Metering Modes Revealed - Part I

Started Jan 30, 2004 | Discussions thread
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pbleic
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Metering Modes Revealed - Part I
Jan 30, 2004

For ambient metering (flash metering gets more complicated):

There are three basic modes available on your KISS Digital. (Digital Rebel, 300D) with some variation:

1. Partial Metering:

In use in ALL creative modes, only when AE lock ( ) is pressed, and for 16 secs afterwards. Looks at the center 15% of the field (regardless of focus point). Treats whatever object is in the center as 18% reflectance. That means, if you press * while pointing at a black object, you will get overexposure; while pointing at white - underexposure. You can use it on anything middle reflectance - a grey card, northern blue sky, weathered wood, foliage.

Perfect for when you have a subject that you want to be properly exposed.
2. Centerweighted Average:

Metered as above diagram indicates, covering most of the field. Available ONLY in Manual exposure mode. It is the "tried and true" metering that has been around for 40+ years. It also uses 18% reflectance as a target, but "averages", weighting more towards the center, the field and exposes as if that was 18%. For those comfortable with an old SLR, you will be most comfortable with this metering. It is easy to use once and gives you tons of creative control. I find myself using it most often because I set the metering ONCE and keep it there for a particular scene - only changing with change of position or lighting. Any "non-manual" metering changes without my knowledge or control.

3. Evaluative Metering - the most complex mode. Basically, the camera measures exposure based on 35 non-equal segments (see a diagram of the old 21 segment map):

It uses ANY active focal points for very significant weighting. This way, it will make sure these focal points are properly metered and will attempt to IGNORE bright highlights and dark shadows - exposing your entire scene properly, but especially your subject. Once it measures subject distance, focal length and luminance, it compares them to an extensive, IN CAMERA database using its iSAPS technology in the DiGIC processor. This database has similar curves for many common photographic scenes and uses them to choose the correct AE mode, Auto White balance, colour processing, tone reproduction and focusing for the scene. Here is the type of information that is compared:

Evaluative metering takes some getting used to, but it can be excellent. If you are trying to use it with center focus ONLY, you will undoubtedly have inconsistent exposures. However, learning to effectively use the 7 AF points is an art.

Here is an EXCELLENT article on how to use evaluative metering to its best advantage: http://www.camera.canon.com.my/archive/photography/art/art14/index.htm
Doug Kerr has developed a table that indicates when each is used:
http://doug.kerr.home.att.net/pumpkin/300D_metering_DAK.pdf

Note that, in one special circumstance (Manual Focus in creative modes) the metering is evaluative, center focus point only. Although Chuck Westfall says this, I am still a little unsure of this, as it is possible to activate multiple focus points with manual focus.

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Paul

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