The Pentax Spotmatic was a classic film camera, first produced by Asahi in 1964. It was a completely mechanical camera, apart from the battery powered Through The Lens (TTL) light meter. Like so many cameras of this era, the metering circuits were powered by now defunct mercury batteries; a PX400 mercury cell in the case of my Pentax Spotmatic SP500. This is what mine looks like:

Pentax Spotmatic SP500 film camera
Pentax Spotmatic SP500 film camera

My particular Spotmatic was rebadged and distributed in the US by the Honeywell company. Like all of the old Pentax cameras, it features an M42 screw mount, which means that a huge variety of lenses can be used. I’ve mounted a Soligor 2.8 24mm lens on mine. You can see how big and heavy it is, adding further weight to the robust metal heft of the Pentax body.

Like my Praktica MTL5B (another favourite), the light meter in the Pentax Spotmatic is of the analog needle match type, and is activated by pushing up a large button near the lens barrel. This button can be left in the activated position until such time as the shutter button is pressed, meaning that stop down metering can take place until one is ready to make a photo. It’s a simple but effective system. When the needle match meter is combined with a lens that has a stepless aperture ring, you can precisely dial in as much over or under exposure as you like to suit the scene and circumstances.

So, how do you replace that old mercury PX400 battery that is no longer produced? Which battery can you use in your newly acquired Spotmatic? The PX400 was a 1.35 volt battery, but luckily for us the Pentax Spotmatic has a bridge circuit, which means that you can put in a modern 1.5 volt battery and the metering circuit will ignore the voltage and still operate normally. It’s a great feature not found on many cameras of this era.

I use the cheap and widely available Energizer 392 Silver Oxide 1.5 volt battery. The Silver Oxide batteries are better in a camera like this because the discharge curve is much more even. The tiny Energizer will fit quite snugly into the battery compartment of the Spotmatic if you also pop in a few cheap rubber O-rings. I bought my O-rings in the automotive section of a local Cheap as Chips store.

This is what my Pentax Spotmatic looks like with O-rings fitted:

Pentax Spotmatic SP500 - battery replacement
Pentax Spotmatic SP500 – battery replacement

You’ll note that I’ve placed a smaller ring around the base of the metal contact, and a larger one just below the screw thread for the battery compartment lid. This arrangement keeps the tiny Energizer 392 battery in place and centred on the metal contact.

Now I just have to load it with some film and get out into the world !

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Pentax Spotmatic – what type of battery to use?
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6 thoughts on “Pentax Spotmatic – what type of battery to use?

  • July 11, 2017 at 9:30 am
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    So the battery doesn’t work without the rubber ring?

    Reply
    • July 11, 2017 at 11:46 am
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      It will work, but the rings are there to make sure the battery doesn’t lose contact with the metal contact. The problem is that the new batteries are smaller than the original Spotmatic battery compartment. The rubber O-rings just ensure a tighter fit. You could also re-purpose some regular rubber bands if need be.

      Reply
  • December 22, 2015 at 11:22 am
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    I’ve got two Spotmatic bodies but seldom shoot them, in part because of the wonky battery situation. I bought a 392 cell as well, and off eBay I bought a custom-made adapter ring. I still have that battery and the ring, but I’m betting the battery is dead by now. For the couple times a year I’d use it, it’s not worth keeping fresh 392s around. It’s kind of a shame. If other cameras used 392s, I’d probably always have fresh ones around and I’d use the Spotmatic more often!

    Reply
    • December 26, 2015 at 3:51 am
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      That’s fair enough. The 392 I bought is silver oxide, but not sure on how long it will last. I’d best go out and use it soonish !! Luckily the batery only cost me a few bucks from the local chemist. That aside, it’s a very nice camera with all you need to get into film. Thanks Jim 🙂

      Reply
    • June 23, 2017 at 6:16 am
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      Use.. ‘Sunny 16’, and just shoot. Who needs a meter.

      Reply
      • July 11, 2017 at 11:48 am
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        Well, yes indeed! I often do use Sunny 16. I just like this camera and sometimes it’s a nice change of pace to use the inbuilt meter.

        Reply

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