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Re: [OM] John's metering dilema

Subject: Re: [OM] John's metering dilema
From: Joe Gwinn <joegwinn@xxxxxxxxxxx>
Date: Wed, 1 Oct 2003 20:25:01 -0400
At 8:49 PM +0000 10/1/03, olympus-digest wrote:
>Date: Wed, 1 Oct 2003 12:22:41 -0300
>From: "John Hudson" <13874@xxxxxxxxxx>
>Subject: Re: [OM] John's metering dilema
>
>- ----- Original Message ----- 
>From: "Bill Pearce" <bspearce@xxxxxxxxxxxxx>
>To: <olympus@xxxxxxxxxxxxxxx>
>Sent: Tuesday, 30 September, 2003 07:20 PM
>Subject: [OM] John's metering dilema
>
>
> > Most of you that have spent some time on this list know that I consider the
> > incident meter to be the gold standard in at least 900f metering
> > situations. I am joined in this by virtually every commercial and industrial
> > shooter alive. The joy of the incident meter is that it compensates for
> > various situations that the reflected meter cannot, the most obvious being
> > highlight and shadow. The complex ttl meters in wonderbricks spend a lot of
> > time and trouble doing what the much more simple incident meter does
> > automatically. This makes me totally confused by John's situation!
>
>I had a lengthy phone call from "Mike" at Nortown Photo Service [authorized
>Canadian Olympus service / repair station where my OM4T went for CLA] in
>metro Toronto this morning.
>
>He advised me that the TTL metering system and shutter speeds had been
>accurately calibrated and set to original Olympus standards using Olympus
>supplied or authorized equipment. 

He thinks that because he went through the motions, pushed all the right 
buttons, it *must* be correct?  One uses that fancy equipment only to calibrate 
cameras in good repair.


>He also advised me that there was no
>comparison of the indicated output of those recalibrations with any other
>metering devices such as a Sekonic meter. He told me that I should choose to
>use one metering system or the other but not both! What seemed to go above
>his head was that the end product of using either one of the two metering
>systems, namely a properly developed negative or slide, should be
>identically exposed regardless of which metering systems was used.

Right you are.  All are supposed to implement the same set of ANSI/ISO 
standards to within something like a third of a stop (when new).  Walt Wyman 
reported that he couldn't get his cameras and lightmeters to differ by more 
than a half stop, which is exactly as expected.


>He tried to explain that the indicated metering differences between using
>the Sekonic and the OM4T's TTL system resulted from the differences in the
>colour temperature sensitivity of the light measuring cells in the two
>meters. Whether there is any substance to this statement is something beyond
>my knowledge and could perhaps be commented upon by others. My immediate
>feeling is that this is a bit of a bogus argument in the present case.

Probably bogus, but easily tested using some ordinary photo filters.  Use the 
two meters with various filters (including no filter) looking at some stable 
scene through the same filter, like the grass in your lawn near noon, or a 
white wall in sunlight.  Some color temperature correction filters would be 
ideal, but a red filter and a green filter ought to work.  If the two meters 
differ greatly in spectral sensitivity, then the difference between the meters 
will vary with filter color.  Be sure to run through the series twice, to 
detect if the scene brightness varied too much.  Or, do it all inside with 
artificial light.

Actually, testing first in daylight and later under ordinary incandescent light 
would also work, as the color temperature of daylight is 5500 K or so, while 
houshold incandescent lamps are more like 2900 K.  Photofloods are something 
like 3200 K.  This has the advantage of not needing any filters, and yet 
bearing directly on the theory that the color temperature matters.


>What I think has happened is that the linkage between the exposure
>information shown in the viewfinder does not match the actual shutter speed.
>For example, multi-spot metering shows an average exposure in the view
>finder of say 1/45 @ f16. When the shutter is fired the shutter actually
>fires at 1/125 @ f16 giving me a properly exposed slide. When I set the
>camera manually at 1/125 @ f16, which is the Sekonic reading, the shutter
>actually fires at ~ 1/375 @ f16 giving me an under exposed image.

Weird.  Is this a metering problem, or a shutter problem?


>If my Sekonic gives me properly exposed slides using an M3 I am confident
>that the meter is accurate. The fact that I cannot take my Sekonic's reading
>to my OM4T in manual mode tells me that the link between OM4T's indicated
>shutter speed is different from the actually speed with which the shutter
>fires. How does one get that line of thinking over to the CLA people!


Getting good slides is the only test that matters.  That's why we bother with 
cameras.  And lightmeters.  Everything else is intended to make that happy day 
more likely.

I think I would find another shop to do the CLA, and write this one off to 
experience.

Joe Gwinn 


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