G307 DCG woes

emf · Post by **emf** » Sun Dec 13, 2009 6:40 pm

A quick introduction -- I'm started playing around with holography this fall with one of Integraf's kits. I got a decent image on my first try, and managed to make a few reflection & transmission holograms of a few shiny objects. The results were encouraging, but dim and not really what I was hoping for. After a lot of reading on this forum and wiki and consulting my bank account, I decided to go the DCG route. After working through a bunch of stupid mistakes (like having the fridge set well below freezing), I started to get some nice holograms. Some images were brighter than others, but most of the time I'd get a hologram that clearly showed the bright parts of the subject, and maybe 1/4 of the time I'd get one where everything including the background looked good. This was with 20min @ 10mw Denisyuk-style exposures, room-temperature Kodak fixer, 70%, and 91% IPA baths, followed by a ~100 deg F 99% IPA bath.

Anyway, I wanted get the exposure times down a bit so I could try some split-beam work without hour-long exposures, so I gave G307 a try. I must have been very lucky, because my third or fourth try gave me a very nice image (attached). I've made at least 20 attempts now, and they all seem to fail in the same way: I get dim image, but I can only see a thin horizontal(ish) band at a time. I can scan this visible band up and down the hologram by tilting the plate back & forth, but there's no angle where the whole image becomes visible at the same time. I also need to aim the reconstructing beam at an angle much closer to the surface normal than the 45-ish degrees I should be using, and the holograms are usually more blue than green.

The only thing I knowingly did differently with the one plate that worked is I didn't tape up the top edge of the plate. I've tried making subsequent exposures with and without this tape, and I seem to get bad results either way.

Does anyone recognize this problem from my description, or have suggestions of which variables to play with?

My procedure: Mold-coated plates, 3"x3". 10mW C215 laser, 5 minute exposure. Baked at ~230 deg F for 3 minutes, then into 75 deg F water until clear, usually ~8 minutes. If I use 85 deg F water, it goes milky. then 1 minute in room-temperature (low 60s) 70 and 91% IPA baths for a minute each, then 99% IPA at 100 deg F for 30 sec to 2 minutes.

Thanks for any suggestions

Eric

JohnFP · Post by **JohnFP** » Mon Dec 14, 2009 12:23 pm

Hey Eric. My first guess is that something is moving or the laser is creaping but to be sure, can you post a few photos at different tilt angles so we can actually see the band you are talking about and how it behaves?

emf · Post by **emf** » Mon Dec 14, 2009 3:25 pm

I'll try to take some pictures this afternoon or evening. I haven't bothered to seal most of these failures, so I'm not sure what I have lying around.

You're right, I keep thinking this *must* be a problem with my G307 process, but I haven't really gone back and verified that all of the basics are still working. My basement has been getting steadily cooler over the past few months, I guess that could be causing my laser to act up.
When I get a new batch of plates coated, I'm thinking of doing a series of alternating G307 and plain DCG test shots. That would help me rule out all of the steps they have in common.

dave battin · Post by **dave battin** » Mon Dec 14, 2009 4:24 pm

Hi Eric , and welcome to the forum. I agree with John totally. Some pointers here, keep your set ups simple as possible (for now during your testing phase), forget trying to do split beam dcg with a 215m. the dcg is way too insensitive to use 15 mw of green. Better to make a silver master and do contact or proximity copies in dcg. one luxury john has over us, is his fast exposures using the blue light, with the 532 long exposures are expected, you need to build a total cardboard box around your one beam setup (with laser outside the box). when i was doing
5+ min exposure i would see banding/dimness from thermals, after i built the box the banding went away, The settle time need to be long too ........how long do you let your film plate settle? I have included a picture of an old test set-up jig, something you might want to try using for these long exposures, also try shooting a smaller size plate to start like a 2x2 and your exposures will be 3-4 x faster too. No spatial filter needed, a lens or concave mirror is used at a greater distance to allow the beam to "clean-up" before hitting the plate, i tested the mirrors i use, and they loose @ 10% of the light ........

Eric where do you live .............

Justin W · Post by **Justin W** » Mon Dec 14, 2009 4:39 pm

Hi Eric

I agree with John - the issue is very possibly motion.

Your description of only being able to hologram the bright parts of the object sounds all kinds of familiar; I've seen exactly that before in split beam work where I had a heavy object that was poorly mounted for exposure, as well as other times when I've not permitted enough settling time before opening the shutter.

Setting up an interferometer will be a big help in diagnosing your troubles. Try to incorporate as many of the elements involved in your camera as you possibly can, then eliminate them one at a time until your fringes stabilize. This will help you zero in on whichever may be the unstable component. If the fringes just won't stabilize, beef up your mounts from the laser on downstream until they do, and if they still don't, you may next have to improve the rigidity and/or isolation of the whole system.

Troubleshoot, troubleshoot, troubleshoot. Best of luck and big up ya chest for having the gumption to try this in the first place!

Let us know how it's going, dude.

emf · Post by **emf** » Mon Dec 14, 2009 8:10 pm

Thanks everyone for the replies. I usually allow 15 or 20 minutes settling time, and laser is turned on well before the settling period. My setup is all in the open, though, there's no box to prevent drafts. I'll throw one together for my next test.

I've done the interferometer thing to make sure my isolation table was good enough, and it looked stable over short periods of time, as long as I wasn't walking within a few feet. I guess what I really need to do is set it up again, mark the location of the fringes on the wall, and then watch it for 30 minutes or so to make sure they don't move? Sounds kind of relaxing, actually.

I'm in Blacksburg, VA.

To give you a rough idea of my setup, here are some photos from my previous test hologram. The setup for my current one is pretty much the same. Try to control your laughter =) First, there's the laser & controller, shutter, and an acrylic lens followed by an uncoated glass lens to spread the beam. What's left of the laser beam travels horizontally about 6 feet to the subject on my makeshift isolation table. The trinket is mounted upside-down on a wedge made from masonite at roughly Brewster's angle. The plate leans on the subject, touching the cat's nose. The other photos show the laser's point of view with glass plate and with a piece of white paper in place of the plate to check how even the coverage is, and the plain DCG hologram from a 20 minute exposure.

: laser, shutter, lenses; c215-10.jpg (66 KiB) Viewed 3084 times

: subject in jig in full light; cats_rule_setup_1.jpg (39.66 KiB) Viewed 3084 times

: as seen by the laser; cats_rule_setup_3.jpg (26.02 KiB) Viewed 3084 times

: white card to check laser coverage; cats_rule_setup_2.jpg (19.21 KiB) Viewed 3084 times

: the completed dust collection^H^H^H^H^H^Hhologram; cats_rule_small.jpg (38.68 KiB) Viewed 3084 times

Dutchelm05 · Post by **Dutchelm05** » Mon Dec 14, 2009 8:46 pm

Is that wood as your object holder???
If so that would be a major problem. Especially with these long long exposures
You should consider metal
As for blue and green, what is your formulation? Gel:AmDi:H2O?
Best of luck Eric

dave battin · Post by **dave battin** » Mon Dec 14, 2009 10:08 pm

this is very good effort Eric! please listen to the tips given out here as they can save you many many hours of failed tests ...
the fact you are getting blue tells me you are way over exposing ,seeing how you live in the usa why dont you start off with Kodak rapid fix as your hardener. i can almost guarantee bright results from what im seeing. you have the correct idea for the setup but your backer on the object is some type of board , this wont do. see the picture i supplied above these are three flat head bolts epoxied down onto a marble tile, settle times should be at least as long as the exposures .you can use a nice overhead projector black marker(water soluble)to black out the upper and lower edges of the film plate. The film plate is made longer than the image and will be cut off after exposure and before processing ........... good luck and make that baffle box good as you can, as you will be using it for years to come !

emf · Post by **emf** » Tue Dec 15, 2009 4:08 am

Ok, metal it is. I'll stop by the hardware store tomorrow and see what I can find. I don't know what they have in metal plates. Is 1/16" steel thick enough, assuming they carry it?

re: fixer, I do use a chemical fixer for regular DCG. I wasn't paying attention when I bought it, so I wound up with a different fixer: Kodak 197 1746. Although I have nothing to compare it to, it seems to work well, clearing the plate in 30-45 seconds. I just bake the G307 since that's what the instructions say.

My emulsion is taken straight from the wiki, 100:12:3 water:knox gelatin:KDi. At least, that's what I started with, and got nice results. I switched to mold-coating the plates with plain gelatin (100:12) at scotch magic tape thickness, then sensitizing later with 100:3 chilled water:KDi for 30 seconds then squeegeing. I believe the cat was one of the sensitized-after-coating types.

dave battin · Post by **dave battin** » Tue Dec 15, 2009 5:21 am

[quote="emf"]Ok, metal it is. I'll stop by the hardware store tomorrow and see what I can find. I don't know what they have in metal plates. Is 1/16" steel thick enough, assuming they carry it?[quote]

marble and ceramic tiles work nice as well, the 4"x4" ceramic tiles at H-depot are $.13 each .................

you will want to get the kodak rapid fix with the additive hardner.