Modern Classic SLRs Series :
Canon T-90 - Exposure Control
Shutter Priority AE /Stopped Down Metering


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Many have mistaken the Canon AE-1 of 1976 as the first Canon to employ Shutter-priority automation. Well, prior to that, the Canon EF in 1973 already has a shutter speed-priority TTL automatic exposure incorporated within. Its hybrid copal square shutter control speeds from 1/2 sec. to 1/1000 sec and bulb mechanically while slower speeds from 1 sec. to 30 sec. were electronically-controlled. The AE-1 was a true Shutter-priority AE camera. Anyway, no one doubts that Canon has the leading edge in the development of Shutter-priority automation - for a brief spell, Minolta did surprise many with its debut of the XD-7, which was the first ever multimode SLR, and Canon relied handsomely with its highly successful Canon A-1to counter any threat from that model during the late '70s. Well, just for the information, the first Nikon permitting Shutter-priority AE was the Nikon FA in 1983 after they have upgraded the Nikkor lenses to the AI-S series.

Although most of the manufacturers preferred Aperture-priority AE than Shutter-priority AE, which doesn't involve the physical change of the communication of data input between the lens and camera body, Canon's persistent was seen as quite 'odd' - but t
he Shutter-priority AE mode found its core supporter with sports photographers and other professionals. With the T90 operating in the Shutter-priority AE mode, you can capture all the action by selecting the appropriate shutter speed. You dial in your choice via the same convenient Electronic Input Dial, selecting from 35 different speeds–ranging from 1/4000 sec. 30 sec. in half-step increments for the ultimate in precision. Once the shutter speed is set, the T90 automatically selects the correct aperture.

Well, the "which mode is better" debate has been going on for the last 2 decades. Both have their strengths and weaknesses as the preferred automation in camera operation. Being two of the main features of any modern 35mm SLR camera, the factors are interlocking. Basically, both the shutter speed and aperture values alter effects. We have briefly described on the aperture earlier of the eventual effects it might yields with varying values. With a shutter speed control, say, in order to capture a sense of motion - lower speeds are best suited to achieve such effect. On the other hand, the use of fast shutter speeds for photographing a fast action event like racing cars can have an opposite effect, making them appear to be frozen. Well, it is possible to achieve an almost unlimited range of photographic effects just by being aware of what happens when you use different aperture settings and shutter speeds.


Half step shutter speeds ? No problem.
Note the "Tv" setting appeared at shutter priority automation.


* Refer to the main map of T90 for cross reference.

How to set the mode ? While pressing the Shooting Mode Selector, turn the Electronic Input Dial until the Shutter-priority AE mode symbol (Tv) (Time value) appears on the Display Panel. Release the Shooting Mode Selector and continue to turn the Electronic Input Dial until the shutter speed you want appears. The correct aperture is shown inside the viewfinder, so you can check the shutter/aperture setting without looking up from the lens you are photographing.

The input dial is an integral part of the whole system for command.As most of the required tasks or changes can be handled by the Electronic Input Dial. It lets you to easily and quickly choose from among a total of 35 different shutter speeds.


No matter how quickly the pace of the activity you are shooting changes, you can dial in a new shutter speed to match it. This unique feature of the T90 is sure to improve your high-speed shooting technique. And it is particularly useful when you need to work with the fastest possible shutter speed in dim lighting.


The safety button can be activate to monitor out of exposure range and put you back in command. There is a safety control feature for the unexpected. The T90's Safety Shift can be switched on to automatically override the set shutter speed in order to avoid over or underexposure.


If the selected shutter speed is too slow or too fast for existing light conditions, the T90 automatically switches the shutter speed to the correct setting. To set the Safety Shift mechanism, you simply press both the Film Speed Button and the Exposure Compensation Button at the same time for approximately 1 sec. The "SS" mark will appear on the Display Panel, indicating that Safety Shift will be activated if necessary.


For special creative effects or intentional over- or underexposures, pressing the same two buttons disengages the Safety Shift function.

Blur for portraying movement or action freezing ? The possibilities can be endless. The T90 can free you to experiment with your creative sense or preference.


Note: PLEASE USE the MAIN MAP for the viewfinder and LCD display for cross reference in this site. Another page is also equally helpful for its layout of controls and buttons.



Have we forgot about the basic manual setting ? Well, if all of these advanced automation are not your cup of tea (Why buy it then?), the T90 has the Stopped Down (Fixed Index) Metering for you to toy around. It allows complete manual operation.



Even when you are in this mode, you can still check for correct exposure by simply selecting the shutter speed using the T90's Tv mode and then adjust the f-stops from the aperture ring, after disengaging it from the 'A' mark. The viewfinder display indicates correct exposure, over and under exposures and "help" will appear to instruct you to close or open the aperture.

manual mode.jpg
The stopped-down AE mode is used when shooting with non-FD lenses like the Canon FL lenses or with FD lenses mounted to close-up accessories such as FL-type of extension tubes or bellows, both of which have no signal pins.


By selecting the T90's aperture priority AE, standard Program AE, or variable-shift program AE, you can directly choose the aperture setting using the aperture ring on the lens then push the stop down lever and the T90 automatically determines the correct shutter speed. Thus, by this method, you can still enjoy AE performance even with a 7.5mm fisheye lens, Reflex lens or TS lens. The Canon TS (Tilt and Shift) lens has no Automatic Aperture Lever and you can use this mode to perform metering this way).

* Refer to the LCD main map of T90 for cross reference.

Macro photography presents particular problems in controlling depth of field because of the very short focusing distances. When using a bellows or extension tube between the camera and lens, the stopped down AE mode is essential because there are no FD-type of signal pins to interlock to the "A" mark.


* Note: If during the Stopped Down mode, you accidentally set the lens to "A" mark, the error message will appear. Click here for an illustration. With the T90 in the stopped down AE mode, you can control the effects you want since you can visually observe depth of field while selecting the aperture values. Stopped down AE makes even "Pinhole" photography easy since the T90 is so sophisticated, it can take even a "pinhole" photograph using AE operation.



You can use the Stop Down Lever to visually confirm the depth of field when shooting in the stopped down AE mode, the most commonly used method when using lenses without FD signal pins.
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Maintenance Team: Credit: Pawel Nabe for his image on the Data Memory Back. EEwyn Foo, my nephew, who has spent quite a number of nights converting the original manual in HTML format. Mr. Richard Yeow, General Manager -Optical Division of Canon Marketing for granting special permission to reproduce this manual into HTML format in his site as a form of obligation to all the T90 users worldwide. Maintainders of the T90 Message Board: Kaipin, Terry Carraway & Dr Strangelove; Tom Scott, for his images of the SPD cell, Chris Tutti for his initial effort to scan and prepared the T90 manual in PDF format. My staffs Miss Wati and Mirza for helping the basic setup work. * Canon, T90, FD Lenses, Canon Marketing are registered trade names or trademarks of Canon Inc. Japan.