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Re: [OM] OTF light metering w / 280 Flash

Subject: Re: [OM] OTF light metering w / 280 Flash
From: "Peter Loggie" <peter_loggie@xxxxxxxxxxx>
Date: Thu, 24 Sep 1998 19:47:43 PDT
In line with Pauls question, if the only signals being sent to the F280 
flash are merely when to start and to stop firing what is the purpose of 
the different pins in the connectors, and why is a different number 
required than for the T32?

Peter Loggie

>From: Pauls0627@xxxxxxx
>Date: Thu, 24 Sep 1998 14:26:53 EDT
>To: olympus@xxxxxxxxxxxxxxx
>Subject: Re: [OM] OTF light metering w / 280 Flash
>Reply-To: olympus@xxxxxxxxxxxxxxx
>
>I've been trying to get this full synchro flash stuff (and OTF flash in
>general) straight in my head (trying to convince myself to trade in an 
OM-4
>for a -4Ti, I guess!). Someone correct me if I'm wrong here:
>
>OTF Flash (OM-2n, OM-3Ti, OM-4, OM-4Ti):
>
>1. First curtain begins to open, meter starts accumulating exposure off 
of the
>film and curtain
>2. First curtain fully open - Flash fires
>3. Meter quenches flash and starts closing the second curtain when 
sufficient
>exposure is measured (or flash fully discharges)
>4. Second curtain closed - effective shutter speed 1/60
>
>I think step 4 is different for the OM-2 (not the -2n) in that the 
shutter
>will stay open as long as necessary to achieve sufficient exposure, 
even if
>the flash power was insufficient.
>
>Full Synchro Flash (OM-4Ti):
>
>1. First curtain opens, flash begins discharging, meter starts 
accumulating
>exposure off of the film and curtain
>2. When sufficient exposure is achieved, meter triggers the second 
curtain to
>begin closing, flash continues to fire
>3. Flash stops when the second curtain is closed
>
>I assume the OM-77 handled full synchro flash the same way
>
>Full Synchro Flash (OM-3Ti)
>
>1. First curtain opens, flash begins discharging
>2. Second curtain begins closing to achieve shutter speed selected on 
ring
>3  Flash stops when the second curtain is closed
>
>Notice that since the OM-3Ti's meter can't control the shutter, the 
F280 is
>acting essentially like a manual flash, therefore the need to do the GN
>calculations. In fact I don't think the OM-3Ti's meter is used at all 
during
>full synchro flash.
>
>I don't think it's possible for the camera to control the intensity of 
the
>flash based on an OTF reading, because it would have to adjust the 
intensity
>*during* exposure, resulting in different exposure on different parts 
of the
>frame as the shutter "slit" passes over the film.
>
>Since the output from the flash is constant, the only way to control 
the
>amount of fill flash is to vary the flash to subject distance (I 
think). I
>recall it was said here once that changing the exposure compensation 
dial on
>the OM-3Ti will provide varying fill rations. The way I see it, since 
the
>camera has no control over the flash other than to start it when the 
first
>curtain starts moving and stop it when the second curtain closes, 
changing the
>exposure compensation dial will only vary the total exposure, not the
>flash/ambient mix.
>
>Do I have this right?
>
>Paul Schings
>Coventry, RI
>
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