Additional Information on:
Canon AL-1 QF (Quick Focus) Camera - Part II

 
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The top panel of the AL-1 is very simple but well layout with its various control lever and button. It has a strong 'A-Series flavour'. Note the shutter dial only has speeds of 1/15 sec up to 1/1000 sec. plus B (Bulb). Although the camera looks metallic, its body construction was not made of metal but a special polycarbonate material that was coated with a metallic paint.

Top Panel.jpg (13k)
The use of the material also contributed to the overall compactness and lightweight. The shutter release button is threaded in the middle so you still can use cable release to lock for time exposure and macrophotography.


Inside the viewfinder, a small red arrow lights up at the base of the image. It's pointing to the right, so you immediately turn the lens focusing ring in that direction. If you have gone too far by over-twisting the direction of the focusing ring, an identical arrow, this time pointing left, appears. A slight adjustment in that direction and a bright
green spot lights up. Your subject should be in focus as indicated by the electronic focusing detector.

How does the electronic rangefinder works ? The TTL sharpness detection system uses three CCD line sensors. Focusing information is calculated by a microcomputer which then activates the LED focusing indicators in the viewfinder. Focusing with the QF system is simple. Compose the picture so that your subject covers the focus frame in the center of the viewfinder. Depress the shutter button halfway , one of the three indicators will then light up.
< indicates that the point of focus is beyond the subject and that you must turn the focusing ring to the right. Similarly it will inform you if you are focusing too close. Rotate the ring to the left. When the green O lights you know your subject is in sharp focus.

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Depress the shutter button all the way to take the picture. What if the shutter speed is too slow for a sharp picture ? The AL-1 even employs a camera shake warning index indide the viewfinder to alert you of possible blur image due to slow shutter speed setting.

Note
: The solid lines indicate the light rays focused on the actual film plane and the dotted lines indicate the light rays from the subject focused on one of the three sensors A, B or C.


Canon's Magic Patterned Mirror The QF system did include several technological innovations by Canon. One of them can be inspected by dismounting the lens. The AL-l's main mirror is inscribed with an intricate pattern of lines. These lines instead of reflecting light up to the viewfinder, allow it to pass through to a sub-mirror located just behind. The light is, in turn, reflected down to the CCD image sensors. The central area, used for the quick focus system, has a transparency of 45%.

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The reflectivity increases progressively toward the periphery. Although portion of the light is redirected for focus detection, the viewfinder image still stays reasonably bright - may be due to the employment of the improved laser matte screen. < Left: The Patterned Mirror in the AL-1 reminds me about the patterned shutter curtain used in some of the Olympus OM bodies, likewise, the more refined textured shutter curtain of the Pentax's LX.

The lines aren't completely transparent, however. To increase the brightness and ensure that the pattern won't be visible in the viewfinder they are given a thin reflective coating of aluminum. And although the pattern may look like some sort of abstract painting, its design is far from random.

This configuration produces an ideal balance between the requirements of the quick focus system and the light distribution of the viewfinder.Canon's patterned mirror provides a brighter viewfinder than the half mirror system utilizing a translucent partially reflective film. Moreover, the latter system incurs manufacturing problems in ensuring completely flat spectral characteristics and good color reproduction in the viewfinder.


The AL-1's Quick Focus system was the early application of one of the most advanced optical and electronic technology during the early '80s. You can see an early formation of the focus detection method each manufacturer tried to invent in a form of proprietary AF system on their own.
(Note: Except for Canon, virtually all the current AF system used by the Japanese and European 35mm SLR camera manufacturers are from Honeywell's patented CCD's phase detection system and eventually all of them have to pay an undisclosed high sum as royalties after a lengthy legal battle ended nearly a decade ago in the US of which Minolta Corporation Ltd lost the case with their Maxxum series of AF SLRs).

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The AL-1's focus detection system measures light entering through the lens. The light is guided to a triple beam splitter located at the bottom of the camera via the patterned main mirror and a sub-mirror. As it travels through to the CCD line sensors underneath, the light beam is separated into three parts by the triple beam splitter.

The center line sensor is placed so that the focus of the image formed on its surface corresponds to the one that will appear on the film. The two outer line sensors compare the image contrast with each other (the focus is sharpest when the image conditions before and behind the center line sensor are the same.). The center line sensor ensures that a false signal is not generated in case the image is extremely out ot focus. The microcomputer performs all image contrast calculations and transmits the data to the LED focusing indicators in the viewfinder.

Triple Beam Splitter The principle used in triple beam splitter is very much similar to the ways used in modern AF SLRs. Together with the CCD line sensors, it forms the heart of the Quick Focus system. Composed of three reflecting surfaces and four microprisms, the triple beam splitter divides the incoming light reflected by the sub-mirror into three equal parts, which then proceed to the CCD line sensors below In so doing, it fulfills several crucial requirements. It correctly divides all types of light, ensures that the image characteristics are identical for all three CCD sensors irrespective of the image pattern, and guarantees that the degree of blur in the front and rear directions is the same when the camera is in focus and also that ghost images won't affect the performance.

TripleBeamillus2.jpg

In order to ensure that the sensors" fields of view are identical an extremely high degree of precision is required of the microprism. Canon achieved this by developing an entirely new manufacturing process. way or another, the Beam Splitter was used for 3 Metering modes for the
Canon New F-1 system. Good applications ..

ccdsensor.jpg
Three CCD Line Sensors
The extreme accuracy of the QF system is largely due to the use of three CCD (Charge Coupled Device) line sensors to detect the image.


Each of these CCD incorporates 112 cells which partition the subject into minute sections and convert them into electrical signals. These signals are serially transferred to the SFP (Sharpness Function Processor) for analog processing and then to the CPU (Central Processing Unit) via various intermediate processing stages. The CPU controls the Quick Focus system and generates LED information in the viewfinder. The CCDs, with their 112 micro-eyes, are able to measure even tiny subjects. They also exhibit a wider dynamic range with high sensitivity and low dark current, permitting a ranging illumination level of EV3.5 - EV18 (ASA 100 ISO 100/21°). And due to their all-solid-state design, they are quite reliable, generating neither electrical nor mechanical noises. The CPU performs a host of complex calculations and cross comparison of data in microseconds. It aids you in producing perfectly exposed and focused pictures.

Two Exposure Modes for Exposure Control The AL-1 offers two alternative paths in exposure control: Aperture-priority AE and Manual mode. With the former, you choose the aperture and the camera automatically selects the shutter speed. The shutter speed is electronically and steplessly controlled from a fair 1/1000 sec down to 2 full seconds.

Aperture-priority AE

Auto Dial.jpg

This exposure mode gives you greater control of depth of field (the area in focus before and behind the subject) and indirect control of shutter speed. Above all, aperture-priority AE is simple and as I said earlier, strangely Canon is reknown for their shutter priority AE and it was omitted from the feature list.
Lens Aperture.jpg


Backlight Control Switch
When you are in the AUTO mode, sometimes you might be expericing some unfavourable lighting situation such as back-lit subjects which may sometimes come out too dark unless you compensate in the eventual image.

BackliteBTN.jpg
This handy switch solves the problem. Press the button while taking the picture and exposure will be automatically increased 1.5 X. The AL-1 has no exposure compensation dial for finer fine tuning of exposure other than this button. Well, unless you know how to make use


Manual Exposure Control However, should you decide you want to take over from the AL-1's automation in exposure control and do everything yourself, the AL-1's manual facility gives you full room to display your creative talent. but the disappointing side is the option to control the shutter speed in full scale, as the AL-1's weakest link is circled around the manual shutter speed dial - it has only 1/1000 to a low of 1/15 sec speed scale. That seems a little fragile for it to 'qualify' as a versatile imaging tool.

Manualdial.jpg
The selector dial has a safety lock to guard against accidentally disengaging the A setting. Depress the lock release button on top and turn the dial to the desired shutter speed. Then choose an aperture.
Shutter Lock.jpg


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Various Canon
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