Vesa Perala wrote:
>
> > > But the exposure time would never exceed the limit, e.g. 1/focal
> >length.
>
> >This is exactly what P-mode does. So every EOS-body has it, and we al know
> >the results it's given us.
> >
> >Drikus
>
> It does? So you mean in P-mode the shutter speed never goes slower
> than 1/focal length (with flash)?
> Oh boy... forgot that possibility. 8-|
> I remembered P-mode works the same way with or without a flash.
>
With A-TTL type bodies at least, P mode will NOT prevent shutter speeds
longer than 1/focal length. Instead it will choose a shutter speed
between 1/60 second and the flash sync speed. There's also no way to
use program shift. Don't know about the E-TTL generation, though ;-)
All this is for use with flash of course.
Then again, is there really a need for 1/focal length rule when using flash?
When flash is the main light source, the flash will freeze the subject.
And when using fill flash in a rather bright environment, AV or P will
give fast shutter speeds. I think there is a fundamental problem with
flash, you cannot have all of the following at the same time
- Control over aperture
- Control over shutter speed (This includes things like 1/focal length rule)
- Perfectly exposed background
If you set an aperture which requires 1/4 second for the background
exposure, you'll never get a well exposed background with a 100mm lens
at 1/125 second. On camera flash has its limitations that we all have
to live with. Either you get a real fill flash mode, which balances
foreground (flash) and background (ambient) exposure nicely but might
lead to slow shutter speeds or large apertures. Or you get a mode that
gives you control over everything, but then the background may be
underexposed (or overexposed in extreme situations), depending on the
ambient lighting and your chosen settings.
Thomas Bantel
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