Yes light fall off can cause interesting effects. I compared the exposure
measurments
of a 1.4/50, 1.8/50 and 3.5/50 Macro. Now I pointed them to a poster which is
average
grey enough, but surrounded with a white surrounding.
When I compared spot metering with averaged metering there was a 2/3-stop
difference
with the 1.4/50 and the 1.8/50. Averaged metering indicated less light. But
with the 3.5/50 M
there was no difference between spot and averaged metering of my OM2sp.
Now I think the 3.5/50 has less falloff, which increases the influence of the
white border.
Frieder Faig
On Thu, Sep 28, 2000 at 09:25:33AM +0800, C.H.Ling wrote:
> There is a simple answer, Olympus take care of the light fall off when
> lenses are wide open. In average you won't get one stop different from
> wide open to next stop of it.
>
> C.H.Ling
>
> wayneharridge@xxxxxxxxxxxxxxx wrote:
> >
> > Frieder wrote:
> >
> > > This is a strange effect, but it is exact what the meter does.
> > > >From F1.4 -> F1.2 the exposure indicator of my OM 2sp moves 1~1.5 Index
> > > >fields
> > > ( 1/3~1/2-F-stop) instead of 3 for a hole F-stop.
> > > This is caused due to the lever which is telling the camera how much the
> > > lens
> > > is stopped down. The marks between F 1.4 and F 2.0 are nearer together
> > > than the
> > > others which causes this difference. So it seems it is what the lens does.
> > > This phenomen is visible on every Zuiko I have. The first F-stop is not a
> > > whole F-stop ( at least one index missing). It is hard to guess why this
> > > is
> > > so and weather it affects the real speed of the lens?
> > > Seems exposure with internal meter should always be correct,
> > > but when working with a hand-held-meter?
> >
> > That's interesting !
> >
> > Also note that I measured exposure time with a stop watch (admitted, not
> > that accurate) from the auto OTF measurement made by the body. I should
> > really check this with some other lenses.
> >
> > ...Wayne
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