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Optical Phenomena with White Wine and Glass

  1. Oct 25, 2009 #1
    Hey all,

    I went to my 10 year HS reunion party last night, and took about 125 photos using my Sony Alpha 350DSLR, a kit lens, and a Promaster hot-shoe flash. The camera was set to manual exposure of 1/10th sec to allow the ambient light to fill in the background, while the flash was left on TTL (auto) to act as the primary light for the subjects, thus keeping them sharp. Focal lengths varied from 18-80mm, but generally were wide-angle. ISO was cranked up to 400 ISO to get additional fill from the ambient light. The Lens was set to max aperture of 3.5-5.6.

    The room itself wasn't very special, large chandelier type of lights which were diffused by even larger translucent coverings hung ~6 feet overhead, and they were for the most part the only source of light in the room. Even then, most of these photos were taken after those had been dimmed to the point where it became difficult to compose with the optical viewfinder from lack of light.


    When I got my images onto the PC that night, I processed all the images from RAW files using Capture One 4 by Phase One. It was then I started noticing something "unusual".


    Many of the photos exhibit some strange optical phenomena with the wine glasses. It's a rather unusually bright illumination of the wine that doesn't seem to fit the scene. There's just nowhere near that volume of light projected onto the glasses from any direction, save the flash unit itself, nor was there any gimmicky lighting within the glasses.

    The glasses were fairly standard. It was a very nice restaurant, I wouldn't be too surprised if they were crystal. The wine was white, the red wine there exhibited no such effect. Also, there's a few photos where the same glasses were filled with ice water, again with no such affect.

    The only other condition that seemed to have a role to play was how the glass was held. It seems that the wine is only illuminated if there is a hand directly behind it. IE, if the glass is held by the stem the wine does not glow. If the glass is held part-way down the area of the glass where the wine is, the part with a hand behind glows, the part above does not.


    I'm linking to a few of the photos, let me know what you think could be going on.


    Prominent effect:
    http://dansphotos.org/index.php/JHawks99/danophoto%20JHawks99%20122.jpg [Broken]

    Water, no effect:
    http://dansphotos.org/index.php/JHawks99/danophoto%20JHawks99%20106.jpg [Broken]

    There are 4 "illuminated" glasses in this image:
    http://dansphotos.org/index.php/JHawks99/danophoto%20JHawks99%20087.jpg [Broken]

    Red vs White wine:
    http://dansphotos.org/index.php/JHawks99/danophoto%20JHawks99%20066.jpg [Broken]

    This image exhibits a strong "partial illumination" effect, as the wine above where the man is holding the glass is completely transparent and un-illuminated.
    http://dansphotos.org/var/albums/JHawks99/danophoto%20JHawks99%20037.jpg [Broken]

    If anyone is interested I'd be happy to provide larger images (14.5 megapixel) that will show full detail of the effect.

    I've Googled for at least 1/2 hour, using both web and image searches and have come up completely dry.

    Thanks,
    Dan O.
    http://danophoto.net [Broken]
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Oct 25, 2009 #2
    I think that the light rays are traveling through the glass, hitting the hand, and reflecting back. If the hand is at the focus of the light behind the glass, it doesn't have to scatter back in the exact same direction it came from to be reflected back to the camera.
    Many years ago, during WW II, some airfields were lined with large corner-cube retroreflectors. Pilots would wear lamps on their foreheads (so I am told), and they could see the runway at night.
    Someone asked me if there was a way of making the reflection turn red if the pilots were off to one side. The answer was to get this red and white retroflecting tape (now available at auto supply stores), and put it at the focus of a large lens with about a 6" to 12" focal length. You will get a red or white reflection back from about 200 meters away, depending on where you are standing.
    [Added] This phenomenon is best understood by doing simple raytracing. Place a diffuse reflecting surface behind a converging lens, let the unfocused light from a distant source (infinity) hit the reflecting surface and raytrace the reflected light back through the lens. As you move the reflecting surface to the lens' focus, all the diffuse light captured by the lens will be reflected back to the source.
    Bob S
     
    Last edited: Oct 25, 2009
  4. Oct 25, 2009 #3
    Interesting. Could your answer have led to the invention of the Visual Approach Slope Indicator?
     
  5. Oct 25, 2009 #4

    Andy Resnick

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    I was thinking it was some lensing effect (the "partial illumination" image could be showing the man's (magnified) hand behind the glass, but I like Bob S's idea, also.

    One way to learn about the effect, which I agree is quite striking, is to set up some controlled lighting conditions and controlled wineglasses (with different backgrounds) and see what happens. Does it matter what angle the camera makes with the glass or light (or both)? Is it only with the flash? What is there is nothing behind the glass, or something highly scattering?
     
  6. Oct 25, 2009 #5
    I did this about 1970, and forgot about it until this post. I was unaware of VASI systems. I suspect they have slits located at the lens focal point illuminated with different color lights. A prism is better, but I won't explain why.

    The general principal is that light beams have different "emittances", which are basically the product of the spot size and the beam angular divergence. For example, a laser pen might be 1 mm by 0.1 milliradian = 0.1 mm-mrad. You can expand the laser beam to 1 cm, and reduce the divergence to 0.01 milliradian, for example, but the emittance doesn't change. If you are working at a point focus, the divergence can be large, like the wineglass situation above.
    Bob S
     
  7. Oct 25, 2009 #6
    Just thought I'd mention something that I noticed in a single image, there's one where it's not a hand that's positioned directly behind the glass, but rather a black (presumably) leather purse, with only a few studs that could possibly reflect any light at all, the hand is located well down the stem.

    http://dansphotos.org/var/albums/JHawks99/danophoto%20JHawks99%20086.jpg [Broken]

    It's one of the women on the far-left of the frame that's holding the glass.


    Is it at all possible that either the wine, the glass, or a combination there-of could be modulating the flash's light into infra-red on the reflection of the object behind it?

    I know, sounds far-fetched.

    Let me know what you think,
    Thanks,
    Dan O.
     
    Last edited by a moderator: May 4, 2017
  8. Oct 25, 2009 #7

    DaveC426913

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    That purse is in front of the wine glass. Look who's holding it.

    The reason the effect is different is because the light is travelling a lot farther behind the glass, acting like a very fat convex lens. Can't tell you what it's showing though.
     
  9. Oct 26, 2009 #8
    I believe the girl behind her should have her hand behind the glass. However, that still leaves us with the question as to why a distant hand that is not completely covering the area behind the glass would allow the glass to fully illuminate, when a hand that's directly behind the glass does not.

    Hopefully I'll have some time today to take some more shots under controlled conditions. I need to acquire some nice white wine today I suppose, should make for a fun experiment. :)

    Once I get the wine and have it all setup, what kinds of things would you guys like to see as variables? I was mostly thinking about the distance of the hand from behind the glass, as well as seeing what other surfaces are capable of recreating this type of reflective glow. (foamcor, wood, other surfaces).

    Anyone have any other ideas for things to try?

    I'll look up some info on that VASI system and try and see if I can understand better what might be behind this.


    Thanks,
    Dan O.
     
  10. Oct 26, 2009 #9
    That should not be necessary. As far as I know, the modern VASI system uses directional lights and has nothing to do with your optical effect. Sorry about the off topic post.
     
  11. Oct 26, 2009 #10

    DaveC426913

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    It won't be the materials, it'll just be white. Biggest factors are:
    - object's distance behind glass
    - size of object
    - angle of object behind glass

    I'm thinkin' that big white table or the ceiling.
     
  12. Oct 26, 2009 #11
    Hi Dan-
    The first thing to do is to shine a strong light at the wine glass (with white wine) from a long distance away, move a diffuse reflecting white surface around behind it, and determine the focus and the effective focal length of the wine glass. You can also use your hand.
    Bob S
     
  13. Oct 26, 2009 #12
    Okay, here's what doing a bit of digging has found:

    1. The effect I'm seeing on these wine glasses is very similar to the retroreflective properties of a cat's eye.

    Article on Retroreflectors:
    http://en.wikipedia.org/wiki/Retroreflector

    Image of Cat's eye acting as retroreflector:
    http://upload.wikimedia.org/wikipedia/commons/9/95/Eyeshine-BW-cat.jpg

    Now, here's where things begin to fall apart from this theory. The "cat's eye" retroreflector is created by"

    Unless, of course, you have a spherical mirror to go along with the transparent sphere, as noted above that quote in the original article. This of course is not the case here, unless a hand could ever be considered a spherical mirror.

    In the absence of the spherical mirror, you end up needing a refractive index of two times the medium, which from what I gather should be air in this case. Here's the problem:

    Water has a known refractive index of 1.333, but according to what I find here:

    http://web2.slc.qc.ca/jmc/w05/Wine/results.htm

    All of the white wines listed have a refractive index of about 1.337 to 1.338, nowhere near significant enough of a difference to cause the cats eye phenomenon IMO.

    So, where does that leave us?

    Time to get some wine!

    Dan O.
     
  14. Oct 26, 2009 #13

    Someone mentioned corner cubes... and looking at the picture remind me of a situation called total internal reflection (which is use in non-hollow corner cubes). While I am not sure if this is total internal reflection or even something evolving brewster's angle, I did think it would be benifical to try to figure out the index of refraction of red wine and white wine.

    Since you thinking about doing a experiment, I though that I should mention the below above article should gives the total index of refraction for red wine simply to confirm that it is not total internal reflection or brewster's angle.

    http://www.ajevonline.org/cgi/content/abstract/58/3/387" [Broken]

    Hope this helps
     
    Last edited by a moderator: May 4, 2017
  15. Oct 26, 2009 #14
    The problem is that when the light through the wine glass is focused on a white (or mostly white) surface that is a diffuse reflector (not a specular or retroflecting surface), the reflected light emanates from a small spot, but the divergence angle is very large. So even if the emittance (see my definition in earlier post) of the incident light is very small (e.g., laser pencil), the emittance of the reflected light is much larger due to the large divergence angle. The "acceptance" of the optical system (wine glass) for the reflected light is the spot size times the divergence of the light that will return to the original source through the lens. For a standard lens, the divergence is 0.5 times the lens diameter divided by the distance to the spot. If the bright spot is at the lens focal length, the light rays returning through the lens will be parallel.
    Bob S
     
  16. Oct 26, 2009 #15
    It's strange that you've made this connection with retro-reflectors and cat's eyes but then just considered man-made retro-reflectors.

    A cat's eye is an approximately spherical object that is filled with a liquid and surrounded on the rear surface by biological matter. I believe this is the same arrangement that, in which, you are noticing this phenomena!
     
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