Is Panasonic 12-35mm II parfocal?

Stejo wrote:

hindesite wrote:

Why?

Doesn't the example show the possibility (which is my assumption) that the lens manages it own corrections of focus to maintain parfocality; after all, these lens know their own characteristics and could adjust accordingly (just as they used to do using mechanical designs in the past).

Nothing to do with the camera body for this function; AF is not involved.

The lens can't power its AF motor by itself. Nor does it have an advanced processing engine on board typically. In order to keep shifting the elements around to maintain parfocality, somebody has to apply precise amounts of electrical current at specific moments. It seems unlikely that a lens would be allowed access to power on demand without the body provisioning for it.

Furthermore, the more likely scenario is that the amount of current required has to be judged on the basis of the projected image rather than focal length change. Seems reasonable to assume that as you're zooming in and out the body adjusts focus accordingly to maintain maximum contrast at the original focus plane.

After all, if manufacturing tolerances were so precise that all copies of the same model lens have the exact same focus drift when zooming in and out that the same preset amount of power could fix it, they might as well be truly parfocal in the first place.

But this is all conjecture. If somebody knows what's the actual inner workings of the system, I'm all ears. And the speed at which the adjustment happens also had me wondering if it's a DFD thing. Not sure if it's full on CDAF happening at that moment, fast as it might be. If Oly bodies do it too, then it's obviously not DFD. Might be the lens by itself too, as you say. Really don't know.

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.

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.