Wood Grain Effects on Colourholographic BB Plates
Posted: Sun Oct 10, 2010 3:08 pm
Hi Jem, I’ve just spent two days experimenting with your Colourholographic BB plates. We may be getting there slowly but I'm not happy with the results so far
Having seen from their web site that the apparent sensitivity of your plates is only 1/10th of the old AGFA film I use, I so I was not surprised when giving an exposure of 1 minute 15 seconds (the exposure I gave the old AGFA film Temp Laminated on to glass) and developing with CW C2 followed by an EDTA bleach, the film was clearly very underexposed, I noticed heavy wood graining in the plane of the film and I believed it due to the reference beam hitting the edge of the glass. The image formed was rather dim
For the next plate I increased the development time to 2 1/2 minutes with the same chemical processing. The film plate was still under exposed but not as bad and with such a long exposure I believed the wood grain effect was in fact a temperature based movement - I don't now think that
For the third plate I decided to use a special fast developer similar to Zip1 that I used to use in my early days of holography at a temperature of 34 degrees centigrade (Mike Burridge’s recipe) followed by the dichromate bleach. I sensitised and swelled the plate with 5% TEA and with a 1 minute exposure; the plate went almost black after 10 seconds development. (I had washed out the TEA before development). The image is moderately bright but with this severe wood grain effect in the plane of the plate. Please see the photograph in this link
which you will understand was difficult to take but it does show the problem. Looking at the green image, produced with a white light reconstruction beam, suggests that the ‘Sea Shell’ may re-construct brighter in green light than in red HeNe light.
Thinking about this wood grain effect immediately suggests incorrect polarisation of the HeNe – but it’s the same set-up I use regularly with my old AGFA film temporarily laminated on to glass and no wood grain effect at all
In the past I have had wood grain type effects when sandwiching film between glass plates but here there is no sandwiching at all and in my last attempt I shaded the age of the plate on both sides to prevent internal reflection effects I have experienced before.
I don't want to waste any more of your plates, but I found a box of AGFA plates I had forgotten about and will continue my studies with these when I find an answer to this 'brushed silk' type wood grain effect.
A sure-fire way of checking whether it is an ‘s’ ‘p’ polarisation problem is to make one more image on my old AGFA plates and if I get the same wood grain effect turn my HeNe through 90 deg. and see if the problem disappears … it’s a bit difficult physically as the 33mW laser is within a square section housing and the feet are not adjustable
BRgds
John
John
Having seen from their web site that the apparent sensitivity of your plates is only 1/10th of the old AGFA film I use, I so I was not surprised when giving an exposure of 1 minute 15 seconds (the exposure I gave the old AGFA film Temp Laminated on to glass) and developing with CW C2 followed by an EDTA bleach, the film was clearly very underexposed, I noticed heavy wood graining in the plane of the film and I believed it due to the reference beam hitting the edge of the glass. The image formed was rather dim
For the next plate I increased the development time to 2 1/2 minutes with the same chemical processing. The film plate was still under exposed but not as bad and with such a long exposure I believed the wood grain effect was in fact a temperature based movement - I don't now think that
For the third plate I decided to use a special fast developer similar to Zip1 that I used to use in my early days of holography at a temperature of 34 degrees centigrade (Mike Burridge’s recipe) followed by the dichromate bleach. I sensitised and swelled the plate with 5% TEA and with a 1 minute exposure; the plate went almost black after 10 seconds development. (I had washed out the TEA before development). The image is moderately bright but with this severe wood grain effect in the plane of the plate. Please see the photograph in this link
which you will understand was difficult to take but it does show the problem. Looking at the green image, produced with a white light reconstruction beam, suggests that the ‘Sea Shell’ may re-construct brighter in green light than in red HeNe light.
Thinking about this wood grain effect immediately suggests incorrect polarisation of the HeNe – but it’s the same set-up I use regularly with my old AGFA film temporarily laminated on to glass and no wood grain effect at all
In the past I have had wood grain type effects when sandwiching film between glass plates but here there is no sandwiching at all and in my last attempt I shaded the age of the plate on both sides to prevent internal reflection effects I have experienced before.
I don't want to waste any more of your plates, but I found a box of AGFA plates I had forgotten about and will continue my studies with these when I find an answer to this 'brushed silk' type wood grain effect.
A sure-fire way of checking whether it is an ‘s’ ‘p’ polarisation problem is to make one more image on my old AGFA plates and if I get the same wood grain effect turn my HeNe through 90 deg. and see if the problem disappears … it’s a bit difficult physically as the 33mW laser is within a square section housing and the feet are not adjustable
BRgds
John
John