FUJI X-E3 Manual Focus refocus itself when zoom

[Max94545]

Hi there, 

 

I need help to figure out why my Fuji X-E3 on manual focus keep on adjusting its own focus, when I zoomed in or out on the lens. I am using the movie preset as it is being use for streaming. 

I have multiple units and it does the same thing. Any inside you have ? Fuji tech support stating that it should not be doing that as it is set at Manual Focus. 

Let me know if you have a pointer. 

Thank you, 

Max

[mawz]

Most likely you've simply run into the fact that very few zoom lenses are parfocal.

In other words, when you zoom, the focus point shifts naturally and must be compensated for by the AF system or the user.

[Max94545]

What is that mean ? Do you think that It's a design flaw ? Coz when doing video live zooming, that movement somewhat attracting the eye to find out what's going on. 

 

[mawz]

On 7/24/2020 at 8:17 PM, Max94545 said:

What is that mean ? Do you think that It's a design flaw ? Coz when doing video live zooming, that movement somewhat attracting the eye to find out what's going on. 

 

It's extremely difficult to design a zoom that holds consistent focus when zooming (in fact Internal focus lenses are nothing more than zooms designed to exaggerate this characteristic, which is why they focus breathe, that's just a side effect abusing zoom to focus). That's one reason why real cine zooms are large and expensive, they're also parfocal.

Since stills work is not affected by how parfocal the zoom is, it's extremely common for lenses designed for stills mounts to do this. It is a problem for video and we're starting to see lenses which actually compensate for this electronically, but none of the Fuji lenses do this.