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Re: [OM] new to the list/ precision of metering-dial 2S, 4 Ti

Subject: Re: [OM] new to the list/ precision of metering-dial 2S, 4 Ti
From: epozar@xxxxxxxxx
Date: Thu, 05 Aug 1999 21:57:49 +0200
> 
> My questions - open since a long time - are around the precision of the
> metering displays or metering-process of 2 S and 4 Ti:
> 
> 1. The display of my 2 S does not reproduce alterations of every 1/3-stop
> when using the plus-minus-dial; the first 1/3 sometimes none, the second
> 1/3 stop gives some alteration of the dial, sometimes one, sometimes the
> given two 1/3s at a time.

> Years ago I sent the camera to Olympus Hamburg and got it three times
> back with irritating comments.
> First time they charged about 300 DM for repair, but no result concerning
> the mentioned problem. After two times of sending back and pseudo-repair
> I gave up, after being successfull reducing the bill.
> After an encounter with another item of this type owned by a collegue I
> recognized the same behaviour (she had not ´til then and wisely did not
> care afterwards either).
> Is this a ?normal? abnormalty for this type? My OM2 N (unreliable too,
> mirror locks up unpredicticably as if batteries were low) as well as the
> 4 Ti work correctly in this regard.
> 
> 2. Spot or cw-mode - another but only technical aspect: My OM Ti
> announces usually 1/3 stop lower in spot-mode than in CW-mode (in Auto as
> well as manual), of course metering an absolutely even lighted object
> (wall f.e.).


Hi Hans,

IMO, this phenomena is quite normal. On Spot, only a central, *the
lightest* part of the image is measured. This value is OK for both open
and closed/working aperture.

On Average the value presented to the photographer is OK for the open
aperture but is usually one or even two thirds of an f-stop less than a
true speed for the closed/working aperture. This is because the system
measures (via a secondary mirror) both a central and peripheral parts of
an image - and the later are usually darker at the open aperture -
inflicting a "drop" you noticed.

You may ask why the problem is not present on other camera systems? I
believe that this is because Olympus (*complicated*) measuring system is
not much center weighted (as opposed to others) for it's "part
curtain/part OTF" style of real-time light measuring, e.g. pre-exposure
reading and pattern must closely match real-time values.

Try this: remove the lens, put a piece of paper instead (for a true
uniform illumination) and note if you have any difference between the
two measuring patterns. In my case they are the same. Or you may compare
the same through the closed_down lens (at the working aperture) - say,
50/1.8 at f5.6.

Thus in case of the lens with much light fall_off there will be more
difference between the two measuring patterns and vice-versa.

Finally, there is a potentiometer for just this purpose so the qualified
serviceman might adjust the readings to your taste. As delivered Olympus
cameras are set to be "right" at the open aperture and I believe this is
correct. If you want uniform readings
for both metering patterns one will ask: for what lens? Some lenses has
more light fall_off (commonly but incorrectly called "vignetting") and
others less..


-- 
Regards,

Emil Pozar
epozar@xxxxxxxxx
http://mypage.at/emilpozar


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