Subject:	A few more words on settings
Author:	javier
Date:	9/1/2002 10:06:11 AM
Message:

Are you using a Canon eos?
I have spent some time searching for more information on the light metering modes of the eos cameras.
My apologies if it is not relevant for you, perhaps it is to others... :-)

It seems to work like this:

When the camera detects an external strobe it now decides that the spot where you are focusing is going to be the location of your subject. The camera now makes a separation between the so-called "subject" (focusing area) and the "background" (the rest of the frame).
What happens now is that the camera will try to make a correct exposure for
1) The background: using all the light-metering segments that are far away from your focusing point (therefore representing the background). According to this light-metering it will choose any speed in the range of 30seconds-1/125-or whatever your camera can sync (I assume you're working on "A" mode and you choose by yourself the aperture).
2) The subject: the camera will use the TTL-segment (out of four in most eos cameras) that is nearest to the focusing point, and will control strobe exposure according to this segment.

As far as I understand, these settings are set AUTOMATICALLY by the camera, regardless of whatever metering mode you have selected in your camera! i.e. "spot" or "center-value" are overriden when your camera detects a strobe..
For these reasons Canon do not recommend to do "Aperture locking" (focusing one spot and then moving the camera with the button half-pressed to another spot) when you are shooting with an external strobe, since you will fool the camera's exposure algorythm and get bad results!

What happens at night? Camera will insist in correct-exposing the dark-background, asking for speeds of several seconds => not applicable for us who shoot without tripods...
What can you do? If you have custom functions in your camera, there is one that forces the camera to use always its highest sync speed (1/125 in most eos). You choose the aperture and the camera uses 1/125. Just don't forget to turn the darn function OFF for daytime :-)

What else? Turn to "P" mode and it will choose automatically a suitable speed for hand-photography (1/60-1/125) and whatever aperture it thinks. You cannot change this automatic selection (without the strobe you can switch various exposure settings, with the strobe there is only one...)

Last option: Turn the camera to "M" and choose a speed in the range of 1/60-1/125 and whatever aperture you were intending to use if you were in "A" mode. The camera will yell to you that you are underexposing (because she thinks you want to expose the dark-background) but since you're in manual mode you can do whatever you want, so just shoot and TTL exposure (or manual, if you choose the aperture according to your distance which is more difficult to estimate at night) will be correct anyway.
Of course, you will be able to see only the subject and the background will be completely dark, but that's how things work at night, ain't it?

Hope you find it usefull..

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