Search found 401 matches

by Din
Fri Nov 24, 2023 10:35 am
Forum: Off Topic
Topic: Whatever Became of Holography?
Replies: 19
Views: 27145

Re: Whatever Became of Holography?

When the reference and object beams are in air, the replay polarization dependance is very small, and can easily be disregarded by inclusion with scatter, absorption and Fresnel reflections (which are seldom measured). When making "edge-lit" holograms, or HOEs where at least one of the be...
by Din
Fri Nov 24, 2023 10:16 am
Forum: Off Topic
Topic: Whatever Became of Holography?
Replies: 19
Views: 27145

Re: Whatever Became of Holography?

This is from R.R.A. Syms "Practical Volume Holography" (Oxford Engineering Scientific Series), Oxford Science Publications, 1990, page 184: "Even for weakly modulated gratings, coupled wave theory predicts a considerable difference in diffraction efficiency between the two possible r...
by Din
Thu Nov 02, 2023 12:39 pm
Forum: Off Topic
Topic: Whatever Became of Holography?
Replies: 19
Views: 27145

Re: Whatever Became of Holography?

Unfortunately a sub-group of display holographers has swallowed the idea of picture meaning an actual picture of a cat, for example, and get pretty nasty when the idea of 'picture' in the scientific sense of information is broought forward. I don't know if you're referring to me or not, Din, but I'...
by Din
Wed Nov 01, 2023 12:01 pm
Forum: Off Topic
Topic: Whatever Became of Holography?
Replies: 19
Views: 27145

Re: Whatever Became of Holography?

I have always felt that "holography" should only be considered a method (or tool, component, etc.) for a much more general purpose. When a person sees a hologram, and says "what is it?" the answer should be ___________ (fill in the blank, something other than "it's a hologr...
by Din
Mon Oct 30, 2023 12:15 pm
Forum: DCG
Topic: Angular Bandwidth in DCG
Replies: 10
Views: 8791

Re: Angular Bandwidth in DCG

Joe, You need to be careful drawing conclusions on angular bandwidth as it applies to the kind of holograms you make, as opposed to the kind of hologram used in their paper. Firstly, they're using an old method of making dcg plates by taking a silver halide plate (Kodak 649F), fixing out the silver ...
by Din
Tue Oct 24, 2023 1:01 pm
Forum: Off Topic
Topic: Whatever Became of Holography?
Replies: 19
Views: 27145

Whatever Became of Holography?

https://www.americanscientist.org/article/whatever-became-of-holography An article in American Scientist by Sean Johnston; some of you may know him as having received a grant to write the history of holography, he was a presence in a lot of the conferences about 10 years ago ( https://global.oup.com...
by Din
Mon Oct 23, 2023 5:59 pm
Forum: Gallery
Topic: recent DCG hologram
Replies: 4
Views: 13560

Re: recent DCG hologram

Nice. Wonder what difference it would have made if just 532 or 488nm. Jody, The sensitivity of dcg at 532 is close to 1/5th of the sensitivity at 488. So, assuming no dyes were used, just exposing with 488 would have made little difference. The image may be just a little more narrow band, but the e...
by Din
Tue Oct 17, 2023 8:43 am
Forum: DCG
Topic: Purple transmitted light in DCG
Replies: 3
Views: 4588

Re: Purple transmitted light in DCG

Your hologram seems to reflect mostly in the green. Therefore, what's left in the transmission, ie what's taken away from the reflected light, is red and blue, which makes purple. The brighter the hologram, the more green is reflected, and the more purple is the transmitted.
by Din
Thu Oct 12, 2023 8:53 am
Forum: DCG
Topic: Angular Bandwidth in DCG
Replies: 10
Views: 8791

Re: Angular Bandwidth in DCG

Remember also, if there's water in the film, you have to fix for longer to draw out the water. Don Broadbent and his student Augie Muth both had humidifiers in the coating room to control the water content that seeped into the film during the drying phase. If you don't draw out the excess humidity,...
by Din
Mon Oct 09, 2023 12:24 pm
Forum: DCG
Topic: Angular Bandwidth in DCG
Replies: 10
Views: 8791

Re: Angular Bandwidth in DCG

Dave, yes, all of the things you mention will affect spectral response. Thickness: The thicker the emulsion, the more the differential swelling, because, as I said before, the top layers of the emulsion continue swelling as the water penetrates deeper into the emulsion. This means that for a thick e...