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:
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:
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 !