It's not really that complicated. There are only 4 Om bodies that do
Auto TTL OTF with T series flashes, OM-2, OM-2n, OM-4(T(i)) and
OM40(PC). All of them work the same way in that mode except the
original OM-2.
When a T series flash set in full power Manual Mode is attached and
charged, they all set a minimum shutter speed of 1/60 sec. Any time the
Auto exposure system selects a speed of 1/60 or below, the camera
actually fires at 1/60, the flash fires and is controlled by the OTF TTL
curcuit, which quenches the flash when sufficient exposure is reached.
When the Auto selected speed is over 1/60, the flash does not fire, as
the whole film frame is never completely uncovered at once by the
travelling slit of the shutter, so proper flash exposure is not
possible. As Piers says, the way to be sure that the flash will fire is
to have the viewfinder show a speed below 1/60 (max of 1/30 second on
the OM40 and OM-2n and 1 diamond below 1/60 on the OM-4 series). You
can, of course set any even slower speed to use a smaller aperture
setting, as the shutter will actually fire at 1/60. The only limits are
distance and flash power.
Moose
Michael Kopp wrote:
>At 23:24 +0100 3/9/04, Piers Hemy wrote:
>
>
>>Why 1/30? Because the actual shutter speed selected by the camera in auto
>>mode is not a fixed value - but the viewfinder *is*, being the nearest to
>>the actual. The actual speed selected for a 1/60s indication could be
>>1/80s, which would not give a full frame flash exposure (and thus, by
>>design, does not fire the flash) but it could be 1/50s, which would be OK
>>(and the flash would fire). With an indication of 1/30s, you can be sure
>>the actual speed will be below 1/60s, hence my phraseology - 1/60s might
>>work fine, but it might not!
>>
>
>Well, you could be saddled with having to work for a living with
>Nikon D70 and D1H cameras and Nikon flashes from the SB-80 to the
>SB-600 and -800 ...
>
>I STILL haven't figured out all the modes and "features" and
>idiosyncracies, despite -- or perhaps because of -- the hundreds of
>pages of manuals.
>
>One literally has to learn their programming, then build one's own
>framework of practice around it.
>
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