At 8:23 AM +0000 2004.02.15, James Royall wrote:
>Moose, is the graph you were referring to on this page?
>
>http://www.mir.com.my/rb/photography/hardwares/classics/olympusom1n2/om1/basic.htm
Thanks for this URL, which I hadn't seen before. It answers my question about
how centre-weighting is done in the viewfinder system -- the aspherical lens.
The graph is useful for visualizing how it works.
> So does this mean there are two methods
>involved; the aspherical metering element and prism, and the curtain
>meter pattern?
Yes. This was mentioned in earlier replies.
A comprehensive description (PDF file)
of how the two metering systems work can be found in a trouble-shooting
guide for 2n electronics at the hardware page maintained by Mark Dapoz
(there is a lot of interesting stuff there -- thanks Mark!). That's
http://olympus.dementia.org/Hardware.
>
>If center weighting exists in auto mode, it can't be from the pattern
>as it's off the film.
>
Because metering starts at the release of the first shutter curtain, some
of the light measured is off the curtain, the reflectance of which is
similar to film (somewhere in the archives I've seen posted the values for
different films). This is mentioned in Moose's reply as complicating
the design of a centre-weighted OTF system.
regards
Andrew
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