--- Vesa Perala <[EMAIL PROTECTED]> wrote:
> My concern is how do I avoid OVERexposed backgrounds
> in such case?
> I can live with dark backgrounds because they are
> often unavoidable
> with flashes.
>
> Sometimes the background exposure is changing so
> much that using
> one setting in M-mode would cause overexposure in
> some photos.
> Watching and changing the exposure could mean
> loosing some moments
> (thus photos).
>
> Av and P-modes could and would mean too long shutter
> speeds.
NO. In P mode, the camera will not set a shutter
speed lower than 1/60th second.
> Tv-mode would mean that camera is using the largest
> aperture
> when light level gets too low.
TV mode (like AV) is also designed for fill flash.
The camera will try to set an aperture to properly
expose the background and use flash for forgound fill.
>
> Solution 1:
>
> If I could limit the slowest shutter speed in Av
> mode to what I want
> (e.g. 1/focal length) when flash is on and ready I
> could set
> the aperture to what I like and flash and Av mode
> together would
> take care of the exposure, both for foreground (Av
> and flash) and
> for background (mostly Av mode).
We're back to square one. You get EXACTLY the same
effect by selecting manual, setting the shutter speed
to 1/focal length, and adjusting the aperture to what
you want. This is exactly how AV mode with the
ability to limit the shutter speed would work. But
the flash system CANNOT, in this situation, expose for
both the background and forground. Background
exposure is set by the combination of shutter speed an
aperture chosen, and foreground exposure is controlled
by the flash.
The ONLY way you could get both exposed properly is if
the background is essentially right behind your
subject.
> Using the SafetyShift function (e.g. EOS-3) would
> give the "best"
> possible background exposure because it would allow
> the camera to
> select larger aperture than what I selected when the
> set shutter
> speed limit has been reached.
>
Unfortunately, I don't think this shift works with
flash at all, in any mode. Would be nice if it did.
> Solution 2:
>
> Also P-mode with limited slowest shutter speed or
> Tv-mode could
> be practical when you don't care about the selected
> aperture but
> just want the background exposure to be as good as
> possible.
This is how P mode works. It chooses a shutter speed
at 1/60 or higher, and a aperture, to attempt to match
subject and background exposure. If the distance
between the forground and background is close, or the
background is pretty brighly lit, it does a good job.
But if the background is very dark, or far behind the
subject, there's nothing the camera can do. The laws
of physics say the the intensity of light diminishes
as the square of distance. So if the subject is at 5
feet, and the background is at 15, the light (from
your flash) hitting the background is only 1/8 as
intense as the light hitting your subject.
There's no way ANY camera and/or flash can properly
expose both.
=====
Bob Meyer
Life is uncertain. Eat dessert first.
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