stuck with DCG, always dim or foggy

[Dutchelm05]

Hey Danny nice to see you back posting. With John back I look forward to some great discussions

I read somewhere that to determine the right concentration of AmDi you should look at the transmission throught the film with the laser light. It should be about 50%. Can any of you guys confirm if this is your experience? I would imagine with the deep blue low power lasers that this is a bit more cridical.

In the lab at the crack of dawn before the family awakes and my day of making pancakes and soccer games begin. It is better to sacrifice sleep over family matters

Have a great weekend all!!

[Joe Farina]

I read somewhere that to determine the right concentration of AmDi you should look at the transmission throught the film with the laser light. It should be about 50%.

That's interesting, do you remember where you read it, Tony? For a relative measurement like that, a simple meter should work well, like a cadmium sulfide photocell attached to a multimeter. (A reliable laser power meter would be fine also, but after reading some posts on another forum, I'm beginning to have some serious doubts about my LaserCheck.) Offhand, 50% sounds like a lot of absorption, assuming blue light is available. The film should have good sensitivity to blue light, so low levels of dichromate can be used. With green light, much more dichromate is needed to get adequate sensitivity. If there really is 50% absorption at reasonably low dichromate levels, then that would be a strong argument for using a split-beam setup.

[Thieu]

Dave, yes, so far all my holograms with the casio diode were made with the raw expanding beam at about 4 feet distance. I'm also trying to find a way to circularize the beam. Things I've tried:

- prisms, actually I found out that these don't really have to be strictly anamorphic pairs, cause there is no need to compensate the dispersion. Almost any prism will expand the beam in one direction if the beam leaves it at an angle almost parallel to the surface. Apart from expanded, the beam will also become curved though and the losses are probably quite high.

-cyclindrical lenses. Over the last 10 years or so I've been collecting the optics found in laser printers. Some of them use cyclindrical lenses to shape the beam. With one of these lenses and another weaker (also cyclindrical) one I found that I could collimate the beam quite well in both directions. The focal distance ratio of the two lenses is about 5, so this should change the 10:1 to around 2:1 , but I haven't had time yet to set up the optics to expand the collimated beam again to see what it looks like.

- still playing with the idea of placing a rod lens fast axis collimator very close to the diode, but while not impossible, it's not easy to get it in place and mount it there. So far I haven't had the guts and right state of mind yet to try the uncapping on the real diode.

I've been very busy at work and there have been some stressful events privately as well, so I haven't been in 'the right state of mind' in general for doing holography. In about two weeks time things will be better again and I'll be able to experiment some more.

Thieu was this hologram made using no optics on the diode, as just an expanding raw beam?

[Dutchelm05]

That's interesting, do you remember where you read it, Tony?

Hi Joe, I am sorry to say I do not have the paper, it was from Rollison though that I am certain I do not recall the exact paper it was from. I just had it from a notebook from many years ago.

I think it would be worth noting however the next time one makes up a new batch of film especailly if it is successful. With single beams and with the advent of these new wavelenghts it would be worth knowing.

I am heading into the lab now, I will check my film at 458nm and report back later. If you hear any cussing in the next hour or so, you'll know things are not going well :wall: :doh:

[Dutchelm05]

Hey Joe,

Just to follow up
I get 68% transmission on my plates.
I guess much depends on the desired outcome. I've been trying to get yellow/gold and that is what I get (at least some of the time )
Perhaps it was refering to more broadband.
Anyway, it would be intersting to hear what others have as well.

Tony

[Joe Farina]

Tony, thanks for posting that. After giving it some more thought, I'm not sure how important the layer absorption (or beam ratio) is for DCG. I seem to recall Dinesh saying that large ratios of reference to object could still result in very bright DCG holograms. I know this is not true for reflection silver halide holograms, the beam ratio has a big effect, and should be close to 1:1 for optimum brightness. Also, consider Cristiano Perucci's very bright MBCDG holograms. With MBDCG the absorption is much worse, Kubota in one of his papers said it's around 90%. Yet Cristiano's single-beam reflection holograms look very bright indeed.

As for the amount of dichromate in regular "blue" DCG holography, it does of course influence speed (and I would assume lifetime of stored plates), and the amount of shrinkage (when that bulk material washes out of the emulsion during processing).

I personally put more emphasis on the shrinkage factor (when using blue light), and that's one reason why I like to use the minimum amount of dichromate.

[JohnFP]

Good morning guys,
I personally would say that there really is no way of checking the trasmitted:absorbed light ratio that can be used as an accurate baseline unless your objects were exactly the same like a mirror. Each object attenuates, modifies polarizes, reflects, scatters, diffuses, absorbs ect. the beam differently.

So I would say if 33% to 50% transmitts, this would be good for a mirror giving a 2:1 / 1:1 ideal SBR ratio.

But if we have an oject that is quite less then ideal, like a very porous, greyish object or an object with different colors then we may need 60 - 70% of the light to be transmitted.

I have alway found that the eye does pretty good at seeing light levels if the the two light levels to be compared are seen side by side.

So for SBR, just take 2 white cards that no light can get though and place them on each side of the plate coving about 1/3 of the plate on both side. Then stand at the side and look at both sides with very little head movement. On the one side you will see only the reference beam and on the back side you should see the light reflected only from the object. The object will receive a little more light (as you are coving 1/3 of the light that will go though the plate and hit the object) but if it is pretty close and just a little dimmer then the reference side, you will pretty much be AOK. If you really wanted to you could meter both sides of that plate and develop a formula for percentage of plate covering to what the ideal ratios would be.

Then one can adjust AmDi levels to allow more to transmit if needed.

I have not played to much with the blue yet, but my first batch of plates were made with 100:10:1 KDi. The yellow is barely seen. I doubt I have to go much lower on the KDi but will surely take some readings to stay with what others are working on here.

Don't forget, thickness of emulsion layer has a lot to do with transmitted light also.

As I stated before, I am going to make much thicker emulsions and I will start with the same forumula 100:10:1 as I saw some nice thick areas on my last batch that indicated the ratio and additional thickness will step up the quality and brightness of the holograms.

[dave battin]

hi you guys back from holoday! Im sorry for not responding eariler

I personally would say that there really is no way of checking the trasmitted:absorbed light ratio that can be used as an accurate baseline unless your objects were exactly the same like a mirror. Each object attenuates, modifies polarizes, reflects, scatters, diffuses, absorbs ect. the beam differently.

The testing base line is to test the ammount of light absorbed by the Amdi ? so i would think the way to do this, point your test probe at laser beam @ film-plane take reading (this is the the whole), and now introduce the film in it's film holder,then take reading seeing thru unprocessed film (this is the part),now the part/whole this is the ammount of light left. The only constant need to be the wavelenght..........?

[Danny Bee]

you know you can go down lower that 1% with uv I had too, but like john said its the thickness too that plays apart in all this, i would try but i burn up both diodes i had,but i know it could go down much more, anyway dave is making me a new ultra blue so i will test later with the new Ultra Blue and the C.A.B system kit that im working on for ultra bright Holograms & deep :dance:

[dave battin]

anyway dave is making me a new ultra blue so i will test later with the new Ultra Blue and the C.A.B system kit that im working on for ultra bright Holograms & deep :dance:

yes yes! you and the line of people behind you!

ive posted some "tips for tuning the 445nm beast" in the other thread. I am anxious to see other holographers succed with these diodes as well. I'm thinking a thread on "building/testing" would benifit All ,rather than hi-jacking this thread?