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  1. #201
    Struan Gray's Avatar
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    Quote Originally Posted by Hologram View Post
    By the term volume medium I was referring to a recording medium that records the interference fringes within the depth of its layer (and be it only a 2um "thick" layer). That would be in contrast to a surface relief structure, say a photoresist. Maybe I'm wrong but I believe you could not record a Lippmann photograph as a surface relief structure.
    It could be done. With a reference beam and/or some two-photon absorbtion trickery you could generate a lateral pattern from normally incident light, but hardly worth the effort.

    Quote Originally Posted by Hologram View Post
    By the way, regarding filtered incoherent light, it's possible to make reasonably good contact copies from holograms.
    That I didn't know. I assume it is because holograms are actually quite good gratings.


    I re-read Ive's thesis last night, which is a model of clarity and concision:

    http://www.archive.org/details/anexp...tals00ivesgoog

    I also had this in my bookmarks:

    http://www.scribd.com/doc/11244006/E...er-14-Lippmann


    Both emphasise that the best and most colourful view is to be had by illuminating with collimated light and viewing in conditions which minimise diffusion, both of the illuminant, and of the light scattered by the picture. I had been led astray by modern references which assert that Lippmann plates can be, or even should be, viewed with diffuse light. Ives and Wall make much more sense for viewing colours formed by diffraction fringes.

    It also explains why viewing from the front with a mirror in place won't work. The mirror does indeed enhance the diffraction of the fringes, but specularity is reduced by scattering from the unstructured silver deposits in the part of the emulsion away from the near-mirror layer containing the lamellae. A mirror surface for viewing will only help if you could somehow remove all the non-lamellae silver.

    Wall emphasises that the mercury should be in contact with the film for as little time as possible. That mercury is a strong foggant I knew, but I wonder if it doesn't also form an amalgam with developed-out silver and destroy fringe structures.

    Ives discusses using a filtered light with the Lippmann process, and I suspect, Holmburgers, that this would be one way to improve your results. With incoherent monochromatic light the fringes are few and weak, and overlaying fringes from a whole spectrum only makes the matter worse. In a perfect world there is no reason why a pattern of silver grains in gelatin could not cope with recording a whole spectrum diffractogram, but with conventional photochemistry and the small depth of the inteference structures, there is too much mixing of the colours and you lose too much saturation.

    With a conventional scene you could expose through red, green and blue bandpass filters to get a trichome Lippmann plate. You would need filters with a narrower bandpass than the standard colour separation filters though - they essentially allow the whole spectrum through when considered together. In a studio setting you could use much narrower passband filters. Three separately-gelled flashes would give you a single exposure. If you can live with longer exposures, the easiest way of getting narrowband illumination (short of spraying laser light about) would be an LED light bank with R, G, B LEDs. Disco and DJ suppply stores have some nice bright programmable banks at very reasonable prices.

  2. #202
    holmburgers's Avatar
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    Struan, so you're suggesting taking 3 exposures with 3 filters successively? That is very interesting and completely new to me. I know that Ives did something similar, but this was with separation negatives and a screen w/ 1/3 of the surface transparent, which was shifted by thirds for the successive, filtered exposures.

    The 3 filter idea makes sense though, and I thank you for mentioning it! I have a handful of Wratten filters, one of which is "deep blue monochromat". I suspect that this kind of narrowband filter would be ideal, though the exposures would of course we epicly long.

    Very cool...
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  3. #203
    Struan Gray's Avatar
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    As I understand it, the point of the experiments with the shifting screen was to compare the brilliancy of colour when monochromatic light exposed a part of the plate all by itself, and when it was combined with other monochromatic wavelengths. Brilliancy and luminosity were OK with two colours, but dropped noticeably with three. The difference between a monochromatic source and a fairly wideband source with the same centre wavelength was dramatic.

    I (well, Ives and common sense) would suggest using a three narrow passband filters and exposing the same plate with each filter in turn. If you have three light sources (small flashes, for example) you can use the same filters on them and make a single exposure with all three lights on at once.

    You can think of the lamellae as being like a comb. If you have two combs of different spacings and hold them next to each other you can see a combined pattern of light and dark along the comb - in acoustics it would be a beat, but in visual sciences it is usually called a moiré pattern. As you add more frequencies it gets harder and harder to see the gaps, and you get more and more overlaid tines. With a continuous spectrum you end up with mostly mush. Ives has curves of the density vs. depth profile for continuous spectra, and sure enough, they are weakly modulated and not very fringe-like at all.

    Fourier theory gives you an out: you can always separate out the individual components if you have long enough combs, but the point with Lippmann emulsions is that you don't have enough depth of the lamella structures to distinguish between a large number of close wavelengths. Worse, the coherence problem, and scattering within the emulsion, mean that you can never get the required depth.

    So the answer is to use a single red, a single green and a single blue wavelength, rather than a continuous spectrum. You can do this with single wavelength sources (LEDs are cheapest and safest), or with narrow band filters on the lens and wideband illumination.

    So what if your exposure times are measured in days. It worked for Ed Weston :-)

  4. #204

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    Quote Originally Posted by Struan Gray View Post
    Both emphasise that the best and most colourful view is to be had by illuminating with collimated light and viewing in conditions which minimise diffusion, both of the illuminant, and of the light scattered by the picture. I had been led astray by modern references which assert that Lippmann plates can be, or even should be, viewed with diffuse light. Ives and Wall make much more sense for viewing colours formed by diffraction fringes.
    No way, common wisdom (and experience) still holds: you do need diffuse light for viewing a Lippmann photo. I've never done any "photos of the spectrum" though. I assume they may be different, getting even closer to a hologram.
    But a Lippmann photo of what they used to call, natural objects, absolutely requires diffuse light for reconstruction.


    Quote Originally Posted by Struan Gray View Post
    With incoherent monochromatic light the fringes are few and weak, and overlaying fringes from a whole spectrum only makes the matter worse. In a perfect world there is no reason why a pattern of silver grains in gelatin could not cope with recording a whole spectrum diffractogram, but with conventional photochemistry and the small depth of the inteference structures, there is too much mixing of the colours and you lose too much saturation.
    Definitely no easy task. But obviously, it can be done. The finest Lippmann photographs by Lippmann, the Lumière brothers, Neuhauss, Cajal and maybe others clearly demonstrate that large bandwidth spectras can be recorded into a AgX emulsion. Some of these photos are of outstanding quality and pretty bright.
    By the way, I suspect that Ives' emulsions may simply not have been good enough in respect to grain size/resolution.

  5. #205
    Photo Engineer's Avatar
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    At GEH we used normal (bright) room lights to view their Lippmann plates. They showed us a box full of them and we looked at the beautiful colors right in the open.

    PE

  6. #206
    holmburgers's Avatar
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    The Proof is in the Puddin'

    Ok, so I was able to take a better picture that really shows the color in my Lippmann plate.

    The only color is in the gas tank, and as you can see it is definitely a good representation. And actually, the digi-snap looks much less life-like than the Lippmann.

    I took this by angling a piece of glass at 45° over the plate and diffused the light from a tungsten bulb with tracing paper. In layman's terms, the key is to reflect a wide swatch of featureless light into your eyes from the plate. For instance, if you take it outside on a cloudless day, you see a reflection of a blue sky, but if you take it outside on an overcast day you will reflect back the featureless cloudy sky and this makes for the best viewing.
    Attached Thumbnails Attached Thumbnails Lippmann - Motorcycle (june 2011) holmburgers.jpg   Honda 1971 CB100 K1.jpg  
    If you are the big tree, we are the small axe

  7. #207
    holmburgers's Avatar
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    Today's Thought:

    What guide number, or how many flashbulbs, would be necessary to take an instantaneous Lippmann photograph? And would that blind you or burn your skin?
    If you are the big tree, we are the small axe

  8. #208
    holmburgers's Avatar
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    Interesting alternative to mercury reflectors?

    http://wood.phy.ulaval.ca/index.php/Reflective_Liquids

    "When properly poured on the appropriate substrate, these films show a reflectivity comparable to liquid mercury."
    If you are the big tree, we are the small axe

  9. #209

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    Damn you, holmburgers!! Some of us have work we're supposed to be doing!

    A more in-depth discussion of the reflective thin film:
    http://arxiv.org/ftp/physics/papers/0301/0301053.pdf

    Similar, but not exactly the same:
    http://en.wikipedia.org/wiki/Galinstan
    http://scitoys.com/scitoys/scitoys/t...uid_metal.html

    EDIT: Attached a copy of the paper above. No telling how long it will be accessible from that address.

    --Greg
    Attached Files

  10. #210
    holmburgers's Avatar
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    But where would APUG be without computers at work?!

    Thanks very much for finding and posting the Liquid Mirror pdf discussing MELFF's (Metal Liquid Like Films). This seems like a really interesting procedure, to say the least. Was there a date on that, or am I missing it?

    Now, I had looked at these liquid metal alloys and although they seem like great alternatives to mercury I think there are some discouraging caveats. (from wiki....)

    1 - Galinstan tends to wet and adhere to many materials, including glass, which limits its use compared to mercury.

    2 - It corrodes many other metals by dissolving them

    But, if one were to carry out a serious investigation, these would be 1st on the list to try.

    A few other ideas I had while, errr, working yesterday were (a) how about a suspension of titanium-dioxide (white powder) in glycerin? Glycerin won't wet gelatin and will stay on the surface, and although white isn't as good as a mirror like surface, it should reflect much better than simply the emulsion/air interface. The question is whether or not the titanium-dioxide or other suitable pigment would really make optical contact with the emulsion while suspended in glycerin.

    Furthermore, (b) perhaps there are metal pigments that you could suspend, and that thought led me to this -> http://www.xymara.com/xymaradesignaw...Metasheen.html

    These are vacuum-metallized aluminum pigments known by the trademark Metasheen (Ciba/BASF). I'm curious if the liquid slurry would be suitably reflective for Lippmann reflection.

    Ok, back to work...



 

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