For what seems like forever now, I’ve been working on developing a DCG process for myself that I could use when making white-light copies of my silver masters.
After some inconsistent results I stripped the table top of all components and set up an interferometer to see how stable the table was.
For almost two months now, I’ve been working to figure out the exposure and processing steps to use in order to get bright and clean transmission holograms using my Coherent 315M and VRP-M film.
After blowing through roughly 68 pieces of film (mostly 1.5×1" in size) I think I’ve finally nailed the process to use for transmission masters.
JohnK on the holography forum had asked if I’d experienced any problems with delayed development of VRP-M.Â He’s been working on making holograms using a Coherent 315 and VRP-M film and was wondering VRP-M was sensitive to delays of several hours between exposure and development.
I normally develop right after exposure but did the following test to find out how VRP-M behaves.
I don’t know how often I’ll do these but I had the urge to record what I was doing in the lab.
I’ve been trying to get good results with the coherent 315 laser and VRP-M film and haven’t had any luck. In each case where I’ve gotten any kind of image, it’s been extremely dim.
Unfortunately I found that my shutter was causing a full seconds worth of ringing in the table and had to build a new shutter. That was completed yesterday and this morning I’m doing some more exposure and development tests.
My apologies for the sound quality. Next time I’ll have to make sure the microphone is closer to me at all times.
Without further ado, here’s my labcast.
Let me know if you’d like me to do more of these.
Well, it turns out that one of the problems I was having with my green laser and the VRP-M film is my shutter.
When it opened it set the table to ringing for at least a full second.Â My 2-4 second exposures were incredibly dim because they were getting fogged for the first second.Â I found this out after setting up an interferometer (shown above, click for a larger picture) opening and closing the shutter while it was going.Â The fringes really moved when the shutter closed but as no light would have been reaching the film, I didn’t care about that.Â Have it shake the table when opening was a problem though.
I tried all sorts of things to improve the isolation of the shutter and damp the vibrations it was putting out but in the end I had to give up and make a shutter from scratch.
I took a panel meter and attached a multi-layered piece of aluminum foil and used that reflect the incoming beam and create a beam dump on the inner surface of the meter housing.Â Painting the whole thing black created a nice little box to keep the beam in.
After putting a couple of beads of silicone where the meter arm rests against the coil I ended up with a nice quiet shutter that didn’t disturb the fringes at all.
It’s being put through its first hologram-making test right now.
Laser Focus World is reporting that researchers at New South Wales University have developed a holographic astigmatism test that’s faster to use than the lens-flipping "how does the chart look now?" test we’ve all endured when having our eyes checked.
The current method of looking at a distant object through a number of lenses to prescribe corrective glasses is at best cumbersome. In an alternate approach, the researchers recorded the wavefront emanating from various sunburst patterns located at different distances from the eye in a hologram. When a subject views through this hologram (illuminated by a plane wave), he or she will see the images of various sunburst patterns located at different distances from the eye.
Unfortunately there’s no additional information at the university site.Â Perhaps they’ll put something up soon.
Optics.org has a bit more information and a few extra photos available.