I have a new Tamron 1.4x MC4 with 6 contacts TC, and it works fine in AF. However, with some of my AF lenses and the camera set to manual focus, the TC does not disengage its AF gear & because of this it is making manual focus a problem. Similar effect to trying to turn a focus ring with the camera's AF turned on. The problem exists with the lens & TC removed from the camera body, and the same problem exists mounted on either my K100Ds or ZX-7. From inspecting the TC, the spring-loaded AF gear creates additional drag and it does not disengage from the lens' AF gear. Doing a quick search, I found a couple other people that have had similar issues -
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/22091-tamron-1...4-telecon.html https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/29913-tamron-t...erter-bad.html
With my Takumar F 70-210mm 4-5.6, there is no real problem, the focus ring moves freely & although the TC gear spins with the focusing of the lens, it's difficult to notice the difference with the added drag of the TC.
With my 18-55mm DA, no problems since the AF gear isn't even engaged when manually focusing this lens.
With my Tamron 70-300mm LD Macro, gears are again engaged and it does add a little bit of drag, enough to be annoying and add noise as you hear the TC gear spinning.
And with my Sigma 28-300mm Macro, manually focusing with TC adds enough drag that it's almost impossible. Apparently because the lens has a very short focus throw, the addition of the TC's drag with the high gear ratio makes turning the focus ring tough and not practical.
This may have been discussed in more detail somewhere, but I read through this thread and didn't notice mention of it. It would seem as though, unless my TC is defective and I don't think it is, that this would be an issue brought up in this thread. The problem seems to be that either the TC gear should retract if the camera is set to MF mode, and/or the TC gear has too much resistance and because of this it creates a lot of additional drag in MF with shorter focus throw lenses.
It may be that this has not been brought up much or even noticed by some that may be using this TC on longer lenses that have relatively long focus throw. But on shorter focus throw lenses like 'Super zooms' of 28-200, 18-200, and some newer AF lenses with very short focus throw, this is an issue. And unless other TCs are designed to retract the focus gear or have very little resistance, I would think that similar problems exist with other TCs than just the Tamron 1.4x.
So, has anyone else with this or other AF TCs noticed added drag issues in manual focus, especially with short focus throw lenses? I don't think anything is wrong with my TC, so I suspect that others will also find some of these issues. For my Sigma lens in particular, the only solution is to press in the TC's lens dismount button while manually focusing, as it retracts the TC gear. Sorry for the long post, just wanted to provide plenty of detail. I've been spoiled by my other AF system with TC's and extension tubes, a Canon system with no mechanical linkages...