Shannon Hong wrote:
>
> Dear Nicolas,
>
> I don't have the flash manual for the F601 - could U explain to me how the
> analog display for possible flash over or underexposure works?
>
> Even with the onboard flash activated - my F601 still shows possible
> underexposure of the backgrd.
>
> How does the flash know what the GN of my SB26 or Metz 45CT4 flashes are to
> predict possible flash over or under exposure? Do the flashes tell it what
> GN it is(which I find improbable)?
>
> I can never get the camera to show correct exposure unless I set it to very
> slow shutter speeds or wide apertures in full Manual or Shutter priority.
The analogue display shows the over/underexposure of the background,
i.e. what will not be lit by the flash.
Auto exposure works as follows:
1 - Speed and/or aperture values are chosen to insure a properly exposed
background (based on ambient light)
2 - If you pop up the flash, the latter is used to fill in a foreground
subject, either by normally measuring the flash output (straight TTL) or
by balancing flash and ambient light (balanced fill flash), which
normally means that the flash exposure will be corrected towards
under-exposure (balanced fill flash does NOT change the aperture/speed
values, hence the background exposure, only the flash output).
Now, this is an ideal description, because when using a flash, the
ambient light is usually LOW, and a normal speed (1/60s to sync speed)
is not long enough to enable proper background exposure. That's why the
analogue display shows underexposure: the foreground should still be lit
by the flash, but the background will remain dark. To work around this,
you may enable slow speeds, by setting the slow sync mode.
On the other hand, if you're trying to fill in a foreground backlit by a
very strong light, it may be that the fastest sync speed (1/125s for the
F601) is not rapid enough to avoid overexposure of the background. In
this case, the analogue display will show over-exposure.
Remember, the analogue display is about the exposure of what will NOT be
lit by the flash.
Hope this helps,
Nicolas
