The image above was the first version of this photo. I used a flourescent light table as my illumination source, and overexposed for transparency. I combined three different exposures, each with a different shutter speed but the same aperture, to get the effect I wanted (see exposure details below).
Lately, I’ve become interested in photographing flowers either on a white background (because backlit transparency of flower petals is beautiful) or on a black background (because the high contrast with the flower makes color values pop). When I can, I’ve created both white and black versions. Sometimes photographically, but more often using Photoshop inversions, as with the hellebore inversion of the original image below:
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[Both images: Nikon D300, Sigma 50mm f/2.8 macro lens (75mm in 35mm terms), three exposures (3 seconds, 5 seconds, and 8 seconds), all at f/32 and ISO 100, tripod mounted.]