Several weeks ago I came across the manual for the F280, and realized why it
confuses everyone so badly. The manual is badly written, thoroughly confusing,
and downright misleading. So are the markings on the flash, which imply that
Super FP provides auto exposure, which it absolutely DOES NOT.
I wanted to write a long explanation, but I don't have the time. For now,
here's a quick rundown.
The output of an electronic flash lasts from about 1/300 to about 1/3000 of a
second. A small shoe-mount unit usually pops its capacitor load in less than
1/1000 of a second.
This is shorter than the fastest shutter speed of a leaf shutter. So the
shutter speed in leaf-shutter cameras has no effect on the exposure produced by
an electronic flash -- only the aperture does. This allows the aperture and
shutter speed to be set independently -- the aperture for the amount of fill-in
desired, the shutter speed for correct ambient exposure.
When an electronic flash is used with focal-plane shutter cameras, the shutter
has to be completely open when the flash fires, or part of the image will be
cut off. No focal-plane shutter can open fully in less than 1/250 of a second.
Most fall in the range of 1/100 to 1/125. The OM cameras have a relatively slow
flash sync speed of 1/60.
This causes problems when using fill flash. The shutter speed can't be any
faster than 1/60, which in turn requires a very small aperture, which in turn
requires a powerful auto-exposure flash (or a high-powered manual flash with
variable output).
So... wouldn't it be nice if we could use electronic flash at speeds where the
shutter _isn't_ fully open? The only way to do this is to fire the flash
hundreds of times, so that it looks as if its output is "continuous."
When you switch the F280 from regular to Super FP, you convert it from an
automatic flash to a _manual_ flash whose output lasts for about 1/50 of a
second. (Despite what most people think, and what the switch on the F280
implies, Super FP operation -- as far as the flash is concerned -- is manual.)
You can use any shutter speed from 1/60 to 1/2000, and the flash will synch.
But because the flash is now a "continuous" light source, you've lost the
ability to set the aperture and shutter speed independently -- all
EV-equivalent shutter-speed/aperture combinations produce exactly the same
exposure from the flash.
To put it another way -- when using the F280 for fill-in, you're stuck with
whatever the F280 emits. The only way to change the amount of fill-in is to
change how far the flash is from the subject, or some light-absorbing material
over the flash. This is why the F280 works beautifully in some situations,
poorly in others.
The chart in the manual can be useful in deciding how far you should stand from
the subject for "correct" fill-in.
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|