Viewing Your Hologram
It's time to take a look at your hologram. Remember, the film must be completely dry to see the image. If it's still wet or damp, you probably won't be able to see anything.
The hologram we made is a white light reflection. As thename implies it is viewable in white light. The best type of illumination for this hologram is a point light source, the sun being a perfect example.
Tungsten Halogen lamps are an excellent light source. Incandescent lamps can be used, but the image quality isn't as good. When using a incandescent lamp, notice if you increase the distance of the hologram from the bulb, the image appears sharper. This happens because the lamp becomes more like a point light source as the distance increases.
To improve the quality of the playback image, put a black sheet of paper behind the hologram. To make this effect permanent, spray paint the back of the hologram black. Do this only with reflection holograms you want to display because once it's painted, you can't use it to make copy holograms.
Real and Virtual Images
There are two types of images we can view with our white light reflection hologram, real and virtual. The most common example of a virtual image is the image that is reflected in a mirror, (see figure 12). To the observer, the reflected rays that appear to come from the virtual image do not actually pass through the image. For this reason, the image is said to be virtual.
The parallax and perspective of the virtual image in a hologram is observed to be correct. As you move your head from side to side or up and down, the three dimensional scene changes in proper perspective as if you were observing the real physical scene, see figure 12. The virtual image is said to be an orthoscopic image, meaning true image.
In contrast to the virtual image is the real image. The real image in our reflection hologram can be observed simply by flipping the hologram around. The real image has some peculiar properties. The perspective is reversed. Parts of the image that should appear in the rear are instead in the front and vice versa. If you move your head to the right, the image appears to rotate in proportion to your movement and you see more of the left side, not the right side. The brain perceives thisparadoxical visual information causing the image to swing around. The real image is said to be pseudoscopic, meaning a false image.The real image is useful when you want to make copies of holograms. Making copy holograms is something we will not pursue in this short article.