Hologram Exposure Times based on Microjoules

[holorefugee]

Re the beers, give me a few weeks notice and I'll brew a batch! If you want to play with dcg let me know and I'll coat a few plates

Those both sound great, I'll keep you informed on my plans. I've never had home brewed beer!

Jeff

Home brewed beer is the best and worst beer I have ever had.

[John Sonley]

Of course, all of this depends on the dev/bleach combination, the the numbers of 2 minutes to OD of about 2 and 2 minutes to bleach to clear are a good benchmark to check exposure. The actual OD you take it to depends on the grain density, and varies from film to film. As I remember, for instance, 10E75 needed to be "20% black" for transmission and, with 8E75, "80% black" for reflection, which seems to translate to an OD of about 0.2 or 0.3 for Tx and about 0.8 for Rx. But, it still needed about 2 minutes to go to the prescribed darkness.

I feel a kinship with your 2:2:2
I frequently use CW-C2 and a Ferric EDTA bleach with H1s and also H2s, when I want to move towards gold/orange colours of the finished hologram and I find that if I expose my old Agfa film for 60 - 75 secs, I can just see a very faint quantity of light from my green safelight when I look through the film - I'm guessing at OD about 2, then develop for 2 minutes in CW-C2 and I guess it takes about 2 minutes to clear, or slightly less
With those settings I've had some really bright H1s and H2s.
In general though I reduce exposures a bit for H1s to go for a lesser OD

From the graph I've drawn from the CdS cell calibration chart, that equates to 150 microjoules/cm-2 .... which looks about right
Reading one of your replies I get the feeling that you use your 2:2:2 with D19 + Ferric Nitrate bleach.
Would you expect D19 to behave in a similar manner to CW-C2
BRgds
John

[Ed Wesly]

Agfa would give ridiculously low sensitivity readings to get a density of only .6, which is usable for an unbleached holo but not the densities needed for bleached ones. Some batches of plates were slower than others, and there would be a need to blast them all the way up to 400uJ/cm^2.

[Ed Wesly]

"10E75 needed to be "20% black" for transmission and, with 8E75, "80% black" for reflection, which seems to translate to an OD of about 0.2 or 0.3 for Tx and about 0.8 for Rx."

Baloney!

Density = log 1/transmission; if your 20% black translates to 20% transmission, then its density is .69, which is pretty dark. But I am guessing that what you mean is if it is 20% black means it is 80% transmissive, so its density is therefore .096 or .01. Then your 80% black means 20% transmission, which brings us back to the first sum, a density of .69 only.

A density of 1 = 10% transmission; density of 2 = 1% transmission. Unless you have a densitometer it is hard to assign these numbers, unless you are comparing the holographic plate to a calibrated step wedge.

[Dinesh]

But I am guessing that what you mean is if it is 20% black means it is 80% transmissive, so its density is therefore .096 or .01.

Yes. The figures I was quoting were the instructions taken from Fred's book, and given to me by Edwina Orr and Peter Miller (two of my mentors) while I was learning holography. The common wisdom back then, in 1981 and using Agfa 10E75, D19 and Ferric bleach for Tx; Agfa 8E75, Pyrogallol and Van Ranesse for Rx, was that the transmission holograms were to be taken to "20% black" and reflection holograms were to be taken to "80% black". Peter showed me what "20% black" meant by getting me to look at the safelight through the plate. The plate was meant cut the safelight by 20% and the plate looked a dark grey in white light. Peter also showed me what "80% black" meant and that seemed to mean that the safelight was all but gone. Bear in mind that back then bleaching was an added extra. A lot of the holographers didn't bleach and bleaching was "recommended" for a brighter hologram. Today, of course, bleaching is part of the de facto development process. At any rate, I quote from Fred's book :

Transmission holography (p. 152 in my edition)
"Proper development is usually in the range of a density of 15% to 20%, and is usually determined by trial and error"

Reflection holography (p. 171 in my edition)
"These plates are developed to a much greater density than transmissions. You will want to go to 70% to 90% dark or let only a third to a tenth of the light pass through (density of 1.0 to 2.0 for you photo people)."

if it is 20% black means it is 80% transmissive, so its density is therefore .096 or .01. Then your 80% black means 20% transmission, which brings us back to the first sum, a density of .69 only.

Again, yes. The figures I gave were off the top of my head from 30 years ago.I think I said 0.2 and 0.8, so I guess I was off by an order of magnitude on the transmission and about 13% off on the reflection. Today's emulsions need to be taken a lot darker than the magic "20% dark" and "80% dark" of yesteryear!

Would you expect D19 to behave in a similar manner to CW-C2

No. The gamma for CWC2 is very different from D19. I don't have exact figures (difficult to get gammas of developers), but I believe that CWC2 is quite a bit more aggressive than D19. D19 was used by photographers as a "high contrast" developer which, I believe, was why it was used by the early holographers. However, high contrast in the photo world is around about 10's of lines/mm, as opposed to 3000 lines/mm for holography.

Home brewed beer is the best and worst beer I have ever had.

Chris Cochran (senior guy at Stone, you may know him) said the same thing, tried my beer anyway and was surprised at how good it was. I told him I was trained by experts - Colin Kaminsky and Dennis Middleton (local brewing guru - you may know him too).

[Ed Wesly]

The baloney I was referring to was your translation of % to density. You should know better on how to do that!

But I will also add the epithet to the figures given in your references, they were punting also, since density is not measured in percentages.

I guess the bottom line is to ignore quantifying the "darkness" unless you have the machine. Do the test strips, see when the magic happens, make another test strip, fix instead of bleach, and leave that as your gold standard if you want to develop to a target density.

[holorefugee]

I am at the other end of this post. I do all my developing by feel. I stopped using a clock long ago. When it looks right it is right. When it develops too fast I lower exposure. I like short exposures and long development. I have made very bright holograms with PFG-01 and D-19. It is not my first choice but it can be done. My brightest holograms have been on BB-640.

I still use a light meter for H1 to H2 copies but the "shadow" method Dinesh taught me works very well.