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[OM] Re: OM-1 mercury cells / adapter / recalibration

Subject: [OM] Re: OM-1 mercury cells / adapter / recalibration
From: "John Hermanson" <omtech@xxxxxxxxx>
Date: Tue, 19 Apr 2005 08:31:29 -0400
I'd say 98% of the time, when I adjust the meter to BV (Brightness Value) 12 
(which is asa 100, f5.6, 1/125th sec.), the meter is also spot on at BV 15 
(asa 100, f5.6, 1/1000th) .  When it is off at BV15, it is because the cds 
cells have gone bad.

John Hermanson
Camtech Photo Services, Inc.
21 South Lane, Huntington, NY, 11743-4714,
631-424-2121, www.zuiko.com
Olympus OM Service since 1977
----- Original Message ----- 
From: "Tim Hughes" <timhughes@xxxxxxxx>
To: <olympus@xxxxxxxxxx>
Sent: Tuesday, April 19, 2005 7:57 AM
Subject: [OM] Re: OM-1 mercury cells / adapter / recalibration

> Chuck wrote:
>>>My recollection is that the meter can be off by a small amount at the 
>>>extreme ends of the brightness range. Tim Hughes has written extensively 
>>>on this in the archives in his quest to develop the perfect silver oxide, 
>>>mercury battery simulator. (I didn't want to call it an ordinary 
>>>adapter). Maybe Tim will weigh in here.<<
> Chuck is right, the diode mod or MR9 adapter can be a little bit off at 
> high EV's (~0.3EV) but the error drops off rapidly at lower EV's. I 
> believe when John does the diode adaption as part of a CLA, he usually 
> fine adjusts the high EV cal end point (mech setting) which helps a bit 
> depending on diode, but there is some small non-linearity left at the EV's 
> just below full scale.
> Here is probably more detail than you want summarising my old posts:
> http://olympus.dementia.org/Hardware/PDFs/OM1DiodeVer2_1C.pdf
> There is actually a much better way of doing this acurately without a 
> diode, which I have not put on the web. In fact, I think Chuck has done a 
> few of his cameras that way based on a description I sent him.
> Regards,
> Tim Hughes

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