vocabulary

[Ed Wesly]

I may have made the Telephone with Magnifier if it came from Integraf vintage 1982 to 1992. The phone number you can read was TJ's so you could place an order for more.

The problem with using lenses in holography is inherent in their magnification properties; magnification in the z-axis is the product of magnification in the x an y-axes. Magnifying an object will change its shape. That is why reduced-sized holographic portraits never took off, the faces became flatter as they got smaller. So it depends on how much shape-shifitng you are willing to tolerate in you final image.

Depends on where you put the lens as to whether dust would be noticeable in the final hologram. If it's in the scene like in Telephone with Magnifier it probably won't be noticeable.

A somewhat popular set up in the past, the "One-Step Image Plane Hologram", used a large lens, bigger than the object, to project the real image of the object, placed 2 focal lengths away, onto a holographic plate, placed 2 focal lengths away from the lens on the other side, for 1:1 imaging, where its wavefront collided with a reference beam for either reflection or transmission mode recording. You can get a nice image plane hologram without the H1-H2 complications, however a lot of object light is wasted because it misses the input aperture of the lens so exposure times are long, unless you use some low f/# lenses.

As always, play with the light!

[Brian]

Yes, late 80s, early 90s is the time period I saw telephone with magnifier. Nice to know who made it!

All good information, thank you. I will play, I promise.

[Din]

Anyways, I was thinking about the magnifying glass and using it to increase the size of small things in a reflection hologram. What unintended consequences may result from trying to use a magnifying glass in this way? Any peculiar HOE effects, like with a mirror? And if the magnifying glass has a piece of dust on it, will the dust show up as concentric rings in the hologram image?

It depends on how you light it. Remember always that the hologram "traps" the wavefunction it "sees". So, if the object is lit, but not the lens, in such a manner that the light reflecting off the object goes through the lens, creating a new wavefunction - the wavefunction of the magnified (well, maybe minified) object is what's recorded. Clearly, the aperture of the lens and/or the size of the plate determine the parallax. So, illuminate a real object/model, place a lens between it and your eyes, and what you see is what the plate "sees", within the limitation of lens aperture and plate dimension.

If you illuminate the object through the lens - that is, you light the object with light that's passed through the lens - then there will be a reflection from the front face of the lens, which will give an HOE. The precise characteristics of the HOE will depend on various factors such as the f# of the lens, it's curvature etc, but in all probability you'll get a highly distorted lens effect. Now, the light goes through the lens and reflects off the back surface of the lens. This too will be recorded and create a HOE, whose function will be determined by whatever the wavefunction is when it's reflected off the back surface, and phase altered by the front surface before hitting the plate. In addition, the light that's actually hit the object will also pass through the lens, magnifying (or minifying) the object wavefunction. When you illuminate this, you'll get dispersions due to the various front- and back-surface reflections off the lens, as well as the actual thing you wanted - a magnified (or minified) version of the object. In other words, the object, whose dimensions are appropriately altered by the lens function, will be surrounded by a swath of colours.

If, while you illuminate the object, manage to "clip" the lens, so that most of the light hits the object alone, but there's some "edge effects" of the edge of the beam hitting the lens, you'll get all the above, depending on the amount of "clipping", as well as some vignetting, due to the fact that light hitting the object at it's edges will be swamped by the "edge reflections" of your inadvertently hitting the edge of the lens.

In the words of Tom Lehrer, "These are all the effects that I have now disc-a-a-a-vered, there may be many others, but they haven't reached H-a-a-rvard"

[Brian]

If you illuminate the object through the lens - that is, you light the object with light that's passed through the lens - then...

In the words of Tom Lehrer, "These are all the effects that I have now disc-a-a-a-vered, there may be many others, but they haven't reached H-a-a-rvard"

Okay, now I've got to see these interesting effects. May not result in much of a display hologram, but one must explore.

[Brian]

Okay, making a Denisyuk hologram with ref beam coming at low angle straight at, and through, the plate. But in a new arrangement, I get a strange result... the image (if you can call it that) only appears if the recon light illuminates the plate from the side. A little detective work... following the recon path in the experiment setup... I locate a steel post where a little stray light reflects into the plate. Now I know this relatively weak beam interfering with the reference and reflecting beams is what leads to a poor image. But how does this weak beam completely shift the interference so much that any image at all occurs only when the recon path matches this weak beam path, and nothing at all appears when recon is along the much more intense reference direction?

And since this is vocabulary, what is the word that describes the blocking of these stray lights, and the blocking material (in my case, strategically placed thick black cardboard).

[holomaker]

Hello Brian, this is called " carding off" , it is an extremely important step in the difference of a high-quality and a low-quality hologram , By placing a white plate in your plate holder and block off each beam and check for straight light hitting that white card. This is not such an easy task as I think you're learning ! I also use the naked eye to view up stream into the reference to see that it is purely a point source and there are no stray reflections. I simply have pieces of heavy black card stock stuck into small wood blocks with slots on the top , and I never seem to have enough of them !

[Din]

I also use the naked eye to view up stream into the reference to see that it is purely a point source and there are no stray reflections.

When I do this, Joy gets mad at me!

But how does this weak beam completely shift the interference so much that any image at all occurs only when the recon path matches this weak beam path, and nothing at all appears when recon is along the much more intense reference direction?

Possibly because you got a better ratio with the spurious scattered light.

[Brian]

Thanks Dave. Indeed, tracking down unwanted light is an adventure. Fortunately I have a lot of these lying around in a drawer, doing nothing. So now they have a new use, holding card stock upright.

Possibly because you got a better ratio with the spurious scattered light.

Yes, must remember that the cross-terms make the hologram, not individual intensities.

[lobaz]

But how does this weak beam completely shift the interference so much that any image at all occurs only when the recon path matches this weak beam path, and nothing at all appears when recon is along the much more intense reference direction?

Do you still make **single beam** holograms, Brian? I would expect this strange effect in a split beam setup. If the reference beam moves during the exposure, no hologram appears, of course. However, if some weak reflection from e.g. a steel post did not move, it could make an alternative reference beam.

[Brian]

Yes, Petr, still making single beam holograms. And not making many of those. But equipment upgrades are under way.

Put together a spatial filter today. As I moved objective toward pinhole I saw... rings, brighter rings, then wonky stuff, then across one very short space there is a large patch of somewhat uniform light, then more wonky patterns, and then back to rings. So I think it is close, but needs a bit more tweaking. Maybe at end of week I'll get to play some more.