window-effect is reached. Lift out the slide with the strips in place, and mark. Replace the strips with mounting tape. With this method, you may adjust any slide's window effect, if necessary. You will find that window-effect masking matched to your main subject distance yields more interest, and makes for easy viewing.


CHAPTER 19 / HYPER STEREO (FAR DISTANCE)

The further you look into the distance, the less plastic is the stereo scene, and at very great distances the background appears as a flat curtain. If you take a distant mountain stereo with only the normal lens separation, the mountain will appear as a painted backdrop. This is due to the fact that the distant triangulation of your lenses, which are 70mm apart, is so small that it becomes a negligible angle for far horizon distances.

However, there are ways to use your stereo camera so that you will be able to see depth even at such distances. In order to do this, you must increase the triangulation by taking two separate exposures with a greater separation (extended base). A lens cap is placed over one lens for the first exposure, then the cap is shifted to the other lens for the second (extended) exposure of the stereo pair.

Long (far) distance stereos may be taken by either of the following methods.

1. Use the stereo shift bar and calculate your lens separation to 1/50 the lens to principal subject distance. If your subject is at 25 feet, then your lens shift between exposures must be such that each view is taken with a
separation 6 inches apart.(
25
__
50
=½' or 6").
Remember that if the camera is used on a shift stand, you must move each lens to a separate position between exposures. Use an index mark so that you don't add the normal lens separation of 70mm to the camera shift and so produce too long a base. There have been stereos recorded which have been made millions of miles apart, but for preliminary practical purposes, a 6- or 12-inch stereo bar will prove sufficient. Remember that, as you increase your base sepa-

ration, you are moving your depth reception further and further back into space. Try a number of hyper-stereos. Their effect will be of great interest to you.

2. A second method to produce hyper-stereo utilizes the number 0 Stereo Angle Lens. This lens has no positive power—it is a simple prism. If you place the lenses in the standard Series V filter mount so that the black lines are facing inward and the red lines out, to take your picture, you will find that you have increased your separating distance (triangulation) and this additional triangulation will give you long distance or hyper-stereo. This second method is simple for the beginner because no extra shift bars are necessary and the results are excellent. Besides, both pictures are taken simultaneously so that you don't have to remember to take two separate views or manipulate the camera excessively.

Hyper-stereos are indeed novel, but they have many shortcomings which limit their usefulness. They are unnatural in that your distant subjects appear as small miniatures of in full-size proportions. Because of this unnaturalness, viewing is tiring and after a while they become visually unacceptable.

Take one or two hyper-stereos as a technical exercise, only. You may not understand what a hyper-stereo actually is until you have viewed one taken with an extended base as contrasted with a regular stereo shot of the same scene.

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