At 22:32 1/29/00 , Joseph wrote:
>Isn't light is travelling through the lens whenever the lens cap is off
>regardless of whether it is hitting the front of the shutter or the
>film with a leica rangefinder? Leica's have focal plane shutters,
Just like water in a pipe, photon flow is controlled by a valve, in this
case a shutter curtain. If the shutter is closed in an RF, it stops the
flow just as in a pipe. There's noplace else for it to go. However, in an
SLR when the shutter is closed, the mirror is down allowing continuous flow
off the mirror through the prism and out the viewfinder.
This brings to mind a preventive measure that can be used by OM-1[n] owners
to slow down the wear process, the MLU. Simply flip up the MLU when the
lens cap is off and not taking a photograph. This blocks the other path of
photon flow out the viewfinder.
-- John
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