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RE: [OM] differences in f stops

Subject: RE: [OM] differences in f stops
From: "Malcolm Clay" <zuiko@xxxxxxx>
Date: Mon, 1 Apr 2002 00:24:14 -0600
> -----Follow-up Message-----
> From: owner-olympus@xxxxxxxxxxxxxxx
> Subject: Re: [OM] differences in f stops

> I also have a Tokina 28-70, it over exposed by around 3/4 stop in
         <snip> ...
> lens. All my other Zuikos does not have such problem (except the 28-48
> which also exhibits a bit strange).


Okay, somebody who knows better speak up and correct my misinformation...but
I thought the f-stop reading on zooms were either an "average" or at one
specific point on their zoom range -- due to the variable geometry of their
lens groups. (yes? no?)


> -----Original Message-----
> > <snip>switching between...an Olympus 200mm f4 and a Tokina 135mm f2.8.
When I got home,
      <snip>
> > ...found that the 2 lens register 1 1/2 f difference
> > for the same framing of the wall


So am I to understand that you varied the distance from lens to wall for
each lens to keep the area metered the same? Wouldn't this vary the light
fall-off? Seems like there is someone who is a pretty good physics tutor on
this list who can cast some light on this matter (pun intended)...



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