Matt BenDaniel wrote:
I found an interesting article here:
http://www.rit.edu/~andpph/text-streak.html
Thanks for powting the link. I've seen it before, but lost track of it.
It provides much more clear info than any other source I've seen.
Apparently in Super FP mode, the F280 pulses about 10000 Hertz. This implies
that the F280 would flash 5 times during a 0.5 millisecond exposure. That does
not sound equivalent to continuous lighting. For example, with moving
hummingbird wings, this could yield some interesting artifacts.
I don't think they were thinking about stopping very fast action.
It's also too bad that the engineers didn't make the F280 capable of delivering
a very bright duration of a few milliseconds that supports a shutter speed of
1/2000s with a reasonably strong guide number.
No, shorter shutter speed doesn't mean shorter flash duration. With a
focal plane shutter, at speeds above the synch speed, a faster speed
simply means a narrower slit traveling across the film at the same
speed. Thus, the flash duration has to be the same no matter what the
shutter speed as long as the curtain travel speed doesn't change. The
result is that the guide number decreases with increases in shutter
speed, since any given point on the film is exposed to the same light
for less time. The effective flash power at 1/1000 is already quite low.
Assuming that the Oly engineers put about as much total energy capacity
as they could in the physical package, a flash delivering high effective
flash power at 1/2000 sec. would be quite large, probably bigger,
heavier and more expensive than a T45.
The other thing you would run into with this kind of solution for your
particular problem would be distortion of the image. Remember those old
pictures or early race cars where they seem to be leaning forward to go
faster? That is image distortion from the focal plane shutters on the
old Speed Graphic 4x5" cameras. Those big, heavy shutter curtains moved
so slowly that the image of the car literally moved on the film during
the exposure enough to obviously distort the image. The photographers
were careful to hold the camera so the distortion made the cars lean
forward. the other possible rotations lengthen, shorten and make the car
appear to lean back, visually like it is trying to hold back. The other
effects are also visible in other old photos of fast moving objects.
Even if you found a super high power FP flash on a camers with very high
FP speeds, you would still have a distortion problem at hummer wing
speeds. The solution to hummer photography with focal plane cameras is
high intensity, short duration flash that largely overpowers ambient
light on the bird itself (lit background is fine, if properly balanced).
Cameras like the OM2000 with vertical shutters have higher sync speeds,
and thus less problem with ambient light, mostly because the shutter
curtains only have to travel 2/3 as far as horizontal curtains, so it
takes less time.
Another solution to this particular problem is cameras with radial leaf
shutters in the lens. This allows x-synch at any speed, so the
flash/ambient ratio can be controlled with shutter speed. Since the
major exposure comes from a very short duration flash, the fact that
these shutters rarely even meet their maximum speed of 1/500 sec. is no
problem. This is generally the domain of in lens shutters on MF and LF
cameras. I'm pretty sure I've seen where someone mounted a large size
shutter in front of a 35mm SLR lens for some purpose or other. Not hard
to do, but an awkward setup to operate, unless a dedicated camera body
were to have its curtains disabled to leave then open all the time. A MF
camera with appropriate leaf shutter lens sounds easier.
Moose
Matt
At 15:36 27-04-03 -0500, Skip Williams wrote:
Yes, it pulses during the exposure in Super FP mode. The flash duration is
20-40 milliseconds. That way as the slit window passes over the film, the
flash is putting out essentially continuous light. Also, a Super FP flash
pulse is triggered when the first curtain is released, whereas normal flash is
triggered when the first curtain completes it's opening. If you shift to
normal OTF flash, the duration is cut to 25 microseconds to 1 millisecond.
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