Olympus-OM
[Top] [All Lists]

Re: [OM] full-aperture metering; video converter lenses; serial numbers

Subject: Re: [OM] full-aperture metering; video converter lenses; serial numbers
From: Jay Maynard <jmaynard@xxxxxxxxx>
Date: Fri, 14 May 1999 10:28:30 -0500
On Fri, May 14, 1999 at 04:57:12AM -0700, William Sommerwerck wrote:
> I'm more than a little irritated about the negative responses to my correct
> explanations of full-aperture metering.

Perhaps we're really in violent agreement here...

> A bit more thought shows that there is another way to take full-aperture meter
> readings. Instead of placing the aperture-position pin at a particular f-stop,
> you can reposition it to compensate for variations in the lenses' maximum
> apertures. Minolta was probably the first company to do this, and it's the
> system OM cameras use.

Let me approach this from a different direction.

Looking at the back of a 50/1.4 and a 200/4, when the aperture of both
lenses is set to wide open, the aperture coupling lever inside the lens
mount is in the same position: diametrically opposed to the lens mount index
stop (the little screw that stops the lens from turning any farther in the
mount at the correct position for the mount latch to engage). Now, this says
that all the meter cares about is how much less light there will be at time
of exposure,  or else the coupling lever would be at different positions for
the two lenses. Put another way, the 50/1.4, when set to f/4, has its
aperture coupling lever in a different position than that of the 200/4 when
set to f/4.

I have two teleconverters, a Sigma and a Zykkor. In both cases, when the TC
was mounted to the back of the lens, the aperture coupling lever wound up in
the same position as it did on the lens without the teleconverter.

Both of these observations tell me that the meter takes care of different
lens speeds by ignoring the question entirely and letting the actual amount
of light passing through the lens do the work for it. It will see three
stops less light through the 200/4 than it does through the 50/1.4, but
that's exactly the effect needed to produce the correct exposure, since the
aperture coupling lever is three stops closer to the wide open end of the
scale. A 2X teleconverter will darken the image in the viewfinder by 2
stops, even wide open, so the meter will automagically do the right thing
even though it hasn't been explicitly told you went from a 200/4 to a 400/8.

I think I may be saying the same thing you did in the paragraph I quoted
above...if not, where am I going wrong?

--

> The first time I saw this 12345xxx format for serial numbers was in ads for 
> used
> Leica lenses. The reason? You don't want to publicize "real" serial numbers so
> that dishonest people can use them to make fraudulent insurance claims.

The first time I saw this kind of thing was in ads for guns. It was
explained that there had been several cases of people using the information
to claim that the gun in question had been stolen, and to actually try to
"recover" the gun from the advertiser.

< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >


<Prev in Thread] Current Thread [Next in Thread>
Sponsored by Tako
Impressum | Datenschutz