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Canon G3 spotmetering (spot metering) / Exposure / Operational cheat sheet


A reader reviews the spotmetering book at amazon.com

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If you do not want to read the book titled "the confused photographer's guide to on-camera spotmetering (spot metering / partial metering)
ISBN: 0966081706" simply read the following:

The on-camera spotmeter (spot meter / partial meter) is the most powerful exposure tool in the world. Read the following page and decide for yourself if you understand the concept. If you do understand everything on the following page, and you can apply the technique described and produce correctly exposed images, then that is all you need! If, however, you even have the slightest doubt about this technique, or if you are still the least bit confused, this book is for you.
Remember: either you know how to use your on-camera spotmeter effectively or you don’t. There is no in-between! I believe this is the simplest, easiest, best illustrated, and most practical book about on-camera spotmetering in the world.


Cheat sheet: The entire book condensed onto one page (well almost!)

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Set the ISO of your Canon G3 to 100 and choose an outdoor subject. Activate theSpot metering/Partial Metering option on your G3 and set your camera’s mode to manual and to the shutter speed to 1/500 or 1/1000 sec. 

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Observe your subject and break it down into its simple subject (single tone) components. Choose a Reference Tone.  A Reference Tone is a simple tone (one tone) usually chosen from the most important part of the subject. Once you have selected the Reference Tone, point your spotmeter circle at this tone so that the spot frame falls WITHIN this simple tone and find its normal exposure. If your subject does not have a distinct single tone pick out a tone that is medium gray or brighter.

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Let’s assume the "normal exposure" indicated by your camera for this Reference Tone is 250@f-5.6 (i.e., 1/250 sec. at an aperture setting of 5.6).
As you may know, the spotmeter’s "normal exposure" from any simple (single toned) surface will always provide the photographer with an 18% gray image tone (or a Grayscale density of 128 (out of 256) in photoshop on your home computer when you convert the image to black and white/grayscale).
The image tone that your camera's normal exposure provides is independent of the original tone of your subject!

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In spotmetering, converting the "normal exposure" to the "correct exposure" is what a photographer must do. In other words, the "normal exposure" readings of the spotmeter must be interpreted by the photographer to determine the subject’s"correct exposure." The principle behind this simplified technique is that if one tone of a complex subject is exposed correctly, the rest of the tones follow and will also be correctly exposed . Now decide which one of the following tones would most closely matches your Reference Tone: Black, Dark Gray, Medium Gray, Light Gray or White. With this simplified technique you must choose one of these five tones. Once you have decided which one of these five tones best matches your Reference Tone, then adjust your camera settings accordingly:

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If you chose Black, you need to decrease the "normal exposure" setting by two stops. Decreasing the exposure time  by two stops converts the 18% gray image tone to Black. The correct exposure is now 1/1000@f-5.6 or equivalent.

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If you chose Dark Gray, you need to decrease the "normal exposure" setting by one stop.  Decreasing the exposure time by one stop converts the 18% gray image tone to Dark gray. The correct exposure for this is 1/500@f-5.6 or equivalent.

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If you chose Medium Gray, leave the aperture and shutter speed as they are since the meter is already creating an 18% gray (Medium Gray) image tone, i.e., the tone of the image matches the approximate tone of the Reference Tone. Also remember that when metering from a medium gray surface, the "normal exposure" and "correct exposure" settings are approximately the same. In this case the correct exposure is 1/250@f-5.6 or equivalent.

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If you chose Light Gray, you need to increase the "normal exposure" setting by one stop. Increasing the exposure time by one stop converts the 18% gray image tone to Light Gray. This results in a correct exposure of 1/125@f-5.6 or equivalent.

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If you chose White, you need to increase the "normal exposure" setting by two stops. Increasing the exposure time by two stops converts the 18% gray image tone to White. The correct exposure would be 1/60@f-5.6 or equivalent.

 

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