I agree with your analysis on the relationship between brightness and the diffraction efficiency of individual wavelengths. My simple word of "1/n^2" is not an accurate description of diffraction efficiency. Because the color hologram uses different wavelengths to record, even if we apply the "1/n^2" theory, the result is not considering the wavelength differences. As the shorter the wavelength, the higher number of Bragg layers recorded in the same thickness of emulsion. Also, the shorter the wavelength, the ratio of AgX crystal size over wavelength increases. So the actual relationship is very complicated. I was just using a "qualitative" equation to mention a "quantitative" phenomena.Dinesh wrote:So, to relate the brightness of a full colour hologram to the efficiency of the hologram, the efficiency must be given for each wavelength component in the hologram. However, there is a calculation by John Caulfield (I believe) that states the if you record n holograms on the same medium with the same wavelength, then the efficiency of the final hologram is 1/n^2, where n is the efficiency of just one recording, assuming that all the recordings are independant. Thus, if you shot an H2 with, say, 5 H1s all perfectly exposed and developed, then the final hologram has an efficiency of 1/25th of the hologram if you only used 1 H1. That is, the more holograms you superimpose, with the same wavelength, the faster the final hologram efficiency drops. There are some problems with Caulfield's analysis, but his analysis was made in the 60s, when holograms were not generally bleached. So, the analysis works for unbleached holograms. It breaks down if you bleach the hologram.
Even if the single wavelength diffraction efficiency of multiple-exposure or color holograms is lower than the diffraction efficiency of the single-exposure monochromatic holograms, it can be reached to high enough (theoretically to 100%) as long as the thickness of the emulsion, index modulation, and the low absorption of final processed emulsion are satisfied.
Let me describe in more detail about my stating of color saturation and AgX crystal size. For single-exposure monochromatic hologram, if it is processed in AgX solvent developer, the size of filament silver is significant large compared to the size of original AgX crystals. When those large size silver filament is bleached to AgX, the newly formed AgX will deposit to the AgX crystals in the unexposed zone of the emulsion. Thus, the micro structure of Bragg layer is slightly changed ( i.e. the sharpness of the Bragg layer is changed or the Bragg layer thickness is changed slightly). This is the main reason of increased spectrum width of reconstructed images. Increased spectrum width leads to lower color saturation.Dinesh wrote:The colour saturation is the proportion of a primary colour to the overall colour (S = Chroma/Lightness*). Therefore, I would think that the colour saturation would depend on the bandwidth of each component as a ration of the sum of the bandwidths of all the components. That is, by the Fourier coefficiant of one of the primaries to the sum of all the components. I don't think this has anything to do with the crystal size, assuming that te crystal size is small enough to record the appropriate spatial frequencies for the different wavelength components. If the crystal are too large to record the spatial frequencies, on average, then there will be no recording at all.
Russian emulsion usually apply the semi-physical developing which generates the colloidal silver. The size of individual colloidal silver speck is very small but the colloidal silver "cloud" is in huge size (depending on the processing time). What I found is the semi-physical developing results in strong color blurring.
Thanks. I am now far from US and don't know what is PCGG4. I googled PCGG4 but don't get a meaning one. Could you send me a private message telling me your name? I saw your posts in this forum and previous one for a decade but sill don't know who you are. Thanks.Dinesh wrote:By the way, Danny brought one of your holograms to PCGG4. It was pretty good. Danny compared your hologram to my full colour holograms and the opinion was that the brightness was about the same (Danny's conclusion, not mine!). Mine were made on Colourholographics pan material, which he (unfortunately) no longer makes. I'm finding it very difficult to use PFG-03C. Danny has left me with some dye, so I'm going to try the experiment he suggests, put the dye into a fine-grain Slavich material and shoot full colour.