opal

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Brian
Posts: 48
Joined: Thu Apr 07, 2016 8:31 am

opal

Post by Brian » Fri Apr 12, 2019 6:02 pm

In this post I display a photograph of an Australian black opal with strong red play-of-color sitting on a black acrylic plate. The elliptical opal is about 1 cm along its major axis. In the photograph, the opal is illuminated by a white light LED from below, tilted toward the opal at an angle of about 30 degrees from the plate upon which the opal rests. The reason for posting the picture of the opal is for comparison with a reflection hologram of the opal displayed in the next post.
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DSC_1990 (2c).jpg
DSC_1990 (2c).jpg (291.7 KiB) Viewed 1937 times
Last edited by Brian on Sun Apr 14, 2019 2:44 pm, edited 2 times in total.

Brian
Posts: 48
Joined: Thu Apr 07, 2016 8:31 am

Re: opal

Post by Brian » Fri Apr 12, 2019 6:15 pm

So here I display a photograph of a reflection hologram of the Australian black opal with strong red play-of-color. The hologram is illuminated by a white LED light almost exactly as the opal itself was. So... seems like no big deal, a reflection hologram made using a red laser. But take a closer look... notice the white light reflection along the lower left edge of the opal. How was that reproduced?
DSC_2017 (2c).jpg
DSC_2017 (2c).jpg (1018.73 KiB) Viewed 1979 times
The cool optics about opals is, of course, their play-of-color... colors flashing and changing as you change the orientation of the light source or the orientation of your eye. You can't reproduce this effect with a still photo. I don't have a nice movie to demonstrate, so you'll just have to believe me: as long as the light source is illuminating from somewhere below the hologram, the hologram does reproduce the opal's play-of-color.

Of course, the opal's play-of-color arises from light wave interference. So a hologram of an opal is an interferogram of an interference effect.

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