Archived posting to the Leica Users Group, 1998/03/10

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Subject: Re: [Leica] M6 question
From: thai pham <phamt@yahoo.com>
Date: Tue, 10 Mar 1998 12:55:24 -0800 (PST)

- ---COLBYG@ULV.EDU wrote:
> It behaves the same way: shutter uncocked, depress shutter release
and flash fires...
> ..
> to determine if any speeds also synchronize?
> > >>        Is this normal?  And, if merely depressing the button
(without the
> > >>shutter moving) fires the flash, how can the flash "know"
exactly when to go

With regards to flash going off with the shutter uncocked, it is quite
normal and happens to all leica m's.  

I tested the synch with speeds from 15 to 50 (flash synch) and they do
work.  Above 50, you will see the picture partly blinded by the
shutter screen. 

The leica m shutter works this way:  first,  a left shutter screen
goes from left to right, thus opening a gap letting the light to the
film.  The right shutter screen then goes from left to right, thus
closing that gap.  When the shutter is cocked, the flash synch is
triggered by the left shutter screen hitting a contact on the left
side.  At speed below 1/50 the two screens open a gap as wide as the
film width (36mm), thus you have complete lighting on the exposed
area.  At higher speed, the opening gap is smaller than the 36mm of
the exposed film area, thus you get partially lit film.  This gap
travels the whole range of the exposed area so you have complete
exposure with constant light.  Flash light is about 1/5000 sec, so
only a portion of exposed area get light at shutter speed higher than
max synch speed.  This is hard to explain without a diagram, hope you
get it.  Anyway, synch works for all speed below 1/50.
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