Modern Classic SLRs Series : Canon T-90 - Built in Motor Drive

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The biggest challenge for the Canon T90 design team was to to combine ultra-high energy efficiency with a compact, lightweight body within the T90. Conventional wisdom had it that the mechanical features of an automatic camera were driven by a single, multi purpose motor. The difficulty here was that such a motor operated very inefficiently; since, for example, the amount of energy needed for film transport was different from that needed to charge the shutter. Even more problematical would be the need to power technological advances such as the 4.5 fps film transport speed and the fast 114000 sec. shutter speed. The T90 was going to need a massive motor. To give an indication, the current Nikon AF-F90x has the same built-in motor winding speed of 4.5fps, ten years later, while the top of the line Nikon, the F4s - also employ a similar three motor designs, has a top speed of 5.5 fps. The Canon's solution was: Instead of one immense motor, they would use three smaller ones. Combined. Advantages: They would be lighter in weight and would take up less space. Yet since each motor could be assigned a specific function or group of functions, operation would be more efficient. Film loading, film winding, and film rewinding are all fully automatic. The reasoning behind this approach was that too much motor power is a kind of "overkill." That is, you don't need to power the shutter when you are driving the film rewind. Various mechanical actions happen separately. Thus you don't always need a lot of power. Of course, when it is needed, it has to be available. The results of this research are easy to appreciate. Before, in order to drive the film transport mechanism at a rate of 4.5fps, and even 12 AA-size batteries were required. The T90 reaches that rate with only four battery cells to power. Each coreless motor Is highly specialized. In addition to being smaller, H is located close to the mechanism it drives to improve efficiency. Each motor also requires less energy to operate. And the overall electrical system is so well designed that Canon was even able to include the world's first two-speed automatic changeover function. The film transport drive has three power modes: high speed continuous shooting at 4.5 fps, low speed continuous shooting at 2 fps, and single frame shooting. The lower speed of 2 fps lets you space out the shots and preserve battery life. You can switch from one mode to the other easily with a single touch of the Film Winding Mode Button in the Palm Wing. When using alkaline batteries under normal shooting conditions, about 75 rolls of 24-exposure film can be shot in the HIGH mode and about twice that number is possible by choosing the LOW mode. In addition, for very cold conditions, Ni-Cd batteries which function well in low temperatures can also be used. The T90 motor drive features an innovative changeover function that automatically switches from the top speed of 4.5 fps to 2 fps whenever the battery voltage drops below a prescribed level. This extends battery life, so more pictures can be taken with the same batteries. By today's standard, these achievement may sound like stone aged technologies, but these are pioneering in the early '80 and has a strong influences in AF modern camera designs. And all these are factors portraying the T90's justification as Modern Classic SLR body.

The three motors: The one on the left handles mechanism charge motor, the center motor is the forward film transport motor, while the right hand side is the location of the Film rewind motor. The Three Motors: • 1. The forward film transport motor: A single coreless motor is dedicated to driving the film forward through the camera. Since that is its only function, it is designed to have excellent stopping and starting characteristics. Film transport is fast and efficient, no matter what the type of film or film load, and operation is uniform even under adverse temperature conditions. •2. The mechanism charge motor: The second coreless motor powers the mechanical elements involved in actually taking the picture. It drives the shutter, mirror, automatic aperture lever, AE operations, etc. This motor is located inside the hand grip and works at the same time as the film transport except during automatic film loading. It is also possible to charge the mechanism alone during multiple exposure photography. •3. The film rewind motor: The third motor is a coreless motor similar to the film transport motor. Placed near the spool it drives, it is dedicated to rewinding the film Since it is so specialized, its operating efficiency is about three times that of conventional rewind mechanisms. It begins rewind automatically after the last frame is exposed (approx. 8 sec. for 24 exposure film).

The advantage of their three motor design in the T90: • 1. Since each motor directs its functions independently, an increased degree of sequential control is possible, improving overall operation efficiency. •2. Energy conservation is maintained in all performance situations because each motor is designed for maximum efficiency within its individual functions. •3. Power transfer efficiency is improved because the motors are located close to the mechanisms they drive. •4. The H/L automatic transmission uses normal and reverse motor rotation and takes advantage of optimum gear ratios that respond to the various operating loads. Moreover, the mechanism is able to automatically convert from H mode to L mode by detecting the increase in load on the film transport caused by the decrease in film transport speed which occurs when the battery voltage becomes low.