broad/narrow DCG and LEDs (photos)

[Joe Farina]

The first photo shows a broadband DCG hologram by August Muth. The illumination source was combination of two LEDs, a green one (~520nm) and a red one (~630nm), cemented together (second photo). Both emitters (combined) only have a total size of ~4mm, so this is more than enough "spatial coherence" to illuminate holograms, even at close range. I wanted to post this photo because it shows very clearly the blurring effect of broadband DCG holograms. Areas near the film plane are sharp (note the fellow's right hand -- it's not blurry). By contrast, the fellow further back (looks like a mummy with horns) has two clear images, a green one and a red one. Note the horns -- just below the green ones are some fainter red ones. This is an image-planed hologram, and the rim of the bowl sticks out in front of the film plane quite a bit -- notice the second red "rim." With a white light reconstruction source, this would normally appear as a smooth blur as the various wavelengths are diffracted. But here, with only green and red, the effect is very easy to see.

The last photo shows a narrowband DCG hologram illuminated with green only. It's quite sharp, all the way back. My hologram has a lot of defects though. The first hologram would also have been sharp, if only red or green was used (but less bright compared to white illumination).