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  1. #191
    holmburgers's Avatar
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    Lippmann

    Here are several views of my 1st Lippmann plate, or at least an attempt at it. It's from the same batch of plates that R Shaffer used and by the way Rob, did we ever figure out what the actual emulsion was? I seem to recall that the lady from Laser Reflections gave us something different than Slavich PFG-03C, which is what we originally inquired about.

    It was developed with GP-2 in the A+B manner described earlier and advised by Darran Green.

    It was soaked in a 10% solution of chrome alum for 10 minutes, 3 minutes in the developer, an 8ish minute wash & a couple minutes soak in a 2% glycerin solution.

    My solutions were probably too warm, at 20-21°C, whereas 18.3° (65°F) is recommended. Next time I'll cool them down.

    To be honest, none of these pictures show any interference color effect. I believe the plate was generally underexposed and the subject is quite far away. Next time, I'll choose a bolder composition that compliments the small format.

    Yes, that's me sitting next to a motorcycle.. I enjoyed trying to sit still for the 6 minute (f/11) exposure, but pesky mosquitoes started biting me at about 3 minutes and at that point I resigned to being a blur in the final image.

    The only point where I can see interference colors that resemble reality are in the gas tank, which is Honda's lovely 1971 Candy Gold. There is a distinct gold hue at this point, and it stands to reason as the gas tank was perhaps the only point in the scene receiving full sunlight & exposure (it's quite reflective as well).

    I chose a particularly dicey lighting situation (contrasty), sitting under the patchy shade of a hedge tree in early evening.

    The strange brown hue visible in one of the pictures is the emulsion side, the same side that in the other pictures looks like a beautiful mirror. Very strange. You can also see evidence of the border where the plate was resting on the mat-board frame. I'm wondering if my "light sink" fabric is doing a good enough job..

    The holder was very easy to make, and fun.. but just don't make it until you've measured your plates...! An easy way to do this in the dark is to mark the edges of the plate(s) with a pencil on paper. I ripped out the center divider of a normal double sided cut-film holder and glued the fabric and mat-board frame to the backside of the other darkslide.
    Attached Thumbnails Attached Thumbnails APUG - Emulsion Side (reflection).jpg   APUG - Emulsion Side (focus).jpg   APUG - Glass Side.jpg   APUG - Glass Side 2.jpg   APUG - Glass Side Transmission 2.jpg  

    APUG - Emulsion Side 2.jpg   APUG - Plate Holder 1.jpg   APUG - Plate Holder 2.jpg   APUG - Plate Holder 3.jpg  
    Last edited by holmburgers; 06-23-2011 at 12:17 AM. Click to view previous post history.
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  2. #192

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    Quote Originally Posted by holmburgers View Post
    Here's a theoretical proposition... is there another liquid that would be easier to work with than mercury and more reflective than no mirror whatsoever?

    The only thing that comes to my mind are the metals pointed to in the IBM's US 4054453 - mainly gallium that is.

    Quote Originally Posted by holmburgers View Post
    For instance, would there be an advantage in using water as opposed to no reflector at all. In the reflector-less, Bjelkhagen method (we'll call it), the reflection comes from the emulsion-air interface, correct?
    Yes. For the history records, the "Bjelkhagen method" has been invented by Hermann Krone(1894).
    I assume water won't work in this case because the index difference at the emulsion/water interface will be too small. If you want to dig further, I think the whole thing relates to Snell's law (see http://en.wikipedia.org/wiki/Snell%27s_law).

  3. #193

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    Quote Originally Posted by holmburgers View Post
    Here are several views of my 1st Lippmann plate, or at least an attempt at it. It's from the same batch of plates that R Shaffer used and by the way Rob, did we ever figure out what the actual emulsion
    Good on ya Chris for giving it a go.

    We have the GEO-3 plates.

    IMO you've got a couple places you could try adjusting

    I made my plate in bright mid-day sun 2min @ f/8 and that seemed a bit overexposed. But it was even illumination. So your possibly underexposed.

    Gotta get your temps down and keep them reasonably consistent from bath to bath.

    Other than that, looking forward to seeing your next try.

  4. #194
    holmburgers's Avatar
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    Thanks Rob. Yes, it's about time I gave it a go.

    The answer seems fairly self explanatory, but I'll ask anyways... why such low temps? Is that pretty standard for holographic materials?

    As for the exposure, the white paint on my gas tank is that dark, solarized, blue color, while the gold paint gets the interference colors. So I'm both over & under it seems, but generally it was tough light to shoot in, and I knew that going into it.

    I'm also looking forward to giving it another go, and sooner this time. The whole procedure was pretty easy, and I spent more time mixing the chems than shooting & processing.

    Gallium seems very interesting. It looks as though it was first made in 1875, so it definitely stands to reason that Lippmann might not have known about it, or enough quantity didn't exist on the face of the earth at the time! Surely mercury would've been easily available and cheap.

    Any idea what kind of quantity one would need, theoretically? It's density is 6.1 g/cm³. 100 grams will cost you $170 from one supplier, but undoubtedly there are deals out there. Very intriguing...

    Thanks for the word on Hermann Krone.
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  5. #195
    Mustafa Umut Sarac's Avatar
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    Chris , all laser experiments , interferometry done at where the air fluctations are low. So may be they do all these experiments at cold weathering because air come to ground.

  6. #196

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    Perhaps because we want to alter the gelatin as little as possible and warm solutions may swell the emulsion. In my case, mostly because the instructions I was following indicated 65deg max.

  7. #197
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    The melting point of unhardened gelatin is approximately 68 deg F. Above that temperature, it will melt and dissolve in the processing solutions.

    PE

  8. #198
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    Back from midsummer. It was fun.

    I don't want to speculate too much on whether or how a reflector improves the viewing of Lippmann plates. I haven't made or viewed them, and it seems impertinent to lecture to those of you who have. Kudos for giving this a go.

    However, basic physics can help to understand why some things work and others do not. For example, if you want a strong reflection at the surface of the emulsion you need to provide a sharp mismatch in the refractive index.

    Metals do this for free. This isn't the place to learn about refractive indices in metals, but in short, for light below a certain frequency, usually in the UV, metals have zero or very low real refractive indices. That means the refractive index difference is similar to the refractive index of gelatin, around 1.5.

    Transparent materials like glass and air mostly have refractive indices between 1 and 2. To get an index mismatch as large as that between gelatin and a metal you would need to get up to 3 or more, and even diamond is only 2.5. The highest index oils for immersion microscopy are around 1.8-1.9. There are materials with higher indices, such as most semiconductors, but they absorb too much to be useful as mirrors. Basically, any non-metallic reflector is going to give you a much weaker reflection.

    One reason the interference in a Lippmann plate is weak is that your light is incoherent. A laser can fill a thick emulsion with fringes, but incoherent light does much worse, even if it is filtered to be monochromatic. A rough rule of thumb for thermal light (black body radiation, aka sunlight) is that the coherence length is of the order of the centre wavelength. In layman's terms that means you can only expect to get two or three fringes. It's one reason why Lippmann emulsions are thin: there is no benefit to a thicker emulsion, it just wastes silver and absorbs and scatters light.

    You can probably maximise your chances of getting good fringes by reducing the range of angles at which the light strikes the emulsion. Smaller f-numbers are the easiest way to do this, but retrofocus or more exotic telecentric designs will help too.

    FWIW, the Morpho butterfly scales are 3D on the nanoscale. The remarkable thing about the Morphos is not that they have lovely colours, but that their colour is so strong, and so pure, over a wide range of angles and lighting conditions. If you could somehow reproduce their method of generating colour, and vary it across a substrate, you would be a very happy camper indeed.

  9. #199
    holmburgers's Avatar
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    The problem with the reflector, and the thing that didn't occur to me until I had a go at it, is that you view the interference colors by looking at the emulsion side. In the film holder, the light passes through the glass substrate to the emulsion and into blank space where it is ideally not reflected back by the velvet, and interference arises from the RI difference between gelatin & air (2 & 1.5, right?)

    So, for a reflector to work in the way you describe, it would have to "disappear" and "re-appear"; switching its position in relation to the emulsion.

    Interesting about coherence and use of higher f/stop. That would be an interesting thing to test out, and fairly easy. I don't know if we can tolerate much more of an increase in exposure times though..

    Actually, I think the long exposures are one of the most enjoyable things about this kind of photography.

    Herbert E. Ives did an investigation on Lippmann photographs while at Cornell (I believe) and utilized a technique pioneered by Cajal. This technique involved swelling the material so that the fringes were brought into the reach of microscopic investigation. He discovered that the fringes only went so deep, but determined that this was due to the sensitizing method, which had been by bathing the plate in dye solutions. So, Ives incorporated the dyes into the emulsion and was apparently able to get much deeper fringes and better color.

    He also made 3-color images with Lippmann plates, but that's a tale for another time...
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  10. #200

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    Quote Originally Posted by Struan Gray View Post
    One reason the interference in a Lippmann plate is weak is that your light is incoherent. A laser can fill a thick emulsion with fringes, but incoherent light does much worse, even if it is filtered to be monochromatic. A rough rule of thumb for thermal light (black body radiation, aka sunlight) is that the coherence length is of the order of the centre wavelength. In layman's terms that means you can only expect to get two or three fringes. It's one reason why Lippmann emulsions are thin: there is no benefit to a thicker emulsion, it just wastes silver and absorbs and scatters light.
    I agree. By "volume recording medium" I didn't advocate using "thick" recording layers for Lippmann photographs. That's why commercial holographic AgX emulsions, which usually are around 8um thick, are certainly not the best solution for Lippmann work. On the other hand, these materials have been greatly improved. Scatter becomes very negligible with grain sizes <10nm - even for blue and violet radiation.

    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.

    By the way, regarding filtered incoherent light, it's possible to make reasonably good contact copies from holograms.


    Quote Originally Posted by Struan Gray View Post
    FWIW, the Morpho butterfly scales are 3D on the nanoscale. The remarkable thing about the Morphos is not that they have lovely colours, but that their colour is so strong, and so pure, over a wide range of angles and lighting conditions. If you could somehow reproduce their method of generating colour, and vary it across a substrate, you would be a very happy camper indeed.

    Yes, they're truly amazing. See: http://www.opticsinfobase.org/oe/abs...?URI=oe-5-4-87



 

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