Modern Classic SLRs Series :
Canon T-90 - Detailing its Metering Capabilities


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Center Weighted averaging metering

Spot metering

Partial metering

A-TTL/TTL
Flash metering

Given the T90's sophisticated three-way metering system, every type of lighting condition can be accurately assessed for optimum results. The T90 offered the world's first metering system with three easily switchable metering distribution modes rather than changing screens like the case of its 'elder' brother, the Canon New F-1. The one used on the T90 was a more responsive way as the selection was instant simply by using the Electronic Input Dial and pushing the Metering Mode Selector.

I would like to take this opportunity to explain a little more on the things that are related to these metering patterns of the T90 (so I don't have to explain further in other cameras, ha!). Among the few options available, the most common mode is the center-weighted average metering, that is used by almost every conventional 35mm SLR cameras.

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Average metering means that the light values over the whole picture area -with some emphasis on the center - are averaged for an overall reading. If the light is evenly distributed over the entire scene, such as a landscape, or if there is an overall balance of light and dark areas, then this metering mode is easiest to use and yields the best results.




While the center-weighted average metering may solve most 'general' situations, there are times where it may not yield the best and accurate result, requiring you to use your own experience to perform the exposure compensation or exposure adjustment manually. Back lighting is a typical example. The apparent advantage of the T90's Partial metering mode (the first Canon model to employ this metering was the Canon FTb of 1971, which also allow TTL Stopped-down metering, thus, it is not new with this T series model), which measures mainly the center area of the picture, about 13% of the total can be quite useful as an exposure reference. It's particularly useful when the main subject is surrounded by an especially light or dark background.

This mode is also appropriate for portraits of a single person. By measuring the subject alone, the exposure will be correct no matter what the background is. The AE lock feature can be used to "lock-in" the memorized exposure values if you want to recompose the scene with the subject not in the center of the frame and readjust your composition later.



Adverse lighting condition, may require even more precise control. The spot metering mode measures only about
2.7 % of the picture area, providing the photographer with extremely precise exposure control.

It is often chosen for very difficult shooting situations, as when a small subject is surrounded by a much larger, and much brighter or much darker background. By using the spot metering mode, only the subject's light value is considered. The spot metering mode also has a 30 sec memory and work in combination with AE lock.




The AE Lock is useful when the main subject of your photograph is not in the center of the composition. When shooting with the partial or spot metering mode, pressing down the shutter button halfway engages the AE Lock mechanism. Simply aim directly at the subject, engage the AE lock mechanism, then recompose your photograph, moving the subject out of the center if you wish.

The T90 automatically memorizes the metering data, ensuring correct exposure. No matter where your main subject is located in the scene, you may use the AE Lock mechanism to get just the eventual results you had envisioned earlier in your mind. I use the AE lock feature very often whenever I am in the auto exposure mode, including center-weighted average metering. It comes in very handy indeed.




Both the Olympus OM3 & OM4's innovative Multi-spot metering system created a stir when the cameras were launched. The metering system has a wide following among some purists because it was based on the principle of the Zone System. Generally, the T90 has no innovation as far as the metering section is concerned as all the available options are either upgrades from Canon's own primary metering technology or a compilation of what the market has been offering. Anyway, for those who has all the time in the world to "construct personalized" pictures before tripping the shutter, the T90 does have this option available. It is a fact that the Multi-spot metering makes complex lighting decisions more precise in most cases. The T90 offered Multi-spot metering for those pictures that demanded a balance between highlight and shadow areas. The photographer can take spot metering readings of
up to eight essential points. These are then averaged by the camera to determine the final setting. It came with a rather easy display to read viewfinder info that shows each reading.

While the Multi-spot metering is based on the principle of the Zone System, it has to remember that this mode will not work all the time especially when the T90 is loaded with color reversal films having very limited exposure latitudes. The camera will not not be able to distinguish a color print film from a reversal type or a black and white emulsion. It can only recognized the film's ISO speed and set its metering recommendations based on it, taking into consideration the lighting conditions involved. For best results when shooting with color reversal films, the differences in exposure values between the highlight and shadow areas should not be higher than 1-1/2-stops. This does not only applies to the T90 but any model having the Multi-spot metering feature -- Philip Chong

Is that all ? No. Apart from Multi-spot metering, Canon had also "borrowed" another of Olympus' auto exposure control function: The Highlight and Shadow Control feature.

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The multi spots meter will display its averaging or preferred setting after calculations.





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Another impressive feature offered by the Olympus OM3 & OM4 was its Highlight and Shadow Control function as you can recalled.:
"The splendid reality of brighter, purer whites and deeper, richer blacks".
Dating back to the early debut of auto cameras, most of them only have a variable of two stops up and two stops down in shadow control via the exposure compensation feature. At the later stages, the play was on precise controls like from a full stop changed to a 1/2-stop or even a 1/3-stop increment of fine tuning the exposure compensation. This method was considered as adequate for most situations, especially with the aid of an exposure lock (AE Lock).

But this type of exposure compensation can be restricted in certain situations, as the two stops of -/+ variations may not yield satisfactory results. All the cameras' metering tend to reproduce predominantly white or black scenes with a dull gray cast because of the extreme differences of their reflectivity. This is further complicated by the film's exposure latitude as well.

Just like Olympus cameras, the T90's variable Highlight control uses Spot metering to let the camera "see" whites in all their pure whiteness. And unlike other H/S controls, the T90 system allows the photographer to compensate for different levels of brightness by adjusting its Highlight compensation by up to 4EV in half-step increments for enhanced effect to reflect the more precise interpretations.

The Shadow control works like the Highlight control to keep blacks dark - the way they appear naturally. And, like the Highlight control, compensation can be adjusted according to how dark the subject is. Again, variable compensation ensures that the photographer can achieve the exact tones desired. Without Shadow compensation, black tones appear weak and washed out.

But how do you know the required amount of compensation needed to ensure whites turns out white and blacks to be black? Simple. Compensate two stops in either direction for both whites and blacks from what the camera has suggested. In reality, the Highlight and Shadow control is another way to allow exposure compensation when using the T90 in auto exposure mode. Or one can consider it another variation of using "Manual" during AE mode - Highlight means open up and Shadow is minus the exposure value over what the camera has suggested.

But Canon perfect this control based on its own way. The T90 allows you to control the exact degree of compensation you want. There can be any number of "good" photographs using the Highlight/Shadow control which is conveniently located just at the back - within reach of your thumb. The H/S technique is not limited to blacks and whites only. It can also be used to make vivid colors even more exciting or to deepen somber hues.

If one tends to be fuzzy enough, you may prefer to consider using Nikon's Multi Segment Evaluative Metering (First seen on the Nikon FA in 1983). But given the awesome and broad choice of the various metering options the T90 has, the camera itself is more than adequate for all you will ever need. I don't even bother to use any of the other options of my camera, opting instead for the standard center-weighted average metering as my main reference. I doubt very much anyone of you will be switching from one option to the other from time to time with all the options provided. It is very likely to be more of a case in figuring how to set the control than anything.. ha!

Jokes aside, to complete the Metering and exposure control, the T90 does has the conventional way of doing exposure adjustment - The exposure compensation, only in a more advanced way.

When you want high-key (intentionally overexposed) shots or low key (intentionally underexposed) shots, you can adjust the degree of exposure by using the Exposure Compensation Index.

Press the Exposure Compensation Button. The Exposure Compensation Index will then appear on the Display Panel instead of the film transport bars. While pressing the Exposure Compensation Button, turn the Electronic Input Dial to move the dot from under the 1 (indicating no exposure compensation) to the desired point on the Exposure Compensation Index.

By using the Exposure Compensation function, you can adjust the degree of control wanted in order to get the optimum exposure. Moreover, since the mechanism is fully automatic, you can shoot continuously without worrying about having to do spot metering with AE Lock for the correct exposures.

The T90 accepts a wide range of film speeds, from ISO 6 to ISO 6400. Since the Exposure Control can function at both ends of this spectrum, an incredible operating ISO range of 1.5 to 25,600 is possible.

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