I suspected as much, but thought I'd ask anyway. Thanks for your detailed
explanation.
clintonr@xxxxxxxxxxxxxxxx wrote:
> FAB -
>
> In short, no.
>
> The OM-1's meter uses two CdS (photo-resistive) cells on either side of
> the eyepiece, "looking" into the back of the prism just like you do when
> you're focusing. They register the light level at the focusing screen.
> There's no space to insert any sort of optical device to concentrate
> their focus on the center of the screen, and simply covering them with
> some sort of Waterhouse stop (a plate with a hole in it) would only have
> the effect of reducing the amount of light that reaches the cell, giving
> an erroneous reading.
>
> Those cameras with true spot metering capability usually use amplified
> photo-voltaic cells which are manufactured with a large "average" zone
> around a small "spot" zone in the center of the cell. Light from the
> film plane is then focused onto the cell. These two zones function
> independently of one another, giving one reading for the very center of
> the frame and another for the rest of the frame.
>
> Spot meters that _do_ use CdS cells usually have an optical arrangement
> to provide the spot effect - like using a telephoto lens, as mentioned
> elsewhere.
>
> Franklin A. Berryman wrote:
> >
> > This is a technical question probably best answered by John H., but here
> > goes:
> >
> > Is there anyway to modify an OM-1/1n to reduce the area the meter reads so
> > that
> > it spot meters? As I understand it, the meter is center weighted and reads
> > off
> > the pentaprism. Anyway to reduced the angle of view so that it meters off
> > a
> > just the microprism area?
> >
> > Here's hoping...
> >
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