Is Panasonic 12-35mm II parfocal?

kolyy wrote:

I am pretty sure you are wrong. The lenses of course have advanced processing engines and the body is not providing current, but voltage. I am pretty certain that the body is only sending higher level commands to the lens when performing autofocus and it does nothing when you put it to manual focus. Adjustment of the focusing motors when zooming has to be done at the level of lens firmware, I think.

Technically I can't be wrong. Or right, since I don't really know; just making educated guesses trying to figure it out. On a more serious note, yea, I see your point, it's a possibility but without any actual understanding of the system, about as likely as my hypothesis. Which I think makes a bit more sense, but who knows.

And of course, correcting for parfocality by adjusting focus is not the same as true parfocality. None of the lenses I have is able to hold the plane of focus very precisely. In particular, you have to fix the focus when zoomed in, otherwise it does not work. If you fix the focus when zoomed out and you zoom in, you end up with a blurred image. That is true with all the lenses I have. Some lenses do not try to hold the plane of focus in the whole zoom range, like e.g. the 12-35/2.8 I mentioned, which simply gives up in the wide end. Also, the work of the focusing mechanism can be quite easily seen in many lenses, as the plane of focus repeatedly drifts and then corrects when zooming.

Maintaining focus when zooming out and not when zooming in is usually an illusion due to DoF differences. Things that seem in focus when on the wide end might actually be wildly out of focus when zoomed in even on a parfocal lens. That's not an indication of anything.