5 ms·

Wow, reading the wiki article on Lippmann plates, sounds almost like a hologram - baking a diffraction pattern into glass that is then 'replayed' by white light

• andreareina 2y ago
  My read is that you can't make "prints" of it like you can with regular negatives. You probably could use a copy camera to make a copy of the plate but you're going to lose fidelity that way.
• mhalle 2y ago
  Lippmann photographs are like holograms, specifically reflection holograms. The image is exposed using self-interference, which works in what we would typically consider incoherent light due to a very short distance between the light and its reflection. Development of the plate produces a superposition of many different volume diffraction gratings mostly parallel to the surface of the plate. If the plate is bleached, these diffraction gratings become high efficiency phase gratings. For playback/viewing, light from the illumination source is both diffracted and filtered in wavelength by the volume diffraction gratings. In a hologram, the diffraction gives the multiple perspectives that make the medium so cool. For Lippmann photographs, the camera has removed most of the perspective information and the dichroic or interference filtering of the gratings is the primary effect. In either case, the final image is a layer free image bearing volume in the emulsion. That's why it can't be effectively copied using 2D techniques. Since the image is 2D (maybe slightly 3D? I'd have to think about that), it can be copied using a standard photographic technique. But the interference gratings in the emulsion have some angular dependence on the light source and viewer's angle that wouldn't be present in a 2D copy. In this way they also look a bit like a reflection hologram.
  • jazzyjackson 2y ago
    Thanks for the keywords, there's a lot I need to learn to grok holography Regarding perspective through a lens, I'm imagining looking through my stereo microscope vs my SLR ... Does the fact that a lens has a single focal point get in the way of keeping depth information ? Or could I split the image landing on the mirror into two and have a 3d stereo viewfinders for my Nikon camera, such that the view is stereo and it's only the film that's throwing out what direction the light is coming from... I'm reminded of the Lytro Illum lightfield cameras, they only leaned on "focus after the fact" gimmicks, maybe if they tried it during a VR boom to share "spatial photographs" they would have had access to a new market
    • simne 2y ago
      > Does the fact that a lens has a single focal point get in the way of keeping depth information ? No, really single lens have separate focal point for each wavelength, but achromatic optical system in SLR have at least two lenses, so they have range of frequencies for which focal points are very close to one designed point. Mirror optical system don't have chromatic distortions, but in SLR case lens just cheaper to produce. Lytro using other idea - light field from short distances is not square but rounded (square light field from distant stars, because of very large distance, so radius too large to see rounding), and in Lythro each point seen via prism by few pixels (each angle with other pixel), so could measure distance to light source and using this info, restore distance information. Unfortunately, Lythro technology means, with few Megapixels CCD, will have just some hundreds Kilo-pixels restored image, so in reality, need some hybrid approach, where will be classic high-resolution 2D and some sort of depth sensor. Plus, need additional processing power to calculate restored image. So yes, in reality, latest Lythro camera using huge CCD and very powerful processor, all too expensive for COTS (but acceptable in some cinema niches). Anybody could make Lythro-like setup from ordinary lens and CCD (and make calculations on for example Raspberry), but now Lythro patents prohibited to make money on this.