Exactly
_________________________________
John Hermanson
Camtech Photo Services, Inc.
21 South Lane,
Huntington, NY, 11743-4714,
631-424-2121, www.zuiko.com
_________________________________
----- Original Message -----
From: "Moose" <olymoose@xxxxxxxxxxxxxxx>
To: <olympus@xxxxxxxxxx>
Sent: Wednesday, August 25, 2004 4:39 PM
Subject: [OM] Re: om4ti, continuous shutter speeds?
> Luca A. wrote:
>
> >I doubt that the modern AF SLR can do that, since the exposimeter receive
> >light froma semitransparent mirror. Only the flash exposimeter is
exposed
> >(sorry for the repetition) all the time long to light.
> >
> I can't speak for other brands, although I believe they work in a
> similar fashion, but what you say is not true of the Oly TTL-OTF bodies.
> In the case of the OM-2sp, 3, 4 and PC, a reflector below the partially
> silvered part of the mirror reflects light to a sensor assembly on the
> bottom of the mirror box. This provides the input for the exposure info
> shown in the viewfinder. In Auto mode, the same light sensor now "sees"
> light from the film plane and takes a quick reading off the first
> curtain when the mirror has gone up prior to actual exposure. If the
> needed exposure is 1/60 or less, the 1st and then 2nd curtains are
> released to create the traveling slit to give the correct exposure. If
> longer, the 1st curtain is released and the system continues to read
> light off the 1st curtain and film itself until sufficient exposure is
> reached, then releases the 2nd curtain.
>
> The mirror with sub-mirror and sensor on the floor of the mirror box set
> up on my Can*n 300D looks very similar and I suspect that it operates
> similarly.
>
> Roland Ruehl wrote:
>
> >Unfortunately I do not own a 4. But I have always wondered how
> >off-the-film measurement (and dynamic speeds) works together with
> >multi-spot measurement. Say, for example, you have defined two spots,
> >and then during a long exposure, the spots change light differently,
> >what happens ? Does the camera simply perform an overall level adjustment
?
> >
> Spot metering on the OM3 and 4 series is TTL, that is, the measurements
> are taken through the lens, but not OTF, light changes are not measured
> off the film during exposure. In Spot mode, the (average) exposure from
> the chosen spot(s) is calculated, a shutter speed (stepless) is
> calculated and that speed is used for the exposure. This is not only
> technically much easier, but truer to the purpose of spot exposure
> metering. If I measure a spot nowhere near the center of the subject
> frame, I don't wnat that reading/setting changed by relationship of the
> overall brightness of the subject frame relative to the overall
> brightness of the frame that happened to have the spot I chose to
> measure at its center.
>
> Moose
>
>
>
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