: I think I need to get back to basics a little, as I don't think I fully
: understand the technicalities of the different systems !! For example, I
: hear the terms TTL and OTF used a lot, and know (I think) that they stand
: for "Through The Lens" and "Off The Film" respectively. As I understood
it,
: the OM's had 2 metering systems running side-by-side. One measured light
: through the lens to give you the original reading (TTL) and the other took
a
: reading of the light reflected off the film during exposure (OTF). Is
this
: correct ? I heard somewhere that one of these (OTF) only applies in Auto
: mode ?
All OM bodies do their available light readings TTL, meaning that any
extensions and filters are taken into account, opposed to cameras that have
their sensors on the outside next to the lens.
The OM-1(n) and also the OM-2(n) in manual mode do their reading from the
focusing screen. This is the reason why the clear field focusing screens
don't give correct readings in these cameras (for the OM-2(n) in manual
mode).
The OM-2(n) in auto mode reads available light OTF, which really means off
the curtain (which has the special pattern) with shorter shutter speeds and
off the film with longer shutter speeds.
The OM-4(Ti) and OM-2SP also do their auto reading OTF, but the manual
reading is done from a sensor beneath the transparent mirror. This also
applies to the OM-3(Ti). Thus these models always give correct readings with
any focusing screen.
: These bits I have almost come-to-terms with, but I really don't get quite
: how they apply to Flash Photography. Obviously the meter reading before
the
: shot is taken would tell you how much flash is needed, but does the OTF
bit
: read the amount of light and tell the flash when to turn off ?
The OM-2(n), OM-SP, OM-4(Ti), OM-3Ti and OM-40 (PC) can control the T
flashes OTF. The reading before the flash is triggered is only used to
determine if the flash should be triggered at all (shorter as 1/60 -> no
flash). If the flash is triggered, the sensors aimed at the film read the
reflected light and a signal is sent to the dedicated flash when enough is
received. This is why these cameras have a third pole in the hot shoe,
compared to the OM-3, OM-10, OM-20 and OM-30 that don't support OTF flash
(only OTF available light).
: One area of a little confusion to me is the FP / X switch on the side of
the
: camera. Does this simply switch between the hot-shoe contact and the
socket
: on the side of the camera, or does it switch between different flash types
?
: If so, are both X and FP (whatever they are) available from both the hot
: shoe and the socket ?
X is for normal flash bulbs and electronic flash, FP for long burning (Focal
Plane) bulbs that needed to be ignited right before the shutter opened. On
the OM-1 and OM-2 the switch controled both the pc outlet and the hot shoe,
on the OM-1n and OM-2n it only controls the pc connector - the hot shoe is
always X. Electronic flashes are not synchronized in the FP mode, so special
care is needed with the non-n models and the flash in the hot shoe.
hnz
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