GH5 Panasonic Lumix GH5 Focus Changing Issue on a rack focus

[tokun1]

Hello Group,

I'm coming from a camcorder background for many years, I just recently purchased my first DSLR (Lumix gh5) 2 weeks ago. The focusing has me completely stumped. I'm using the Panasonic Leica 12-60mm lens, I have the camera on Manual everything, I use the focus ring to focus in on an object to do a rack focus of an object in the foreground, and for some reason the focus keeps changing on me slightly as I pull from one object to another. I have to pull a little bit farther, or less of a pull. This is baffling!..., the camera is locked down, the lens is locked in and set to manual and the stabilizer is turned "off", the aperture, frame rate, and Iso is set, nothing is moving, the tripod is locked down tight. At first I thought is was the follow focus ring, that is was slipping, when I removed the follow focus ring, same issue.

I would greatly appreciate some help as to why this is going on or what I'm doing incorrectly. I'm missing my camcorder about now with my fixed lens.

Thank you!

-Tony

 

[Raz B]

Hello Tony,

Lenses like the Pana-Leica 12-60mm don't have mechanical focusing which directly moves the glass elements to change focus (like with manual lenses).
These electronic lenses "focus-by-wire". Therefore the rotation of the focus rings doesn't affect focus directly, but it sends signals to change focus according the position of the ring as well as the speed of rotation.
For that reason you will not necessarily get the exact same focus points you have marked when you are racking "manually" on those lenses.

Personally I hate focus-by-wire lenses for video work. Nevertheless I heard other systems' wire-focusing, like Sony's, can be even worse than Panasonic's (never worked with a native Sony e-mount lens, so I can't tell from my own experience).

Now here is a bit of good news for you. On the GH5 Panasonic came out with focus racking function which is called "Focus Transition".
It allows you to set up to 3 positions, the focus change speed and then you can move across these points while filming.
Here is a demonstration video of that function:
https://www.youtube.com/watch?v=QeLhpUCvxgw

I hope this was helpful!

Best Regards,
Raz.