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11-01-2009, 01:03 PM   #1
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Yes! My Spotmatic F will take a LR44/357 silver oxide battery

Kinda got to this discovery sideways and am pretty happy about it because my later K-mount cameras (ME Super, Super Program, P30t and Ricoh KR/XR models) all take a LR44/76s/357 type silver oxide battery that are still abundant and inexpensive. I had tried a 675 zinc-air hearing aid battery with an O-ring around it. I was using that substitute because the 675 version is almost as thick as a 625 alkaline, just needed an O-ring to fill out the diameter. However, I stumbled on the fact that the SR44 batteries are the same size as a 675 battery (found on Photoethnography web site).

So, I upended my Spottie, fished out the O-ringed 1.4 volt hearing aid battery and swapped it for a 1.5 volt 357 battery I got at Lowes, put the O-ringed 357 in the camera and tried it on my standard lamp-shade light source. Same meter reading. So, I'm down to 2 types of batteries, the 357/LR44 and the 394 silver oxide that I use in my Type 1 black Spotmatic. Both of these types are 1.5 volt versus the 1.35 that the SP and SPF Spotmatics originally used but the various types of bridge circuits in these cameras will handle the higher voltage.

11-01-2009, 01:05 PM   #2
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QuoteOriginally posted by Tom in Delaware Quote
Kinda got to this discovery sideways and am pretty happy about it because my later K-mount cameras (ME Super, Super Program, P30t and Ricoh KR/XR models) all take a LR44/76s/357 type silver oxide battery that are still abundant and inexpensive. I had tried a 675 zinc-air hearing aid battery with an O-ring around it. I was using that substitute because the 675 version is almost as thick as a 625 alkaline, just needed an O-ring to fill out the diameter. However, I stumbled on the fact that the SR44 batteries are the same size as a 675 battery (found on Photoethnography web site).

So, I upended my Spottie, fished out the O-ringed 1.4 volt hearing aid battery and swapped it for a 1.5 volt 357 battery I got at Lowes, put the O-ringed 357 in the camera and tried it on my standard lamp-shade light source. Same meter reading. So, I'm down to 2 types of batteries, the 357/LR44 and the 394 silver oxide that I use in my Type 1 black Spotmatic. Both of these types are 1.5 volt versus the 1.35 that the SP and SPF Spotmatics originally used but the various types of bridge circuits in these cameras will handle the higher voltage.
Oops! I'm actually using a SR44 type battery, the LR44 is an alkaline, the 357/SR44 is a silver oxide.
11-02-2009, 01:00 AM   #3
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Aye, the Spotties are remarkably prescient in that respect.

Most of the mercury-celled cameras use the voltage from the batteries as the baseline voltage for the meter, and if the battery was of a different voltage to the one it was designed for, then your metering would be off. Spotties had buffer circuitry in there, I think. A bit more complex, but a bit more robust, future-proof, and you don't have to worry about the battery's output curves, either - which is in fact one of the advantages of those mercury batteries.
11-02-2009, 05:16 AM   #4
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According to Camerapedia, there are no Pentax cameras that require mercury cells or special replacements. All Spotmatics have voltage regulation circuitry and will work fine with alkalines.

04-30-2010, 09:04 AM   #5
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QuoteOriginally posted by Erik Quote
According to Camerapedia, there are no Pentax cameras that require mercury cells or special replacements. All Spotmatics have voltage regulation circuitry and will work fine with alkalines.
Or the best bet - Silver Oxides

Alkaline batteries have a poor power drop-off curve and the meter will start to read wrongly long before the battery is flat.
04-30-2010, 11:53 AM   #6
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QuoteOriginally posted by SpottyMatic Quote
Alkaline batteries have a poor power drop-off curve...
Yes...

QuoteOriginally posted by SpottyMatic Quote
... and the meter will start to read wrongly long before the battery is flat.
... and no, or at least not as regards a Spotmatic F (or K1000 or KM). A "balanced bridge" meter circuit is not voltage sensitive with regard to its center point. As a battery ages and weakens, the amount of deflection when the meter is off center may vary somewhat, but center stays center.

Whether the non-F spotties use a bridge circuit is in some doubt depending where you read. My SPII's meter hangs below center when switched off, which I find slightly suspicious. But I'm using alkaline in it anyway, and it has done well so far.
04-30-2010, 05:53 PM   #7
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I read somewhere online that the later SPs and SP-IIs were built so that the meter would indicate just below centered when off so people wouldn't think the meter was on when it was actually off. It's kind of unsettling when you first see it though, I agree (and made me call into question the accuracy of my SP's meter at first, which is the same way.)
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