today's DCG

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Joe Farina
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Joined: Wed Jan 07, 2015 2:10 pm

today's DCG

Post by Joe Farina »

These are some photos of a test hologram made today. It's DCG with dyes for red and green. The exposure is a combined 532nm (~14mW) and 633nm (~20mW), and the plate is about 5 inches square, exposure time 30 minutes. This is a rough hologram: unfiltered emulsion, unfiltered beam, etc. Also, it was underexposed in the edges, and overexposed in the middle (the Gaussian beam made a patch in the middle, since the 60X objective was only 9 inches from the plate). But I'm learning a few things. I took the second photo to show the specular reflection from an irregular mirror fragment which was placed at the bottom of the two figures. I was surprised how much light the mirror throws back, like a real mirror almost. Now I know how all those high-efficiency results were obtained in the DCG literature ;)

I guess this shows how important beam ratio is. Maybe the dyes are absorbing a lot of light, and the specular reflection from behind shows how bright the reconstruction can be.
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Steven

today's DCG

Post by Steven »

Well done Joe.

It's very difficult to process DCG when you have an uneven exposure like that.
You get the hard parts that want to stay narrow band and the less exposed, soft parts that want to go broadband :-(

I have spent the past two days reprocessing a couple of holograms like that without success, I binned them in the end.
They will now serve as cover plates.

I guess that if you expand your laser beams to give a more even exposure, your exposures will be over an hour long.
Have you measured the energy density of the 532nm reference beam hitting the plate and do you have an exposure in mJ/cm² please?

I'm using exposures of between 25 and 45 minutes for normal DCG, giving me approximate exposures of between 90mJ/cm² and 220mJ/cm² , depending on what I'm shooting (beam ratios). The energy density of the ref beam in the centre of my plate is 48µW/cm².

I haven't done any recent experiments with MBDCG as I'm busy producing xmas cards in DCG.
I believe you are correct ref the dye absorbing a portion of the laser light.
Have you had chance to measure this? I would be very interested in your results.

I did a few measurements some months back using dip and shoot and a gelatin coating of about 8-9µm:
One minute dip in 3% AmDi: Transmission at 532nm = 95.4%
One minute dip in a sensitizing solution using the ratios of chemicals to H2O used in the paper by Jianhua Zhu et al: Transmission at 532nm = 93.2%
One minute dip in my own MBDCG sensitizing solution, (below): Transmission at 532nm = 67.3%
All sensitizing solutions were at ambient (about 18C).

My experimental MBDCG sensitizing solution (approximate):
H2O 600ml
Guanidine carbonate 11.2g
Potassium chromate 940mg
Rhodamine 6G 45mg (22.5ml of a 0.2% stock solution)
Boric Acid used to adjust P.H. to approx 10.1

The P.H. may not be high enough to offset the lower P.H. of the pig gelatin I'm using to coat my plates, but I will continue with my experiments next year.

Steven.
Joe Farina
Posts: 804
Joined: Wed Jan 07, 2015 2:10 pm

today's DCG

Post by Joe Farina »

Hi Steven,

Thanks for the details about your recent work.

The hologram posted was just a test, I wanted to see the effects of over and under-exposure in the same hologram. My standard exposure time is about 30 minutes, even when there is a wider beam spread on the plate. But exposure time does have an important effect with MBDCG, of course. It's also fairly easily over-exposed, and the results are typically dimmer for over-exposure as well as under-exposure.

I really should just measure beam transmission through my plates, to settle that question. Don't have energy density figures either, sorry. But the 60x objective was 9 inches from the plate, if that helps. There was quite a hot spot in the middle. By the way, my results with Type A gelatin were consistently worse, compared to Type B, in connection with MBDCG. I would suggest Type B, either hide or bone, but preferably bone.
Steven

today's DCG

Post by Steven »

Hi Joe,

I wasn't aware that over exposure was problematic with MBDCG.
I will keep this in mind when I resume my experiments.

Quick calculation, maths and optics not being my strong point though:

Plate size 5" x 5" = 12.7cm X 12.7cm
Plate diagonal = 18cm (approx)
Area of a circle with radius 9cm = 254 square centimetres.
Assume power loss through objective, say 10%.
Power input to objective (532nm) 14mW
Power output after objective = 12.6 mW
Assume top hat laser beam profile, but we know it's far from it.
12.6mW divided by area of 254 square cm = approx 49.6µWcm²
Exposure =30mins = 1800 seconds
49.6µW X 1800 = 89.28mJcm²

Depending on how much the beam has been expanded beyond the outer edge of the plate, the outer edge may be getting significantly
less than 89mJcm², maybe only 10-20mJcm². likewise, the centre of the plate will be getting much more than 89.28mJcm², possibly 200mJcm².

Yes, I think that it's a good idea to do test exposures like that, as you cover a wide exposure range in one shot :-)
Hopefully, some area of the plate will be correctly exposed.

A relatively cheap and effective light meter that is capable (with a few extra components) of giving you a readout in µWcm²
can be built from the info here:http://redlum.xohp.pagesperso-orange.fr ... meter.html

If you include a few extra presets and a couple of switches in the circuit you can add a selector switch to select between 532/633 and a switch that will
allow you to point the light sensor straight up the ref beam at normal incidence, but the readout will give a reading as if it was taken at Brewster's angle.

Steven.
Joe Farina
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Joined: Wed Jan 07, 2015 2:10 pm

today's DCG

Post by Joe Farina »

Thanks Steven. Overexposing reflection MBDCG isn't very dramatic (with regards to reducing brightness), but I did a test where a few minutes extra exposure (it was a strip exposure) did noticeably reduce brightness. I have a lasercheck, and this does provide microwatts for either 532 or 633. I have the tendency to rely on rough tests, but taking a more scientific approach might be helpful.
dannybee
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Re: today's DCG

Post by dannybee »

WoW this is great Joe , what was the mix and info... the over expose looks good, it problly make it more narrow band... but wow would love to try this in my lab i have about 40mw red , then 100 green and 200 blue
Joe Farina
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Joined: Wed Jan 07, 2015 2:10 pm

Re: today's DCG

Post by Joe Farina »

Thanks Danny. This is Jeff's formula, except that it includes R6G in addition to MB. And boric acid instead of acetic to adjust the pH. I'm getting better results now with Type B (bone) from Great Lakes.
dannybee
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Re: today's DCG

Post by dannybee »

Joe i had a idea doing Lippmann images like this but use dpl projector for image source so refrence can be at a angle rather than head on
Tony DCG

Re: today's DCG

Post by Tony DCG »

Nice work Joe.
My only comment is if possible take a photo of the actual object. It's always good to see what the real colors look like.
Best of luck
Tony
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