PetaPixel

Photo of Laser Pointer Through Rain Reveals Water Drop “Snowflakes”

On a rainy day recently, light painting photographer Jeremy Jackson was playing around with a green laser pointer when he discovered something interesting: all the out of focus raindrops in the photograph had a lined pattern in them — and each one was unique! These “water drop snowflakes” were found in all of the photos he took that day.

Anyone know what causes this phenomenon?

(via DIYPhotography)


Image credit: Photograph by Jeremy Jackson and used with permission


 
  • http://clintmckoy.com CM

    The designer, God.

  • Anonymous

    Uhm… a polarizing filter? That’s the my first, off the top of my head, guess.

  • http://twitter.com/_KidIncredible Chuck D

    I’d imagine that all of the rain drops are microsopically different in shape and size. Add in the super short wavelength of the laser light and there’s probably enough variation in the light refraction from each drop to look unique or different.

    Or I just made up some pseudo-physics that sounds convincing.

  • http://twitter.com/TrancedAnts -H.

    The snow in Spain stays mainly in the rain. :o)

  • http://twitter.com/ctownson Curtis Townson

    Maybe they’re acting as tiny magnifying glasses and the patterns you’re seeing are just the inside of the laser pointer?

  • Kswanson88

    well that actually does sound pretty convincing, at least to me.

  • Mario Amaya

    Yes, I do know. :-) The answer lies in the diffraction of light waves. They occur all the time, but only with lasers we see them because laser radiation is coherent – all the waves have nearly the same wavelenghth, are collimated (parallel in direction) and are in near perfect phase as they exit the laser generator. Once the waves hit an obstacle, they scatter in different directions, forming these interference patterns as each wave passes through another in another scattering angle. Try also passing the laser beam through various kinds of corrugated glass and anytranslucent surface to discover even more intriguing pattern effects, such as rings, grids and many more.

  • Steve

    You’re on to it, Chuck.  The coherent laser light, when passing through a water droplet will reflect multiple times on the droplet’s surface creating multipath beams that interfere constructively and destructively producing light and dark areas.  The angle of the incident beam, the curvature (related to size) of the droplet, and the viewing angle of the observer are all factors in the pattern that is developed.  All three of those factors are changing from droplet to droplet in the photo, and that’s why you see a unique pattern in each one.

  • f2point8

    For starters the laser is not a steady beam of light. It is pulsating. Combine with long open shutter, raindrop prisms, individual lenses on the photosensor. I start looking into this combination of factors acting as a function.

  • Anonymous

    I’m not an optical physicist or anything like that, but my guess is it looks like the water droplets are refracting the laser light the same way it would for white light to create a rainbow.  However, since there is only green light and no red or blue or any other colors of the spectrum the other colors do not show, and therefore they show as black lines as a lack of light.  I suspect there is more than that going on, as “bruhinb” suggested there may be a polarizing filter at play here too.  Some detailed information from Jeremy would be really helpful to be able to recreate the effect.

  • Sterling

    The rain is causing the lines while the laser causes the cross hatch pattern. A similar effect is possible with a cross filter. Its just the wide aperature, rains vertical lines, and the lasers cross hatch beam pattern.

  • Guest

    But why are the droplets all appearing as septagons?

  • Nunucm

    The combination of aperture blades shape and the pattern on you lowpass-filter-pixels-in-your-sensor….. just as Moire is created.

  • http://twitter.com/denMAR Dennis Marciniak

    I’m no expert but it looks like he has four panes of glass on his windows that might be reflecting but I would definitely defer to a more scientific explanation and avoid this one.

  • http://twitter.com/TheCrazyLudwig Ian Ludwig

    The lens he is using has 7 Diaphragm Blades.

  • Anonymous

    Science or god aside, the result is amazing! Now I wanna go buy a laser pointer just to try this out.

    I wish it would just rain in Texas though. Kind of essential to the equation.

  • http://twitter.com/warzauwynn Daniel Hoherd

    That’s a standard bokeh characteristic.  Each element of the photo that limits or alters the rays of light that pass through it can do similar things.  The patterns are related to what was going on with the rays of light that were coming through the element that created the bokeh. It’s the same principle that lets you create bokeh stencils, and it’s the same principle that shows up in the background of this photo http://www.flickr.com/photos/warzauwynn/513118893/

  • Jao van de Lagemaat

    If you’ve ever worked with lasers you’ve seen patterns such as these: http://en.wikipedia.org/wiki/Speckle_pattern Combine that with out of focus diffraction on the aperture blades and you’ll get such standing wave patterns very easily

  • Jeremy Jackson

    Thanks all for comments and info.In terms of how I did the shot… I used a
    200 mW laser and had my aperture set to f/2
    (almost wide open). Focus was at infinity.I pointed the beam of the laser from behind
    the camera across the frame in front of the
    lens towards the background (my yard).The bright edges or lines are where the beam
    is hitting the background within the frame.

  • Phalgun P

    Looks like its the “Interference pattern” formed due to a coherent source of light which is the laser. Google for interference patterns.
    That’s a great photo though.

  • diablo

    This is a very well documented phenomenon, which it is actually used to measure droplet diameters. The technique is called interferometric particle imaging (IPI). It is the result of the interaction between the reflected light and light that has gone through the droplet once, and, as mentioned below, only happens when the light source us coherent and polarized.