To parallel freeview images, stare at the image pair so your eyes’ lines of sight are roughly parallel. Defocus your eyes as if you are staring through the images into the far distance.
Lorgnette parallel viewers are inexpensive and are focused by adjusting your viewing distance.
Glasses using lenses magnify the image and bend the light so you can view larger images and see more detail.
A Loreo Lite 3D Viewer is made from a plastic coated cardboard with the inside surface printed black to create a collapsible dark viewing chamber. It’s prisms are designed to view 3.5 x 5 inch or 4 x 6 inch prints and 5–7 inch wide screen images. The viewing distance is 5–9 inches (12–20 cm) and it can be used with or without glasses. Courtesy of www.loreo.com
The Loreo Pixi 3D Viewer is for viewing 10–12 inch wide images. Plastic prisms in the viewer deflect the light and make it easier to fuse the images. A collapsible cardboard sleeve protects the viewer and flattens for mailing or carrying. Courtesy of www.loreo.com
The SS-1 Adjustable Stereo Wide Viewer uses adjustable mirrors so you can view large side-byside stereo pairs. Courtesy of www.3dstereo.com
The hand-held Screen-Vu is designed for parallel viewing side by side stereo images displayed on computer monitors or printed out. The mirrors are adjustable so you can view a range of image sizes. Courtesy of www.berezin.com
The Full Screen Viewer is sold as a ready to assemble kit. The cherry hardwood pieces are precision laser-cut for a perfect fit and assembly is easy. The wood parts are smooth and sanded, ready for any kind of finish you choose. To learn more, visit fullscreenviewer.com
When parallel freeviewing stereo pairs, the image for the left eye is on the left and the image for the right eye is on the right. The centers of the two images should be about 2.5 inches (6.5 cm) apart to roughly match the separation of our eyes. This limits the width of each image in the stereo pair to about 2.5 inches (6.5 cm) but this makes them easier to fuse. You can view them with your eyes aimed almost parallel or even converged a little. The smaller size of these images also makes it possible for you to freeview them on mobile devices such as smart phones and tablets. To parallel freeview larger images, with their centers farther apart than your eyes, you have to diverge your eyes, something most people find uncomfortable if they can do it at all. One thing you can do to view larger images is to increase your viewing distance so your eyes have to diverge less. If that fails, reverse the images and cross view them as described in the next section.
Image pairs for parallel viewing have the image for the left eye on the left and the image for the right eye on the right.
To parallel freeview images, stare at the image pair so your eyes' lines of sight are roughly parallel. Defocus your eyes as if you are staring through the images into the far distance—much like a vacant stare that makes everything look blurry.
If you see a second copy of the stereo pair (four images in all) concentrate on the middle two virtual images until they merge and become a single 3D image. The outer two images remain in your field of view as out of focus 2D images. If you look closely at the fused 3D image you’ll notice that you seem to be looking at the scene through a virtual window—called the stereo window
. This stereo window plays an important role in stereo photography because you can adjust it. Normally everything in the scene should appear to touch or be behind the window. Occasionally you may want an object to protrude through the window into the viewer’s space for a more dramatic, but also more problematic effect. The stereo window is discussed in more detail in sections on anaglyphs that follow.
Hints & Tips
- To remove the distraction of seeing both images with each eye, hold a stiff sheet of paper or cardboard vertically between the stereo pair you are trying to freeview.
- If the center to center distance in the images is more than 2.5 inches (6.5cm) increase your viewing distance so your eyes don’t have to diverge as much. If displaying the images on a monitor, reduce their size to get the desired center-to-center distance.
- If you see only the original stereo pair you may be trying too hard so consciously relax your eyes and try again at various distances.
- If you first see two stereo pairs you are more than halfway there. Try to defocus more and concentrate harder on the imaginary point behind the virtual pair of images until they merge into a single 3D image.
- Look over the top of the images, staring at some object in the background as the stereo pair remains in your field of view but out of focus. Slowly move your head forward and back until the third virtual image appears then lower your head so it is in the center of your field of view. If the image is blurry relaxing your eyes should bring it into focus.
- With your face close to the images slowly increase your viewing distance while staring through the images to an imaginary distant point behind them. When you see three images, concentrate on the middle one until it becomes 3D.
- Rotate your head slightly to the right or left while keeping it level.
- If you have difficulty freeviewing stereo pairs, there are a number of viewing devices discussed later in this section that might make it easier.
Here the same stereo pair has been reproduced at two different sizes with center-to-center distances of 2.5 and 3 inches. Start by trying to parallel view the smaller pair since it has a center to center distance most similar to your eyes. If you can successfully fuse this pair, without changing the way you are
viewing move your eyes to the larger pair and see if you can fuse it. Which pair is easiest to fuse?
While images are fused you can move your eyes around the virtual 3D scene to examine details. Try fusing this stereo pair
and then view each of the numbered tabs in 3D. This stereocard is from “The Keystone Eye Comfort and Depth-Perception Series”.
Modern Parallel Viewers
There are a number of modern side-by-side parallel viewers on the market, all based in some respects on the original Brewster or Holmes viewers that use mirrors, prisms or lenses to make it easier to fuse the images. To find more then we have featured here just search the Web for "stereoscope" or "stereo viewer." Unlike the Holmes viewers that view only standardized 7 inch (18 cm) wide stereocards, these viewers cover a range of image sizes. Keep in mind that when using them to view side-by-side pairs on a computer monitor or other display you can reduce or enlarge the images to the desired size.
Optical viewers for parallel stereo pairs come in three varieties— with lenses, mirrors, and prisms, sometimes used in
- Lenses have a fixed focal length so can only be used at a fixed distance from the images (although some glasses come in a variety of diopters) This means they can only view stereo pairs of a fixed size. Their advantage is that the lenses change the focus point of the image to a virtual distance at infinity so the eyes are almost parallel and can view them more comfortably. The images are also magnified to give a wider field of view and reveal more detail.
- Mirrors have no focal length so can be used to view any size images at any distance. To view images of different sizes you just adjust your viewing distance and then adjust the angle of the mirrors to converge the stereo pair. For best results the mirrors should be made of glass with the mirror on the front surface to reduce distortion.
- Prisms diffract the light so you can view images of any size just by changing the prism’s angles. Normally shallow angle prisms are used for each eye, with the thin edge in.
A Pokescope contains prisms so you can view stereo pairs of any size. It can be used to view images on the computer monitor as well as traditional stereo cards or other side-by-side prints. Made from durable ABS plastic, it folds into a 2" x 2" x 1.3" protective shape which easily fits into a pocket. Courtesy of www.pokescope.com
The jpsVisor parallel viewer uses optical glass front surface mirrors so you can view images of almost any size. Courtesy of tyrell-innovations-usa.com
The jpsHolmes parallel glasses let you view prints, picture frames, monitors and TV Sets. They allow you to adjust the distance between the two lenses to better match the distance between your eyes. Courtesy of tyrell-innovations-usa.com
The Glascope sold on e-bay has adjustable prisms for parallel viewing side by side stereo images displayed on computer monitors or printed out. A knob adjusts the prisms to the width of your eyes. To find these glasses search eBay for Glascope.