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Old Feb 9, 2005, 8:19 PM   #11
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:? jb Sorry, didn't quite ask the question right. What I was thinking is if you set the TV, shouldn't the cam set the AV automatically to compensate and vice versa, instead of changing shutter speed.
What has happened to me is I expect a faster shutter speed and then move the camera or something as the shutter is much slower. End results is a bad shot.
Could you advise why we would want to leave this function on?
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Old Feb 9, 2005, 9:27 PM   #12
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Sometimes the lens can't open up enough to provide good exposure for the selected shutter speed. When this happens and C.Fn-16 is enabled, the camera drops the shutter speed to maintain a correct exposure.

Once the exposure has degraded enough to enact C.Fn-16, you should adjust your settings. Maybe bump the ISO a bit, or switch to Av mode and open the lens to its full aperture so that you get the fastest shutter speed possible.


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Old Feb 10, 2005, 8:45 PM   #13
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:? What do you feel are the disadvantabes of disabeling the function?
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Old Feb 11, 2005, 10:36 AM   #14
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Golfer wrote:
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:? What do you feel are the disadvantabes of disabeling the function?
In general, if the exposure degrades using either Tv or Av, and you hit a maximum setting (aperture or shutter speed), you will not get the picture you want.

In specifics, let's say you have a 500mm F4.0 lens. You set the shutter speed to 1/500 in Tv mode and the metered aperture is F4.0. All is good.

If C.Fn-16 is enabled, and the sun goes behind a cloud, the camera will try to open the lens for the correct exposure. But it can't because it is a F4.0 lens, so it drops the shutter speed to preserve the proper exposure. The end result is a picture that might be blurry, but will have the proper exposure.

If C.Fn-16 is disabled, and the sun goes behind a cloud, the camera will try to open the lens for the correct exposure. But it can't because it is a F4.0 lens, and it can't drop the shutter speed because C.Fn-16 is disabled. The end result is a picture that will have the shutter speed you selected, but will be underexposed (dark).

You can see that neither of these solutions really give you what you want. You need to be aware of the exposure, or lighting, all the time while you're taking pictures. If you're on the limits of your lens and the sun goes behind a cloud, you need to notice it and make an exposure change... Bump the ISO setting a bit... put on a faster lens... wait for the sun to come back out... something.

Hope this helps...


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Old Feb 11, 2005, 8:43 PM   #15
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jb Thanks, that clears things up for me.
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