My latest large MBDCG holo

Cristiano_Perrucci · Post by **Cristiano_Perrucci** » Sat Apr 21, 2007 11:54 am

Hi all,

this is my latest MBDCG holo (H2).

The backgrond is around 5cm depth while the violin is about 1cm from the plate.

Cheers,

Cristiano

MichaelH · Post by **MichaelH** » Sat Apr 21, 2007 1:18 pm

Very pretty! Can you tell us a bit about how it was made? It looks very broadband, almost white-ish in areas.

Cristiano_Perrucci · Post by **Cristiano_Perrucci** » Sat Apr 21, 2007 7:07 pm

MichaelH wrote:Very pretty! Can you tell us a bit about how it was made? It looks very broadband, almost white-ish in areas.

Both H1 and H2 are Denisyuks.

H1 is a quite narrow band reflection on red, H2 it's a real broad band as seen in the picture.

As well known red narrow band for H1 is mandatory if the target is a copy.

Cris

Sergio · Post by **Sergio** » Mon Apr 23, 2007 7:12 pm

Congratulations!

This is a master piece of MBDCG work, I know now that the MB dye density is a critical parameter for good fringe recording, specially onto master, so decreasing it you got a more bright hologram (?).

Cristiano_Perrucci · Post by **Cristiano_Perrucci** » Tue Apr 24, 2007 6:17 am

Sergio wrote: I know now that the MB dye density is a critical parameter for good fringe recording, specially onto master, so decreasing it you got a more bright hologram (?).

Sergio,

if you decrease too much MB conc., emulsion loose it's sensitivity.

Brightness, final color replay and sensitivivity are a trade-off between a number of parameters as:

-TMG concentration

-emulsion thickness

-develop bath (warm water)

-MB concentration

-IPA bath concentration and its temperature

and, last but not least, humidity trapped into the emulsion during exposure plays an important role in this game.

A good ready to use material is quite thin (~10um) with its RH between 50 and 60%. A so made emulsion appears hard, smooth and dry if touched with a bare finger. Sticky and/or thiker gelatines will show unpredictable behaviour for long time exposure (say 10+ minutes). Moreover thicker emulsion (>20+um) is quite hard to develop in depth resulting in foggy holo. On the other hand thiner (<5um) emulsion easy randomly replays at shorter wavelenght in the green/blue region

A MBDCG master that don't replay at exactly the laser source frequency, will show nasty random black areas that will desappear changing the laser angle of incidence by a few degrees. Unfortunally a so made hologram cannot be used as a master due to its narrow field of view.

I think a good MBDCGer is closet to an alchemist rather than a holgrapher.

Cheers,

Cris

glajciorz · Post by **glajciorz** » Tue Apr 24, 2007 10:44 am

Nice

What were exposure and processing parameters Alchemist ?

I guess something like 20 mins, 30mW He-Ne ?

Will you provide short movie, like with previous 20x20cm holo ?

greetings

Adam

Cristiano_Perrucci · Post by **Cristiano_Perrucci** » Tue Apr 24, 2007 11:20 am

glajciorz wrote:What were exposure and processing parameters Alchemist ?
I guess something like 20 mins, 30mW He-Ne ?
Will you provide short movie, like with previous 20x20cm holo ?

greetings
Adam

Exposure was 18 mins for both H1 and H2

Processed in warm water @ 25 celsius for 30secs

several IPA baths form 85 to 100% @ room temp

HeNe Laser Pout=19 mW after spatial filter

Movie of this holo is available here (~1.6Mb):

http://digilander.iol.it/crispers/arpa.mpg

Note that the holo in this movie is another clone of H1 (sold to the owner of the musical instruments models) with a light green patch in the centre and a bit more dim than the one posted above.

Cristiano

JohnFP · Post by **JohnFP** » Tue Apr 24, 2007 1:40 pm

Cristiano, buonissimo!!!

I too have seen those variables come into play when I make H1 reflections in plain DCG.

What I have found is it is easier to make a broadband H1 instead of a wavelength matching narrow band H1. Then it does not have those disappearing spots when illuminated with the laser.

Keep up the great work.

John

dave battin · Post by **dave battin** » Tue Apr 24, 2007 3:48 pm

JohnFP wrote:What I have found is it is easier to make a broadband H1 instead of a wavelength matching narrow band H1. Then it does not have those disappearing spots when illuminated with the laser.

While this method will work, it will dramatically bring up your noise level

and cause the need for longer exposures to bring up the overall brightness. When im making a master hologram (H1) in dcg, its Very important to try to suppress the noise level. I know that I’ve made a good master hologram when im making a H2copy and my exposure time is half what it took to make the original master ....

When making a broadband dcg hologram its better to have a thinner emulsion 12 microns or less (allows for a better dispersion of spectra)

and on the other hand a thicker emulsion will give your hologram a better chance of being narrowband ,which allows for a better light trap,(to only reflect one color at a time)................

keep up the great work Criss ! your buddy Lazy Dog ! Whoof Whoof

can you tell us how you dry your plates?

JohnFP · Post by **JohnFP** » Tue Apr 24, 2007 4:27 pm

Dave, your points are well recongnized but my statement was that it is EASIER and very possible to make a broadband H1 and not have the missing parts when illuminated with the laser. Broadband does not have to be a white hologram but a 20 or 30 nm swing works quite well and does not increase signficantly the noise in the H2 due to the nature of DCG itself.

I guess narrowband and broadband need to be defined. 1nm? 25nm? 300nm?