color holograms!

These are all of the old posts from the first two years of the forum. They are locked.
Updated: 2005-03-28 by HoloM (the god)
JohnFP

color holograms!

Post by JohnFP »

Very nice Dinesh. I wish I was there to see the look on your face when it turned out.
JohnFP

color holograms!

Post by JohnFP »

Do you mean you changed the reference angle for the second exposure?
Dinesh

color holograms!

Post by Dinesh »

"Do you mean you changed the reference angle for the second exposure?"
No. Same reference. If I'd changed the reference both images would not be simultaneously visible.
Dinesh

color holograms!

Post by Dinesh »

You'd have seen total amazement. Joy cut the two 4x5's film (in total dark!) into 4 pieces each. I had no idea about exposure so I used the exposure I normally gave BB520 (~1 mJ) to both red and green. Processing in the dark, I couldn't tell how long to leave it in the developer so I left it in for about two and a half minutes, my usual rough time for Silver with CWC2/PBQ. It was also difficult to know when the bleach cleared the plate. So I went through 3 plates blind. Nothing! Then I remmbered Mark Cavin saying that he used a very dim white light and got no fogging so I tried an orange LED with the current set low (Thanks, Mark!). This enabled me to see how dark my processing was going and when the plate bleached. However, using my old Silver techniques I was getting nothing. With only two plates left and panic setting in, I looked around on the internet for anything on BBV ppan plates. I remebered Kaveh's site had an article on it, but that was down (to me, anyway). It's amazing the lack of information on BB plates in general! Anyhow I found a paper by a group using BBV Pan to make multiple line filters. They had sensitivity curves! The red is a lot less sensitive than green and blue is most sensitive of all. Roughly,
blue => ~0.5 mJ/sq cm
green => 1.2 mJ/sq cm
red => 2.4 mJ/sq cm
for maximum efficency. So I set my 514 exposure to 1.2 mJ and 633 to 2.4 mJ. Something! Dim and unrecognisable, but something! One more plate to go and panic really sets in. Then I reason: There are two sets of fringes in there.The darkness of the emulsion is dependant on the ratio of reduced Silver to Halide. Each set of fringes will give a particular value for this ratio. Two sets of fringes will give a higher value to this ratio. However, this must have a higher average spatial frequency if you just count fringes regardless of "color" in the fringes and also, I don;t know the relative strength and distribution of 'red' fringes to 'blue' finges so I can't develop for too long. With one film to go, the question is: Latensify or try a faster developer? I flicked a mental coin, tried another developer (AAC), and voila! It worked! Of course, if I'd latensified, it might have worked better. If I can persuade She Who Holds The Purse Strings, I'm going to get a box of PFG-03C.
JohnFP

color holograms!

Post by JohnFP »

Your keeping me hanging. If it is propietary I understand but what did you do?
dcgman

color holograms!

Post by dcgman »

"The BBV pan film is exceptionally clean but the presensitization in pitch black ain't easy"

Just a thought- has anyone working with pan films tried using night vision goggles to view what they are doing in the dark? May need an infra-red lamp, but should be do-able
Bob

color holograms!

Post by Bob »

I've been working with Slavich PFG-03C plates recently and have found that a couple of indicator lights, and a few micro-light leaks around the room let me see as well as needed, provided a little quiet time to let me eyes adapt to the dark. Besides, it's a little creepy to think of myself walking around in the lab looking like Mr. "Silence of the Lambs".
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