Discover mag article

Dinesh · Post by **Dinesh** » Sun Nov 30, 2003 1:59 pm

"..which makes me wonder if a "dag layer" could be spectrally sensitized."
From the processi was reading, you infuse iondine and/or Bromine into the Silver layer. This is apparently grainless. I was wondering if the mechanism was that you were making Silver Iodide without a grain structure, ie direct interaction of light with the AgI molecules. Then I realised that AgI probably was ionically bonded, which means the minimum feature would be a single cube (assuming a cubic structure), ie one lattice structure. I was trying to find out the spatial frequency response and thought that if the minimum feature size was one lattice, then the diagonal on the cube would give the spatial frequency. So that if the bond length were a, the the spatial frequency response would be 1/(2*3*a^2). However, if that is the mechanism, then I suppose a dye could be found that would transfer energy to the lattice, causing the lattice to break down and ionize. Along this mode of thought (and very fanciful!) I wonder if a corona discharge would create an image, since the electrical energy would also ionize the AgI. I remember electrolyzing molten NaCl as a child to get Sodium so I could throw it into the bath!

photolytic · Post by **photolytic** » Fri Dec 12, 2003 10:00 pm

M. Susan Barger (c 1990) tried unsuccessfully to sensitize the daguerreotype with typical silver halide sensitizing dyes used in gelatin emulsions.

However the spectral sensitivity of the Daguerreotype plate should not be a problem now that 405nm diode lasers are available.

I see that no one responded to the question of the sensitivity of hologram plates. I'm trying to order some to do that myself. I got no response from my contact through the 4th dimension website yet. Any suggestions?

Dinesh · Post by **Dinesh** » Sat Dec 13, 2003 1:45 am

Well, I sort of tried by asking if anyone had a translation of ISO figures to J/sq cm. Since holographic film is measured in J/sq cm due to the fact that it's sensitivity figure is based on coherent light whereas photographic film is based on radiometry, it's probably not easy to do this translation. Also, there are questions of MTF and spatial frequency respone. In holographic film, the sensitivity drops off at higher spatial frequencies, so in order to give a figure for sensitivity you need to get a figure for spatial frequency response. I doubt anyone has these figures unless they've measured them by shooting on Daguerretypes. It may be possible to get these figures by modelling the process, which I sort of tried to do but got no feedback, so I have no idea if I was vaguely succesful, or whether the more knowledgable amongst us are rolling around laughing at the suggestions about spatial frequency response I made!

Martin · Post by **Martin** » Sat Dec 13, 2003 2:14 pm

"However the spectral sensitivity of the Daguerreotype plate should not be a problem now that 405nm diode lasers are available. "

If I am not misled silver iodide is sensitive up to ~550 nm.

Anonymous · Post by **Anonymous** » Sun Dec 14, 2003 1:18 pm

I believe you have been slightly missled. Early photographic processes from the Daguerreotype and the wet collodion process up to the gelatin dry plate were only sensitive blue to green light. Hence the problem Maxwell had in producing the first color image in 1867. The addition of silver bromide along with silver iodide does incease sensitivity to greenlight, but panchomatic plates and film were not developed until the introduction of sensitizing dyes.

Anonymous · Post by **Anonymous** » Sun Dec 14, 2003 1:21 pm

In my recently published work for the 2000 issue of the Daguerreian Annual, I found that a multiply sensitized Daguerreotype plate (Iodine + Bromine) required a white (4800K) light exposure of 4 foot candles or 43 lumens / sq m to produce maximum highlight brightness.

Let’s assume that the wavelength of our laser is 555 nm, where 1 joule/sec = 683 lumens.

Then 43 lumens / sq m would be the equivalent of 0.063 Joule/sec sq m

Does this help you calculate the relative speed of the holographic plate vs the Dag?

Martin · Post by **Martin** » Sun Dec 14, 2003 2:21 pm

"Early photographic processes from the Daguerreotype and the wet collodion process up to the gelatin dry plate were only sensitive blue to green light. Hence the problem Maxwell had in producing the first color image in 1867. The addition of silver bromide along with silver iodide does incease sensitivity to greenlight, but panchomatic plates and film were not developed until the introduction of sensitizing dyes."

Agreed. My "If I am not misled silver iodide is sensitive up to ~550 nm", referred to silver halides being sensitive from UV - 550 nm.
Historically, things might have been much subtler though since Becquerel (~ 1840) was able to get some slight reactions from light > 550 nm.
I wonder about a possible knowledge of sensitizing silver halide emulsions to longer wavelengths (prior to Vogel's introduction of dye sensitization in 1873): e.g. adding colloidal silver might have greatly extended the spectral sensitivity of a photo emulsion.

John Hurlock · Post by **John Hurlock** » Sun Dec 14, 2003 8:06 pm

Please forgive the errors in my last post.
What I meant to say was that Daguerreotype plates required a white light exposure of 4 foot candle seconds.

Since 1 FC =10.76 Lux = 10.76 Lumen / square meter,

4 foot candle seconds x 10.76 = 43 lumen seconds/sq m.

Let’s assume that the wavelength of our laser is 555 nm, where 683 lumens = 1 joules/sec.

Then 43 lumen seconds/m2 would be the equivalent of 0.063 J/m2 or 6.3 microjoules/cm2

According to the forth dimension holographic website VRP-M mastering in Geola holographic Systems requires an exposure of 20-40 microjoules/cm2

Does this mean that Daguerreotypes would be 3 to 6 times faster than VRP-M holographic plates?