learning. I guess that Professor Wood himself was the authority on color at the time, according to the biography I read.
     
  19. gmikol

    gmikol Member

    Messages:
    304
    Joined:
    Mar 2, 2009
    Location:
    Vancouver, W
    Shooter:
    35mm
    Right...exactly...a single master, generated at the native resolution of the imagesetter (600 lp/in works well for 2400 and 3600 dpi imagesetters). 3 different reproduction scales to get your rulings for imaging. BTW--Some can also image directly onto RC paper...it should support that resolution. And you have a reflective master to work with, instead of having to rig up a big backlight.

    If you end up going down this road, make sure the service bureau really understands what you're looking for in terms of output. It's probably way outside their realm of experience, unless they've done other weird stuff for alt-process people before.

    --Greg
     
    Last edited by a moderator: Jun 14, 2011
  20. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    I like the idea of getting it on RC paper. I was already trying to figure out how the heck I'd back-light that...

    Bob Carnie might be someone to consult on this issue.

    Even though I can't possibly say that I'll be doing this tomorrow, or next week, or even this year!, it's on my list of things to do for sure. I do think that you've proposed the best route to do it.
     
  21. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    ...and...
    Revisiting this all-too-excellent idea today and have a few thoughts. So with a 600 lp/in screen of parallel lines printed on an ≈18.5"x23" paper, I have a master from which I can reproduce onto 4x5" film the appropriate line screens; 2750 lp/", 2400 lp/" and 2000 lp/". Furthermore, this master would allow one to make any frequency line screen, as needed, by simply changing the distance from which you are photographing it (the magnification factor).

    My question is, what kind of lens is capable of doing this, and what kind of film? Would your typical process lens handle this? As for film, what about Arista Ortho Litho?
     
  22. Struan Gray

    Struan Gray Member

    Messages:
    914
    Joined:
    Nov 5, 2004
    Location:
    Lund, Sweden
    Shooter:
    Multi Format
    The heart of the matter: any lens capable of reproducing these gratings has to resolve clearly at least 100 lp/mm, and over a 4x5" field at that. Such lenses exist, but they're not cheap.

    There is a huge support and service industry supplying chip-makers with photolithography tools and chemicals. One part of this is makers and suppliers of the 'masks' used to define the patterns which are then projected onto a photosensitive resist with the hugely expensive lenses I just mentioned. These masks are usually chrome on glass (or quartz) and are tough enough to be used for contact printing as well as projection printing.

    One standard size is 5" square, which will have a large enough patterned area to contact print onto 4x5 film. Masks are specified according to the size and precision of the line features, and you pay for every step in quality, but your needs are at the low end of what is regular production, and you should be able to get masks made for a reasonable price. I used to typically pay €100 for this size and quality for one-off patterns, but I did the pattern design myself. You may be able to get a local university department to help you out (mask-making is also sometimes a routine service at high-tech incubator parks for startups) and pull the cost down further, or just help with design and ordering so that you avoid re-makes.

    Such a mask would work well as a master, which could be contact printed onto lith film to make working gratings for print production.

    I calculate that Wood's rulings produce coloured light at around 72-73° off axis. The viewer in the article you posted would either need to include a hefty wedge in the lens in front of the image, or have the peephole way off to the side, or (more likely) illuminate the image with collimated light coming in from the back at 72-73° off axis. The sun will work well if placed at the right angle, but a projected beam might be more reliable, especially in Rochester winters.
     
  23. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    Struan, I apologize for not responding sooner to your excellent post here.

    The photolithographic masks you're talking about sound like a reasonable alternative to say Ronchi rulings and the like. I need to send some emails and find out what the manufacturers think of this application.

    I wonder if there's not some way to make our own rulings cheaper and easier... Is it possible, for instance, to create line patterns with holography, or some kind of interference pattern? DCG is certainly capable of the resolution, but where does our image source come from?

    I do like your idea of getting together with a university though, or perhaps it's possible that someone would be willing to "lend" their rulings for the purpose of contact copying.

    I'm very curious to know how you calculated the viewing angle. Pray tell! :smile:

    On a different note... I'm wondering if one could make a reflective version of diffraction photography. For example, what about etching onto a sheet of metal? Or, I guess, is it possible that these glass versions could be viewed via both transmission and reflection? Actually, when I think about a diffraction grating I recently handled, it was impossible to see the color by looking at the film; it had to be "projected". Hmmm... the physics is beyond me i'm afraid.
     
  24. CMB

    CMB Subscriber

    Messages:
    94
    Joined:
    Mar 17, 2011
    Location:
    Santa Cruz,
    Shooter:
    Multi Format
    Woods interference screens/diffraction gratings are similar to the "pellicles" used in one-shot cameras. The Devin-McGraw pellicles were made by pouring gelatin onto a ronchi grating (chrome on glass plate) and then stripped off when set. It would seem that an etched metal plate, as you suggest, would work as well.


    BTW: The Frontispiece of A Handbook of Photography in Colours was the first published "natural" color photograph.
     
  25. holmburgers

    holmburgers Member

    Messages:
    4,425
    Joined:
    Aug 13, 2009
    Location:
    Rochester NY
    Shooter:
    Multi Format
    Well that certainly does bode well for this idea. Utilizing structural colors is the most permanent kind of color we can make. In fact, fossils of beetles can still be quite colorful even after millions of years in the ground. UltraStable is good.. but this kind of color is epoch.

    (pun intended... :laugh:)

    That frontispiece you mention can be seen here... http://archive.org/details/cu31924031248119

    My university library has an original copy of this book and it's one that really got me into this early color stuff. A very interesting read for sure. Cutting edge color photography at the turn of the century, before they had it all figured out.

    Thanks for your comment!