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Re: [OM] OM-2S Shutter Firing Sequence

Subject: Re: [OM] OM-2S Shutter Firing Sequence
From: "Carlos J. Santisteban" <zuiko21@xxxxxxxxx>
Date: Wed, 24 Mar 2010 23:43:13 +0100
Hi Ken and all,


From: Ken Norton (kenzone-10.com)>What exactly is the shutter firing
sequence for the OM-2S and is it >different between Program Mode, Aperture
Priority Mode and Manual Mode? I'm no expert here, but I can share what I
*think* it does... >Here is what I THINK happens in Program Mode-- >please
correct. I'm eager to know also... >1. Shutter-release is pressed. >2.
Aperture actuator arm in camera closes down lens to >smallest F-Stop allowed
by len's aperture ring I don't think so. You can check it by shooting in P
mode without lens: if the camera is pointing towards a bright light, the
aperture actuator arms moves almost in full, trying (in vane) to stop down
the lens... but in dim light, that lever almost doesn't move at all, because
the Program tried to select the widest available aperture!AFAIK, P mode is
OTF auto with a partially stopped down lens. Viewfinder readouts are, as
always, orientative only ;-) >3. Mirrors swing up Again, I can't tell for
sure, but I think this is an independent movement, maybe somewhat delayed
from the aperture lever. On "classic" OMs (1/1n/2/2n), if you hold the
aperture lever while shooting, the mirror WON'T go up... and if you hold the
mirror instead (e.g. with a Q-tip) the aperture lever will go fully up, but
the shutter won't open until the mirror is (almost) up. OTOH, if you hold
the aperture lever on the OM-2S, "nothing" happens -- the mirror will go up
anyway and the shutter will open. If I shoot with my sluggish 50/1.2 on a
classic OM (stiff aperture pin) there is a noticeable lag when shooting...
but on the OM-2S, it will shoot as always but the iris may not stop down on
time, leading to overexposure :-( >4. Exposure reading begins As always in
OTF modes. >5. If in Program Mode, the aperture actuator arm adjusts to new
F-Stop. Read my previous paragraph... >6. Curtain Opens >7. Film Exposed >8.
When sufficient light has hit film, Curtain Closes >9. Mirrors return to
down position. Usual sequence for OTF auto, I think it's OK in P too. >Here
is what I THINK happens in Aperture Priority Mode--please correct. >1.
Shutter-release is pressed. >2. Aperture actuator arm in camera closes down
lens to the F-stop set on the >lens. >3. Mirrors swing up >4. Exposure
reading begins >5. Curtain Opens >6. Film Exposed >7. When sufficient light
has hit film, Curtain Closes >8. Mirrors return to down position. I agree in
full. >Here is what I THINK happens in Manual Exposure Mode--please correct.
Againm I think it's correct. >It is my screwed up understanding that the
main difference between the OM-2S >and the other OM bodies is that the
Aperture actuator arm is activated >BEFORE the mirror goes up, Maybe. The
aperture actuator is definitely slower (and smoother) than other bodies. Not
sure if the mirror moves slower too. >whereas on the others it goes up
either at the >same time or just after the mirror goes up. It does start
moving before the mirror. It's the aperture actuator what pushes the mirror
up, but thru a spring -- you can keep the mirror down even with the actuator
lever up. In any case, what starts actual exposure is the position of the
mirror, regardless of aperture actuator. >The sequence of events with the
>OM-2S is definitely longer than that of the OM-3Ti and OM-4Ti and induces a
>substantial shutter-lag as a result. Absolutely. That's why they won't go
over 3.5 fps with Motor Drive (vs. 5 fps). But it also makes the thing way
smoother. Some wonderbricks have really smooth firing actions, at the
expense of a noticeable shutter lag (e.g. Contax Aria) I think the OM-40/PC
(the other OM with P mode) has a similar aperture mechanism -- good for 3.5
fps only.
I hope someone enlightens us soon... Cheers,
--  Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
-- 
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