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01-19-2016, 07:15 AM   #1
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automatic diaphragm

Hi, I recently got pentax 67ii body and while reading on the lenses, I came across the term automatic diaphragm.
I was wondering what this means in terms of what is automatic about the diaphragm

01-19-2016, 07:50 AM   #2
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It means that the camera automatically stops the lens down to the aperture setting selected on the aperture ring when you press the shutter button.

On earlier bodies, you would have to stop down to shoot/meter after composing, then open the aperture back up afterwards to brighten the viewfinder.

Adam
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01-19-2016, 08:58 AM - 1 Like   #3
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+1 to Adam's reply.

If there's one thing consistent in photography is the term "automatic".

I have here on the desk an Asahi Pentax S2, with its 55mm "Auto Takumar". Today's photographer sees nothing automatic about this camera at all. It didn't even have a light meter. But no doubt many a great frame was ruined by forgetting to stop down a pre-set lens to its taking aperture before tripping the shutter. Having a lens that snapped that aperture down as the mirror went up was considered "automatic" at the time.

Later we saw SLRs with automatic exposure, either controlling the aperture automatically with the light, or the shutter speed. These were later dubbed "semi-automatic" cameras when fully programmed exposure SLRs arrived on the scene. Today, all these are often called manual cameras, because they don't have autofocus.

I can only speculate, but I can think that in the future, today's cameras will be dubbed "manual" because they don't fly along beside us and record everything we see
01-19-2016, 12:07 PM   #4
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The Auto function on the lens is mechanical as Adam has said but it also has a metering function. When using a metered body (AE or TTL prism) the Auto function allows wide open metering, even though you may have no intention of shooting wide open. This is due to the connection between the meter and the aperture ring.

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