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

Subject: [OM] Re: OM-1 mercury cells / adapter / recalibration
From: Tim Hughes <timhughes@xxxxxxxx>
Date: Tue, 19 Apr 2005 04:57:14 -0700 (PDT)

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:


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.


Tim Hughes

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