Is Panasonic 12-35mm II parfocal?

kolyy wrote:

Sean Nelson wrote:

kolyy wrote:

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.

That's true of parfocal lenses as well. You simply can't see enough detail when zoomed out to be sure that the lens is properly focused when zoomed in. It's always been the case for all lenses that you zoom in and focus first if you want to maintain focus across the zoom range.

Ok, I don't have any truly parfocal lens, but I think the plane of focus should not shift at all, right? So if I can focus correctly with peak sharpness on my subject, then I should be able to zoom in.

I don't have a 12-35 so I can't comment on how it performs.   But even with a truly parfocal 3X zoom the image is magnified 3X at the long end compared to the wide end.   No matter how carefully you try to focus at the wide end, even if you use magnified view, when you zoom in the objects in the image are going to be 3X larger.   If you then use magnified view on the zoomed-in image you're almost certainly going to discover that you didn't focus exactly correctly.  That's why you zoom in to focus first, and then zoom out to do whatever it is you were planning to do.

With a parfocal lens (or even a "simulated" parfocal lens) you don't zoom in to focus because the focal plane shifts, you do it so that you can focus as accurately as possible using the maximum possible image magnification.

It's no different than the reason you use magnified view to focus a prime lens.   The more magnification you have, the more accurately you can focus.