Having used a T-20, T-32 and F280 on an OM-4 I have had much less trouble
using TTL/OTF control than using the "Normal Auto" mode on the T-20 or T-32
(the F280 does not have this mode). Using a GN is more accurate, however
this presumes you have enough time to calculate the aperture from the
distance. For candid indoor work with flash, I do not often have this time
nor can I control the environment (as in a studio). The T-20 and T-32 both
have the sensor in the "O" of the "Olympus" on the front of the flash.
This has worked OK for me when mounted on my OM-10 body most of the time.
However the sensor can be fooled by a bright light source (bright lamp or
window with bright daylight streaming through) within the field of view of
the flash sensor. The TTL/OTF mode when used on my OM-4 is not affected
nearly as much by these situations. I shoot Kodachrome 25 & 64 and have
not had any real problems other than the "Normal Auto" mode flash sensor
being fooled under the cited conditions. I also tend to keep fresh
batteries in the flash units if for no other reason than keeping the
recharge time down. Batteries are relegated to the winder or other uses
when the recharge time starts to noticeably increase. This might be why I
have not encountered the inaccuracy phenomena cited with low batteries.
-- John
P.S.
I have a three different Sunpak flash units, the sensors on which can be
fooled as well by a bright light source . . . so my limited experience
tells me this is a problem with auto sensors on flash units in general.
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