On Fri, May 04, 2012 at 12:29:25PM -0600, Tom C wrote: > > Other information as I've experimented. > > If I leave the lens in a non-A setting, and remove it from the camera > and put it back on, operation is fine. > > If I set the lens to the 'A' setting and remount it, the symptoms > recur (darkish viewfinder and inability to focus). At this point if I > go off of 'A' setting to manual aperture, it continues to NOT achieve > focus at every aperture, until I reach the click between f/11 and f/8, > at which times it focuses. It does this fairly consistently. > > If I immediately rotate the aperture ring from the click between f/8 > and f/11, to a smaller aperture, f/22 for instance it again DOES NOT > focus and the viewfinder is darkish. > > If I have the lens in 'A' when I mount it on the camera, immediately > dial down to f/2.8, and then up through all the aperture settings > including 'A' it focuses fine. > > So I'm guessing there is something electro-mechanical in nature going > on with the aperture-ring? > > Also, I've never noticed this before, but when in non-A mode I don't > see an aperture readout in the viewfinder or top-panel. Just --. May > be that's normal and I never saw it before.
That "--" readout is normal. What is slightingly referred to as the "crippled K-mount" on all the DSLRs doesn't have the aperture follower linkage, so there is no way for the body to know what the aperture ring on the lens is set to (other than the separate "A" position detection). It still sounds to me like a purely mechanical problem. Normally, when a lens is off the camera, it will be stopped down to the aperture set on the aperture ring (or f/32 for the "A" position). As you rotate the lens while mounting it on your camera the mechanical aperture linkage between the body and the lens is supposed to engage, and this will open the iris up to maximum aperture. It sounds to me as though this is not happening when you have the lens set to "A". If (after the lens is mounted on the body) you then turn the aperture ring to f/2.8 and back to "A" again this will give the two parts of the mechanical linkage another chance to mate properly. It sounds as though doing this is enough to get your lens working correctly again. Take a look at the aperture linkage on your lens, and compare it to the lever on any other lens. It should stick straight out parallel to the axis of the lens. If the tip of the lever (the part that sticks out the furthest) is bent inwards towards the axis of the lens it's possible that the very slight flex in the lens that you introduce while mounting it causes it to just miss engaging with the body (or, alternatively, it's possible that the lens itself tilts the lever slightly when the aperture ring is all the way round to the "A" position). Turning the lens aperture ring to f/2.8 after the lens is mounted forces the link back to the correct side of the body coupler, whereupon normal operation should resume. If the lens always works normally if you have the aperture set to f/2.8 when you mount it I'd suggest simply doing that, and only turning the aperture ring to "A" after the lens is mounted. Failing that, I'd consider trying to bend that lever very slightly so that the tip of it moved fractionally further away from the axis of the lens, but I'd only do that if the workaround failed. Has the lens ever been dropped, as far as you know? That can bend that lever if you're unlucky enough to have that be the first part of the lens to come into contact with something hard (and that will push the tip of the lever towards the lens axis). -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
