1

In A mode, the Canonet GIII prevents the shutter from being released unless the metering is within a certain range (i.e. the available range of apertures it can set).

How does it do that? And how does it set - as in, physically control - the movement of the iris blades?

There has to be some sort of transducer in each case that transforms an electronic condition into a physical one. I think it must be a lever coupled to the movement of the light meter needle, but I can't remember and I'd have to take one apart to verify this; perhaps someone else can confirm.

Daniele Procida
  • 977
  • 7
  • 19
  • If it is like the Olympus 35RC, the aperture on the lens goes from narrow to wide ("stops up") as the shutter button is pressed. The needle for the light meter rheostat blocks the "stop up" at the appropriate aperture. If the needle does not engage the aperture, then it travels past aperture control and blocks the shutter from firing. Of course the Olympus 35RC only has shutter priority, so the Canonet might be more complex. – Bob Macaroni McStevens Mar 19 '21 at 03:31

1 Answers1

1

One common mechanism used in early automatic exposure camera uses a clamping bar that, at the start of the exposure, keeps a meter needle fixed at its most recent position. Once this has happened, a spring loaded mechanism pushes the lever controlling aperture, shutter, or both (via a mechanical curve) towards one extreme setting. This mechanism is laid out so that its travel is limited by the clamped down meter needle.

If internet sources can be trusted, the "Canonet QL17 GIII" does use a "trapped needle" system, which is exactly what I described here.

rackandboneman
  • 7,212
  • 19
  • 32