Re: [Rollei] TLR Meter

["Richard Knoppow" <dickburk >]

- ----- Original Message ----- 
From: "Kotsinadelis, Peter (Peter)" <peterk  >
To: <rollei  
Sent: Wednesday, April 23, 2003 2:44 PM
Subject: [Rollei] TLR Meter


>
>
> Is there any simple way to adjust the meter on a TLR?
>
> I have 3 TLRs with built-in light meters (Gossen Cell) and
only one is
> accurate (and surprisingly accurate at that).
> The other two are off about 1-2 stops.  I know I can
adjust ASA but is
> there an adjustment to the meter itself to increase its
output to the
> needle movement.
>
> Peter K
>
  I think all Rollei meters are Selenium cell types. If the
cell goes bad there is no way to compensate it because the
error varies with light level. The usual symptom is that it
reads low at the high end of the scale. The only fix is
replacing the cell.
  The error is generally on the order of one to two stops.
  You can check a Selenium meter against itself providing
the two light ranges overlap. With light which will register
on both ranges the reading should be the same or at least
very close. If the cell is gone it will read low on the
range where the reading is at the high end of the meter
scale (brighter light on the cell). Where this test is
difficult the meter should be checked against a known good
meter at low and high readings on the _same_ scale range. If
the cell is bad the readings will be compressed at the high
end.
  If the error is _constant_ it suggests the meter movement
is not zeroed correctly or there is some mechanical problem
with the linkages in the camera.
  The failure mechanism in Selenium cells seems to be either
the entry of moisture into the cell or some change from
heat. I think the actual cause of the nonlinear reading is a
change in the internal resistance of the cell.
- ---
Richard Knoppow
Los Angeles, CA, USA
dickburk  

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