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by evan-pak

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The Pentax K1000 has a meter that is always on. The manual says the only way to keep the meter from draining the battery when not in use is to put a lens cap on it.

However, the needle does not move when the camera's exposure settings would produce an underexposed image. Is it possible that if I set the ISO to 8, the shutter to 1/1000, and the aperture to ƒ/22, I will have effectively turned the meter off?

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up vote 5 down vote accepted

The K1000 needs darkness in order to turn off the meter. Changing the ISO, shutter speed, and aperture will just change what the meter is looking for to balance the needle.

The circuit that controls whether or not the meter gets power is controlled by a light-sensor that watches for light on the focussing screen. If sufficient light is present (EV2 @ ISO100, I think), then the photo cell allows current to flow from the battery to a transistor, which in turn powers up the main metering circuit. In a bright room, enough light can get in through the viewfinder to trigger this.

If no light enters the camera and hits the focussing screen, then the light sensor doesn't allow current to flow, and effectively switches the metering system off.

According to the repair manuals that I've read, it was pretty common back in the day for people to complain about the battery drain, and the recommended fix was to leave the lens cap on, and if possible leave the camera in a case.

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Excellent explanation. Thanks! – keyofnight Feb 27 '15 at 2:51

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