Modern Classic SLR Series
Canon A-1 - Other Issues Part VIII

 
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The Canon A-1 and many of the SLR models made by Canon are heavily electronic (and battery) dependent in their design. These are facts that can made a user very comfortable and uncomfortable. The comforting part is, because less mistakes can be occured along the way with the assurance and convenience of automation. The negative aspect is, of cause, the heavy reliance of battery power to operate the camera but since it is almost quite natural for a Canon user to get used to such 'product characteristic' of a Canon electronic SLR

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A programming operational flow chart of the Canon A-1

(The only two SLR camera bodies that can work mechanically are both professional class bodies in the Canon F-1 in 1971 and New Canon F-1 in 1982 - the latter can work both electronically as well as mechanically). Compared with the earlier fully electronic Canon AE-1 body, the Canon A-1 featured here has some 20 original technologies used, not only in the camera itself but in the whole designing, processing, assembly and inspection process as well.

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Credit: Images courtesy of Mr. Claudio®. who is a collector for Canon photo gear, he also has an Ebay Section as well as maintaining a website on his own where occasionally trading some photo equipment. Image(s) copyright © 2003. All rights reserved. Please respect the visual property of the contributing photographer.

Although when compared with today's high tech SLR cameras, the electronic used is still considered in a raw form during the boom of AE SLRs days of the late '70 and early '80, but since those days the SLR market was still very much occupied by hard-core mechanical camera users, an electronic SLR must be designed with sage usage and made to last. The use of computers in this case, utmost in precision is assured for the A-1, from its internal mechanism that comprises five main modular units and 31 sub-units, to its many photographic functions. Central to the A-1's operation is a microcomputer. This device was first used in the Canon AE-1 with great sucess commercially.

The processing power of its micro-computer in the Canon AE-1 of 1976 was, however, a bit limited. In order for the A-1 to perform all the camera AE functions it does, a more powerful micro-computer is utilized for the A-1. This one has a processing power two or three times that of the simpler task AE-1 - a feat accomplished by changing all incoming data into pulse-controlled digital form. And since the least disorder in input could affect the whole operation a Gray code has been installed to make sure inputs such as shutter speed, lens speed and film speed are exact. Following are explanations of some of the technologies that make the A-1 a electronic marvel it was in the late seventies and even highly respected during the early part of the '80

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The use of Pure To really understand what this recent electronics development is and what makes it so important, let us trace its roots.

First of all, some mention of the IC, or integrated circuit, is in order. The IC is basically a collection of electronic parts that have been brought together into a single unit. It also stands for the smallest scale on which these parts can be miniaturized. However, an IC's limitation as to the amount of elements it can contain meant that its use in cameras would soon be improved upon by newer technology. This came in the form of Large Scale Integration, or LSI, that could integrate about 400 elements.

The circuitry used in the Canon AE-1 actually went one step further than even this by employing or Integrated Injection Logic, the number of elements integrated being equivalent to an LSI of over 1,000 parts. Since this took the place of three conventional units, only one-third the space was necessary. Thus, the compactness of the A-1.

Obviously, to get a camera that has more functions than the AE-1, but in a size not much bigger, still more advanced technology was required. Enter Pure . This is only one of the integrated logics the A-1 employs. Equivalent to over 300 pieces of regular IC, a single piece of Pure L enables three to four times the integration possible in the AE-1. In all, a total of five ICs are woven into the A-1's circuitry. One regular IC is sealed into a single package with the SPC and is a part of the BI-MOS logarithmic amplifier's construction.

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Another IC, this one an , is used for information input. With an internal layer of insulation, this isolated is located on the same chip as the analog and digital circuits and dual ramp analog-to-digital converter.

Thirdly is the data processing center or CPU. This is where the Pure is used in an LSI. Greater density, and thus greater power is achieved because only digital circuitry is employed. Then there is a bipolar IC consisting of an oscillator, magnet and driver for LED activation. Last of the ICs is an LSI with an isolated that is used in the decoder driver section. An LED driver is built in here, too, for further savings m electricity consumption.

Programmable logic array All the information that has been input into the Pure I2 L is sequentially programmed according to functional order. The unit that performs this task is composed of programmable logic array (PLA). By a series of yes/no questions, the PLA decides which mode has been selected. Then, on the basis of input information, it picks one of 40 programs and sends out the chosen program to the digital calculator for calculation. Use of the PLA is what made the AE Mode Selector/AT Dial combination possible.

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Dual ramp integration analog-to-digital converter The only piece of information that cannot be turned immediately into digital form is the subject's brightness, which is originally in analog form. For digital conversion, a dual ramp integration analog-to-digital converter is used, the first time that such a device has been used in a camera. Its advantage lies in the fact that it is unaffected by temperature and humidity changes. And since 80 to 90 percent of all digital voltmeters employ this converter, you know that it must be perfectly accurate as well.

Bus line system Just as many buses can travel on the same road according to the same time schedule, this system enables a lot of information to be transmitted over one line. Normally, all the information pouring into the A-1 would require one line per one piece of information. However, the A-1 uses, for the first time again, the bus line system. Based on the time sharing system used in computers, it is divided into two main lines: the"l Bus"for inputting information into the built-in micro-computer and the "O Bus" for transmitting values computed by this computer to the decode driver.

Ultra smooth flush Plate Flush is the process by which chatter is
eliminated from the A-1's circuitry. For aperture control, f-numbers are digitally detected after the number of ON/OFF signal pulses are counted. If chatter was present during this process, a mistaken count would result.

Chatter is caused by a combination of two things: a micro slide brush and deterioration in smoothness of an ordinarily used copper foil print board. This brush moves over the segmented aperture value electrode plate at a high speed. If the usual 35
u print board is used, deterioration in smoothness will result and chatter will arise. To prevent this, the segmented aperture value electrode plate pattern is formed on a 23u thick copper foil plated board that is given a tetron/epoxy coating. This board is then heated and pressed to ensure a smoothness to within 5u.

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Dynamic display All exposure information is displayed in the viewfinder in red LEDs after going through the decoder driver.

The method of indication used is the dynamic display method as opposed to the static display method used in other cameras. The value of this system lies in the fact that only one decoder driver and one multiplexer are needed, no matter what the number of digits. Such is not the case with the static method. In this latter system, a counter and a decoder are needed for each digit displayed. Thus the dynamic system reduces the number of wires and components necessary, as well as saving on power consumption and being more efficient.

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Micro-patterned two-side flexible substrate The substrate used for the A-1's electronic circuitry is a flexible board that greatly rationalizes wiring and increases reliability.

Mounting density with this board is very high as it is of multilayer construction with patterns on both sides. Minimum distance between lines and line width are both 0.2mm, close to the limit obtainable by present technology.

Diode chip-on-board Chip-on-board is the method by which six common four-cathode diode chips are directly bonded onto the circuit board. In order to rationalize wiring and meet circuitry conditions, a diode for signal separation becomes necessary for each digital switch input. In the A-1, 20 such diodes are needed. If conventional glasssealed diodes were used, the camera would have to be much bigger for them all to fit. Thus employment of the chip-onboard method. This technique has been used for LEDs before (and is also used in the A-1 for this purpose) but this is the first time it has ever been used for diode array.
Info above was contributed by: Canon Logo.gif
(Credit: Technical Team, Canon Marketing)





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