My idea of the light measurement method of the 4Ti come from the fact
that, at auto mode my 4Ti is 2/3 stop to 1 stop under (depends on the
film used) just at ss below 1/60s, it possess the same error rate up to
1/4s. At 1/60s or above there is no different between displayed speed
and memorized speed (actual auto exposure speed).
The different in behaviour is very clearly separated at 1/60s. This also
happen on at least one other 4Ti at OM service center Hong Kong where
the technician in-charge shown me.
C.H.Ling
John Hermanson wrote:
>
> The cell which gathers light for otf has an output whereas cds cells change
> resistance based on light. The OM-4 cell gathers light from the first
> curtain/film
> unitl the circuit reaches a quench point for 18%. This is when the magnet is
> released (it had been preventing the 2nd curtain from moving) and the second
> curtain enters the film plane.
> Very bright light quenches the cell quickly so you have high shutter speed up
> to
> 1/2000.
> Low light takes longer to quench, so you have a long shutter speed.
>
> I don't think the circuit waits if it is low light or the ss is below 1/60,
> the ss
> is computed in real time as it is happening, whether it be 1/63 of a second or
> 1/40th.
>
> John
>
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