how to determine exposure time?

Tony · Post by **Tony** » Fri Apr 30, 2004 4:34 pm

Bob-

I think you are referring to the fact that the dry powdered component ingredients in D-19 could separate due to different densities, and the resultant powder might not be uniform. I was concerned about this too.

However, I was more concerned with mixing more D-19 than I could use, and generating (even) more hazardous waste to deal with. So I bought a Gallon-sized bag of D-19 ($6). I mix it 2.75 dry ounces to make 1 Liter of developer. This is 1:1 diluted from what the bag says. Before measuring out the powder, I rotate the bag in the vertical plane for several minutes to mix the ingredients.

Reasonable results so far...

Bob · Post by **Bob** » Fri Apr 30, 2004 5:05 pm

The triumph of technique! That's what leads to the best results in holography. Holography itself is a technique, and one that requires attention to all the little details or we get nothing (or worse yet, dimmies!). Think about how little movement it takes to make a hologram dim (presuming everything else was perfect). Or the tiny departure from optimum conditions in the processing baths that leads to "milkiness".

Dinesh · Post by **Dinesh** » Fri Apr 30, 2004 5:19 pm

" It is very high contrast, I believe that means it has a high gamma, which would make exposure and developer times critical. Are these conclusions correct? Dinesh?'
True. The gamma is a measure of how fast the density changes as a result of exposure. This is necessary for holographic film due to the extremely high change in density over a very small area of the film. Small variations in exposure can lead to fairly high changes in density for high gamma film, similarly for development. The ratio is also pretty important since a small variation off the "center" exposure can take you into the non-linear region. For a single beam Denisyuk, you'd need to have a diffusely reflecting white object close to the plate.

Dinesh · Post by **Dinesh** » Fri Apr 30, 2004 5:26 pm

"Think about how little movement it takes to make a hologram dim "
And yet, I've shot holograms over a rumbling underground train. I even shot a succesful-ish one in the middle of an earthquake! My shutter was open when the earth moved (Due to the 'quake! Honest!) I rushed out of the building and came back in some 5 minutes later with the shutter still open. Since this was supposed to be a 10 second shot I didn't have a hope in <down there> of getting anything. However I developed anyway and actually got a so-so hologram. Not that I'm suggesting ignoring movement problems - these are fairly important and you need to make sure of stability, but sometimes it seems like a black art! I remember talking to Paul Newman (the holographer, not the actor) and telling him how I was beginning to figure it all out. His comment was; "And just when you think you know it all, it comes back to bite you."

Bob · Post by **Bob** » Fri Apr 30, 2004 5:58 pm

What Paul said is true. And the things that come back to bite are the fundamentals! That's why I like this forum ... it keeps the fundamentals up front. The next system I'll probably be setting up includes 8 beams, co-aligned masks with 10 micron features and anamorphic optics, all within a 2'x2' space on the table. The things that could muck it all up and completely blow the deadline are the same things discussed here all the time. Could be water pressure variations pulsing through the laser, something touching the table and blowing its isolation, wandering beam pointing, or maybe the dreaded mode hop! Well, it actually can't be a mode hop because I'm not using an etalon, but you get my drift! 8^)

Tom B. · Post by **Tom B.** » Sat May 01, 2004 3:54 am

I'm not sure about this particular problem, but since being alerted to potential problems with residual developer, tapwater chlorine and dissolved calcium and other stuff interacting with my (usually FeIII) bleach, I have soaked my plates in distilled water for about 30 sec just before bleaching, after having rinsed them in running lukewarm tapwater for several minutes to remove as much developer as possible. I think it helps to produce a cleaner result, but have never tried a test with and without distilled water pre-bleach rinse.

Jeff · Post by **Jeff** » Sat May 01, 2004 4:39 am

How much development time?.- A test method: Leave a small piece of plate in very bright light for a while and then leave it in developer for 5 mins. so that it goes as dark as possible. Rinse and dry it. Now when you develop your holograms under safelight you should use this dark piece of plate to look through at the safe light (it will still have some transparency). You then know that your holograms must never go as dense as that or you have gone too far on developing. .It is OK as a working principle to take your plates to no more than half that density in their darkest areas by looking through at the safelight filament with one eye shut. (Plates continue to develop well in air without staying in the dev. bath all the time.)

(This was lifted from http://cabd0.tripod.com/holograms/id1.html)

Martin · Post by **Martin** » Sat May 01, 2004 5:30 am

"It sounds to me like you may be using a developer that is unsuitable for holography."

Dokumol has been a fairly popular "holographic" developer - at least in Europe. Its success may have been related to Nick Phillips's advocating for Tetenal products like "Neofin blau", said to produce outstanding low noise.

"What's wrong with D-19?"

Nothing, I assume both D-19 and Dokumol (or Neutol etc. etc.) are very forgiving developers. I guess the whole thing boils down to availability. I assume in certain European countries Tetenal's products are much easier to purchase than most Kodak products.

Jeff · Post by **Jeff** » Sat May 01, 2004 5:46 am

Just adding to what Tony said.
"Dichromate" bleaching usually means a "reversal bleach" or one that removes developed up silver as SOLUBLE silver dichromate/sulfate salt, leaving behind your holographic fringes in the form of virgin silver halide grains that did'nt get developed up. So it is essential to prevent
dissolved up silver from redepositing itself as a crude precipitate all over your hologram as a white scattering layer. The chief cause of this milkiness is actually the
soluble bromide ions in the developer and even if you make your developer without any potassium bromide added initially, (which I personally prefer) you still get bromide and iodide ions released in the developer that were originally partnering the released silver. So to prevent this form of milkiness without using large quantities of distilled/deionized water I recommend a very thorough TAP water wash after the developer step. This is to remove all traces of those soluble bromide/iodide ions.
The chloride ions in the tap water form a silver halide which is more than 10 times more soluble than those, so you can simply wash them out with a moderate amount of deionized water before you go into the dichromate bleach bath. But you must remember that AFTER bleaching it is essential to first wash the hologram again in deionized water because the gelatin is "full" of dissolved silver ions longing to redeposit themselves by partnering up with soluble bromide ions. Once you have cleared out all that dissolved silver you can wash with tap water if you want.

Just a note about the Non reversal bleach systems such as the copper sulfate one on :
http://cabd0.tripod.com/holograms/id1.html
In this the whole system is packed full of bromide ions
and deionized water is irrelevant, tap water is quite good enough in my neck of the woods.
Jeff

Martin · Post by **Martin** » Sat May 01, 2004 8:04 am

That was interesting! How about adding 1g/L of EDTA to a reversal bleach, would that "solve" the problem?