On Mon, Jul 22, 2002 at 08:13:12AM -0000, CyberSimian wrote:
> ----- Original Message -----
> From: "Tom Scales" <tscales@xxxxxxxxxxxxxx>
> Sent: Saturday, July 20, 2002 5:57 PM
> Subject: Re: [OM] Fill-in Flash with Olympus Flashguns
>
> > I'm not sure your conclusions are correct.
>
> I am not convinced that they are correct either, which is why I listed them
> in my previous post! The problem is that I cannot see how the F280 can
> possibly do accurate fill-in flash, as it does not have enough information.
> Let's consider an example.
Well, it is part of the OTF-philosophy, that the comera need`s no other
information than the film sensivity. The only thing the OTF-system can do
is meassuring. And it says "Stop" when enough light has exposed the
film. The trick is to messure the light, when it is exposing the film.
So you don`t care about distance, apperture, shift, ... effects, you`re
simply meassuring the light which passes all uncertainties.
>
> Suppose you have an OM4Ti set on "Auto", with an F280 connected, powered-up,
> and set on "Super FP". You adjust the aperture so that the ambient light
> gives a shutter speed of 1/125 or faster. You press the shutter button, the
> mirror flips up, and the OM4Ti meters from the first shutter curtain. What
> happens next? Well it seems to me that there are two possibilities:
IMHO, it is much easyer:
1.) Mirror flips up,
2.) The OM4 trigges the F280, imediatly before OTF-metering starts on the 1st.
curtain,
which is then giving a constant output of light during the exposure.
3.) The OTF-system is meassuring the combination of flash and ambient light.
4.) When enough light is registered the second cutrain starts to close.
5.) when the second curtain has closed, the flash can be turned off.
If the exposure was shorter than 1/30sec. there is some energy left in the
capacitor.
This System can only care to get a correct exposure. But can`t balance anthing.
Because the ambient an flash light work together, there is a fill in effect,
because
exposure done by ambient light is cut off the flash amount.
The ratio flash-ambient light depends on the brightness of the scene and the
flash to object distance.
I´d like to have a zoom-reflector for the F280. The only way I see, to
influence
the fill-in-ratio is to use a ND-filter (handkerchief) in front of the flash,
when you can`t change the distance.
> In "Super FP" mode, the
> camera cannot vary the duration of the flash; instead the camera must vary
> the power (full, three-quarters, half, quarter, ....). Can the F280 choose
> what flash power to use in "Super FP" mode (as distinct from flash
> duration)?
I don`t think so. would be nice, but the F280 in FP has not that much power
that splitting is that necessary. :-(
It is sad, that Olympus didn`t develop the FP technique further.
> So my conclusion is that the F280 designers studied thousands of fill-in
> flash scenarios, and decided on a flash power (guide number 28) that gives
> the right amount of fill-in for the average case, and a result that is
> better than no fill-in for cases that are not too different from the average
> case.
The FP-flash guide number decreases to 16 (metric) at 1/60 second. At faster
speeds it decreases the same way, you`ve to open the apperture. So the flash
reach (or fill in ratio) stays the same.
I guess the F280 designer were happy when it worked at all.
My suggestions to F280 users:
1.) A test series in fill in situation (sunlight), and then approach the
object. As the object come
closer, the share of flash should increase, until you get a almost flash only
exposure.
2.) The same test series with less ambient light should also increase the
flash amount,
compated to the same distance in the first series.
When you use the memory mode (clear between shots) you can compare the
expected shutter speed indicated before the exposure, and the really used value
influenced by the flash, which is stored after the exposue.
(P.S. This is my idea how OM-4 memory mode works without spot)
Hmm. I nedd that equipment to ty myself.... :-(
Frieder Faig
sunlight,
> But I am happy to be corrected!
>
> -- from Cy in the UK
>
>
>
>
> < 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 >
>
< 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 >
|