美國公司Honeywell公司於1975年申請「Distance Determining and Automatic Focusing Apparatus」（US3,958,117，1976年核准），此案利用主鏡片形成主要影像，用以控制鏡頭馬達，調整鏡片位置，再利用光感測器產生偵測影像，經過反複比對、操作調整影像計算被攝物的距離，藉以得出鏡頭最後的位置，也就是有準確焦距而能拍攝出較佳影像的位置
參考下圖顯示的自動對焦原理，主要是利用兩組光線感測器分別接收光線，找出清楚對焦的狀態。運作上，由被攝物反射的光線由光圈163進入，經反光鏡164反射，射到棱鏡162，經鏡片160打到影像感測器4，產生第一輔助影像；另一方面，同時由光圈165進入的光線，經可調整的反光鏡166，同樣射到棱鏡162，經鏡片161打到影像感測器5，產生第二輔助影像
上述可調整的反光鏡166則是自動對焦的主要特徵，透過反光鏡166的旋轉調整，影像感測器5感測的影像亦隨之變動，利用後端的電路量測兩個輔助影像的差異，在差異最小時，也就是得到被攝物距離的時候
所謂後端處理的電路與此自動對焦系統可參考下圖：
利用訊號處理器，經訊號放大、正反器等電路，最後控制馬達34調整鏡頭位置
該案主要範圍：
1. Apparatus for providing a measure of the distance between the apparatus and an object, comprising:
a plurality of radiation responsive elements divided into two similar detector arrays, each of said elements being arranged to provide an electrical signal representative of the intensity of radiation impinging thereon,
first auxiliary optical means defining a first optical path for radiation from the object and for forming a first detection image thereof on solely one of said arrays,
second auxiliary optical means defining a second optical path for radiation from the object and for forming a second detection image thereof on solely the other of said arrays, the positions and radiation distributions of said detection images on the corresponding arrays changing with changes in the relative positions of said auxiliary means and said arrays, and with changes in the object distance, there being for each such distance a one of the last-mentioned positions at which there is best correspondence of said distribution on said arrays,
scanning means for relatively moving at least a portion of at least one of said auxiliary means and the corresponding one of said arrays progressively through a predetermined range of relative positions during each of continuously repeated time periods, said range including said one position at which there is said best correspondence of said distributions on said arrays for the existing object distance,
signal processing means connected to said elements for comparing the signal from each of said elements of one of said arrays with the signal from the positionally corresponding one of said elements of the other of said arrays, and for summing the results of such comparisons to provide an output signal which exhibits a predetermined effect when said best correspondence of said distributions on said arrays is obtained during each of said periods, and
responsive means coupled to said signal processing means and said scanning means, and responsive to said effect and to said relative moving of said auxiliary means and said arrays to provide a measure of the relative position of said auxiliary means and said arrays at which said effect is produced during each of said periods, the last-mentioned measure being a measure of said object distance.
其實在此之前已經有自動對焦的技術，只是未有能夠內嵌於相機內的模組。同年，Honeywell公司再於申請專利「support for components of an automatic focusing system」（US4,020,496，1977年獲准），其揭露安裝自動對焦系統的支撐架，此案則明顯將自動對焦系統安裝於一個結構中，其中應用前案US3,958,117的自動對焦技術
這個美國的技術，在日本發展，讓日本在相機世界領先到現在，甚至到數位時代。號稱世界第一台量產的自動相機Konica C35 AF，其中即使用了Honeywell的自動對焦系統
Ron
參考資料：
http://www.digital.idv.tw/DIGITAL/Classroom/MROH-CLASS/Oh32/index-oh32.htm
http://www.camerapedia.org/wiki/Konica_C35_AF
http://www.flickr.com/photos/captkodak/284258283/
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