At 08:30 8/3/02, Joel Wilcox wrote:
At 08:15 AM 8/3/2002 +0100, Lewis wrote:
Secondly despite searching various lists i am still unsure of the battery
situation on the OM series using the mercury battery. I bought some
zinc-air replacements (as per a list message i found) and upon testing
the meter readings it seems fine - however further reading leads me to
believe that over time these readings with be incorrect due to the
continual loss of voltage on the battery. I have now read that there is a
converter available (MR-9?) allowing the use of an alkaline battery - is
this the better option?
I've got two MR-9s and they are apparently different, and the manufacturer
has apparently designed them to go with different batteries through the
years. My first one I believe was supposed to go with a SR44/357. The
latest version is designed for the SR43/301. What's the difference? The
battery is rated at the same voltage, but drop off characteristics
differ. How important is it? Don't really know, but the reason I bought
it is to get the best possible replacement for a normal Hg battery, whose
drop off characteristics are what make it ideal for the OM-1, so I'm
taking it seriously.
[snip]
Whatever you decide to use, I'd recommend setting up with it in
conjunction with a professional servicing of the camera. Even though the
MR-9 is supposed to drop in as a replacement for the Hg battery, I have
some doubts. As long as you are getting some service, you could also see
if your technician offers a conversion that allows you to use a simple
SR44/357 cell without requiring the MR-9 at all.
I have two MR-9 adapters in two different cameras (OM-1n and Rollei
35S). The instruction sheet that came with them stated MS-76, a variant of
the SR44, but they work just fine with #357 silver cells and after shooting
many rolls of chromes through them I'm satisfied the metering is
sufficiently accurate.
The web site for the manufacturer ( http://www.criscam.com/ ) now states it
uses the #386 silver cells which are the same diameter but a bit shorter
than the #357 cells.
IMPORTANT NOTES ABOUT SILVER CELLS THAT HAPPEN TO BE THE SAME SIZE:
There is a difference between the specifications for a #301 and a #386, and
between an EPX76 (aka MS76) and a #357:
mAh Volt ANSI # Wt(g) Dia(mm) Ht(mm)
------------------------------------------------
#301: 110 1.55 1132SO 1.7 11.6 4.2
#386: 120 1.55 1133SO 1.7 11.6 4.2
------------------------------------------------
#357: 175 1.55 1131SO 2.3 11.6 5.4
EPX76: 200 1.55 1107SOP 2.27 11.6 5.4
------------------------------------------------
The data sheets also show differences in application and in voltage falloff
over their lifespans.
#301:
Intended for continuous low drain. Data sheet test for voltage falloff is
at 0.103 mA. Voltage drops from 1.5 to 1.3 Volts during last 50f life.
#386:
Intended for continuous low drain with high pulse drain on demand. Data
sheet test for voltage falloff is at 0.238 mA. Voltage drops from 1.5 to
1.3 Volts during last 50f life.
EPX76:
Intended for photo use. Data sheet test for for voltage falloff is at
0.215 mA. Voltage falls from 1.5 V to about 0.9 V during last 600f life.
#357:
Intended for continuous low drain with high pulse drain on demand. Data
sheet test for voltage falloff is at 0.238 mA. Voltage drops from 1.5 to
1.3 Volts during last 100f life.
My conclusions:
(a) For the older MR-9's for which C.R.I.S. stated they used the larger
MS76 cells, it is *much* better to use #357 cells in them instead due to
the voltage falloff curves!
(b) For the newer MR-9's that C.R.I.S. states should use the #386 cells,
these are a better choice than using #301 cells. The #386 cells will last
a bit longer and tolerate higher drain.
-- John
P.S.
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