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Passive Autofocus (Two-Array Comparison)
Norman Stauffer at Honeywell built a focus detector from two rows of tiny light sensors side by side on one chip. In his FIGURE 2 each row views the subject through its own small lens, a short distance from the other - like the two windows of a rangefinder. How far one row's picture is shifted against the other's gives the subject's distance, and the camera sets the taking lens to match, without trial and error. Compact cameras from 1977 used it; later SLRs moved the same comparison behind the taking lens itself (phase detection).
**US 4,002,899**, "Focus detecting apparatus", Stauffer, assigned to Honeywell, filed 31. October 1975, granted 11. January 1977: "radiation responsive elements formed on a single planar substrate and divided into two similar coplanar detector arrays lying immediately adjacent each other".
**You see the principle with a card**: a two-hole mask gives a lens two viewpoints, just as Stauffer's two lenses do; out of focus the point splits in two, and which spot vanishes when you cover one hole tells you which way to focus.
中级
90 minutes
说明
1
1
Make the two-hole mask
Make the two-hole mask
Cut a card disc to fit a lens holder. Punch two 3 mm holes 20 mm apart, symmetric about the centre.
此步骤所需材料：
黑卡纸1 张所需工具：
手工刀
钢直尺2
2
A point of light
A point of light
Cover the torch with foil pierced by one pin-sized hole. Put it 2 m from the bench in a dim room.
此步骤所需材料：
铝箔1 张
美纹纸胶带1 卷所需工具：
LED 检查手电
卷尺3
3
Split and join
Split and join
Mount a 100 mm convex lens with the mask right in front of it, and a tracing-paper screen behind. Slide the screen: two spots merge into one exactly at focus. Measure their separation 5 and 10 mm either side of focus.
此步骤所需材料：
凸透镜套装1 套
裁剪拓样纸卷1 张所需工具：
光学导轨与滑轨
透镜支架套装钢直尺4
4
Which way?
Which way?
With the screen too close, cover the left hole and note which spot disappears. Repeat with the screen too far. The answer flips: that is the direction signal phase detection gives for free.
5
5
Triangles and correlation
Triangles and correlation
正在加载 Jupyter 笔记本…
6
6
History & Context
History & Context
**What the patent specifies:** two similar, adjacent, coplanar arrays of radiation-sensitive elements on one substrate, whose outputs are compared to measure distance or focus. **Modern build (derived):** a Scheiner two-hole mask - two viewpoints and an image shift, made visible.
Christoph Scheiner described the two-hole experiment in 1619 to study the eye's focusing. Honeywell's chips put it into cameras; today's phones put phase-detection pixels directly into the image sensor. Its limits: it needs contrast (a blank wall defeats it) and precise alignment between the detector and the lens.
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