Manual Aperture

I want to use my Pentax A in manual aperture mode but when I put it on the camera it straight away opens the aperture fully and I cant close it. The lens is not on "A" setting and Manual Aperture setting is on in the menu. What am I doing wrong?

Is that not correct. does the iris not close to the set aperture only when the shutter is operated?

When it is off the camera and I turn the aperture ring it closes down fine but as soon as I put it on the camera and twist the aperture opens fully

That is how all K mount lenses work.

The camera would be unusable if it didn't open the aperture fully for looking through the camera. It would be very dark!

The aperture only closes down momentarily when taking a photo or when you use the optical DoF preview function. Look into the camera when taking a photo and you will see.

The aperture ring on an A lens is useless as you can manually control the aperture from the control wheels on the camera. In fact, it is better to do it that way because the camera records the lens data, otherwise it records nothing.

With M and K lenses you need to use the green button for stop down metering.

Surely if the lens is not set to A then I have full control of the size of the aperture via the ring?

It seems you misunderstand how the aperture ring operates and how the aperture is actuated by the camera.

The aperture ring mechanically sets the minimum that the camera's aperture actuation lever can close the aperture. This only happens when the shutter is pressed and an exposure is made. Using the aperture ring does not bypass this mechanism as it it the way the k mount has always operated.

The A setting just allows the camera to read the maximum and minimum aperture a lens has available and thus control the aperture from the body. The camera will know how far to move the aperture lever and it will not need the mechanical stop provided by the aperture ring.

By default the aperture of a k lens is fully closed and on the camera it will be fully open.

You still get manual control with or without using A as long as the camera is set to a mode where aperture can be chosen manually. In fact, you get more settings in camera as you can do 1/3 stops or 1/2 stops. Many K, M and A lenses only have half stops at best and between certain f numbers they have no stops at all!

So set the aperture to A and get a much better experience, flexibility and control.

Thanks Don, however I want the control when I put the lens on tubes and I'm sure I have been able to do this before, I may be mistaken though.
Steve

If the tubes do not have the aperture control pass through lever the lens will work as though it is not fitted to the camera. IOW a very old set of extension tubes.

Greg

The only example I have is the Helicoil link

Greg

It's OK I'll use the reversing ring that will give me what I want... link