From: "Curtis P. Hedman":
> > As to the Program mode on the 2S and PC, I have
> > almost no clue, though I think (if I understand the instruction books) I
> > still get real time OTF exposure control.... >>
1. Yes, you do get OTF in Program mode on the OM-2S / OM-2SP:
In Program mode, the aperture value is calculated from the reading taken just
as you press the shutter, when the semi-silvered mirror and the Fresnel
mirror are still down, reflecting the light off the Fresnel mirror onto the
silicon photocell below.
After the mirror is raised, the shutter blind reading is taken and the
shutter speed set, compensating for any imperfections in the original
aperture reading - by altering the shutter speed if needed, I guess.
Presumably for longer exposures than about 1/30 second, the light reflected
off the film is monitored and the shutter closed when needed, as with the
OM-2(N), OM-4(T,Ti) and OM-2S OTF Auto modes. How cool! ;-)
There is a bit about the OM-2S Program mode in Vision Age magazine number 3,
if you ever see it.
2. It also talks about OTF Auto and OTF Program flash modes on the OM-2S. OTF
Program flash prevents possible underexposure which can be caused by setting
too small an aperture. It looks like the program mode selects an aperture
before the flash fires, depending upon the ambient light reading, and then
sets it and does the OTF flash routine to get the right flash exposure - this
looks likely to give you a better rendition of any ambient light level there
is, like a sunset sky for instance.
3. In spot auto mode on the OM-4Ti, there is no OTF because the light
readings are from the spot readings and they are not modified once the
shutter is released. I used to wonder is there was any modification by OTF,
but it looks like there isn't. From the diagram on page 6 of VisionAge
magazine 1 on Peter Gilbert's brochures site, the spot system and OTF
(average metering) system are pretty much separate, using separate sections
of the silicon photocell.
4. In MEMO mode on the OM-4(Ti), the readings from the previous exposure are
just held across to the next exposure(s), so if you have MEMO engaged there
is no OTF for subsequent exposures. You can use MEMO mode to remember an
exposure which was made/calculated from OTF Auto or Spot/Mulit-Spot mode, but
it is just fetching that exposure from the memory unmodified when you make
the subsequent exposures.
I hope that helps!
Dave Bellamy.
http://members.aol.com/synthchap/
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