Is there life after aperture block failure?

Massao 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.

Exactly! Applying EV correction negates the claim that Pentax DSLR's work with full functionality with older manual lenses. I don't know how a camera with faulty ABF behaves, but my K-30 with K-50's firmware on it does not require any Abara-kadabralike painting the rear metal elements black, or fiddling with EV compensation

Pentax makes no such claim - you can't use any legacy lens which has an aperture ring and no "A" setting exactly as you would with a modern lens.  You won't be able to use P, TAv, etc. modes at all, for example.  Even in "M" mode, you have to use the green button and end up getting a sort of aperture-priority mode.

What I am saying is that, with the K-50, you can use Av mode, as long as you fool the camera into getting the exposure correct by using the exposure compensation function.

I never said anything about painting the "rear element" black!  That was a reference to the fact that most (all?) M42 lenses have non-conductive rears.  Whereas most K-mount lenses have bare aluminium conductive rears.  And the discussion about Av mode above requires lenses with conductive rears.

If you don't want to bother with Av mode and exposure compensation, then stick to "M" mode and the green button.  But you'll probably get inconsistent exposures, with no two lenses behaving identically with a variety of apertures.

Note: my suggested use of Av mode may well not work with other Pentax models, but it does with the K-50 (at least it does with mine).