Is there life after aperture block failure?

flektogon wrote:

Futax wrote:

flektogon wrote:

Futax wrote:

No, it won't stop down correctly if you set it to "A" (which is the equivalent to F22 or whatever as far as your camera is concerned). That would be just the same as using a lens without an aperture ring. Just set the aperture ring to your chosen aperture (which might well be an aperture which maximises sharpness), and in Av mode it will stop down to that aperture (at least with my K-50 it will).

Since the exposure metering is done just before you take the shot, and the camera assumes the aperture is wide open (it knows no different, as the aperture ring doesn't communicate back to the camera), the camera will overexpose unless the aperture is actually set to be wide open.

So you have to use exposure compensation to counteract this. For example, if it's an F4 lens and you set the aperture ring to F8, you will need +2EV compensation.

Give it a try, and report back, because that is how my own K-50 behaves, and I'm assuming it applies to all K-50s. It'll hopefully be of help to a lot of people!:-)

I am a little bit confused as why the EV correction has to be applied. So the first thing first. As I understand, camera with the failed aperture solenoid can't control position of the aperture lever, so when you fully press the shutter button, it will move the aperture lever from fully open to fully closed. This is what happen when the lens doesn't have the aperture ring, or the Pentax-A lens has the ring in the "A" position.

Now, on a Pentax-A lens I will set the aperture ring to f:8.0 and I set the camera to the AV mode and set there f:8.0 as well. If a camera suffers from that faulty solenoid, will it be still able to close the lens to the preset position?

The camera knows it isn't capable of setting aperture, so ignore the thumbwheel - it won't do anything. But yes, the camera will still operate the aperture stop-down mechanism, so the lens will stop down to f8 when you take the shot because that's what you set the aperture ring to. But the camera is assuming the lens is wide open, as far as exposure is concerned.

Why? Yes, camera uses fully open lens (its brightnes has to "sense" from the lens aperture lever position, and regardless whether its aperture control solenoid works properly or not. Then it determines correct exposure parameters. However, if in the Av mode you set (by the wheel) different than fully open aperture value, camera will immediately apply needed EV correction to its initially measured value. Actually, it is NOT the EV correction what camera will make! It is just the aperture/shutter speed shift what camera applies.

If yes, then why to apply any EV correction? The camera will make the exposure measurement with the half pressed shutter button and at that time the lens is fully open. The camera somehow has to detect what is that fully open aperture (like f:4.0) to make a correct exposure calculations. And it knows that the actual aperture will be f:8.0 (and you have the aperture ring at the f:8.0 position already set), so camera will make that needed EV correction itself. Actually there shouldn't be any difference between in the camera/lens behaviour with a faulty and normally working aperture solenoid. Or am I wrong?

No it doesn't - that's the point. Once you move away from the "A" position, the camera has no knowledge of what you set the aperture to. The only way of getting correct exposure is to use exposure compensation.

The camera is unable to control the aperture lever on an affected K-50, other than to either a) not operate it at all or b) operate it fully. It can't stop it halfway at f8 like it should in a "good" K-50 - that's the whole problem.

When you fully press the shutter button, properly working camera will set (by precise shifting the aperture lever) the required aperture as you have selected on the camera. This happens to the modern lenses without aperture ring, or an A lens with the aperture ring set in the "A" position.

If you use M lens, or A lens with the aperture ring set to some specific value (for example f:8) the lens still remains fully open, so camera can measure correct exposure the same way. If you fully press the shutter button, it will move the aperture lever to the right position. However, camera with a faulty solenoid is not able to position the lever precisely, it will push it fully to the limit. If the lens was in the "A" position (or for any ring-less lens) this would mean to set the minimum aperture (like f:22) and a gross underexposure. But with the manually preset aperture value on the lens everything should work properly.

Below applies to lenses which are either K-mount or KA-mount and later which have a not been set to A mode (or have no aperture ring).

Just accept what I'm saying: with the K-50 and a legacy K-mount lens, in Av mode the camera will operate the aperture lever.  Unlike most other Pentax cameras, which will NOT operate the aperture lever.  With those cameras, if you try Av mode, all shots will be taken with a fully open aperture.  Regardless of where you set the aperture ring.

You can use this to your advantage if you have a K-50 with aperture block failure.  Since the camera operates the lens's aperture mechanism, all it has to do is provide the correct exposure.  The camera has no knowledge of the set aperture (it has no way of knowing that), so you have to use exposure compensation.

Maybe Pentax views this as a bug with the K-50 firmware - I don't know.  Doesn't matter, I hope they haven't "fixed" it with a firmware update (I'll give you my camera's firmware details in due course).

Also, this may apply to cameras other than the K-50 (for example, K-30, K-500 etc. - I don't know - I hope so).