Panasonic G Vario 100-300 (H-FS100300) lens don't kept infinity focus when shooting videos

FlightVideo wrote:

Dear all,

Last weekend I used my new Panasonic G Vario 100-300 (H-FS100300) lens to shoot videos. I bought it to use with a GH4 to shooting ultra HD videos of aircraft in flight and publish them on my Youtube channel.

I set the focus on MF (Manual) on the GH4, I move the focus ring on the lens to infinity so I expected that this set was kept during video shooting as did my 13 years old canon lens. I noticed that when zooming the lens losts the focus and the final videos was orrible. I tryed to shoot videos by keeping the zoom fix or by zooming slowly to give to the lens the time to refocus but the final result was poor.

Can you suggest me a solution? I don't need a dynamic focus, keeping infinity focus as old lens did is enought for me.

I shoot some videos with an Olympus 75-300 lens also with the GH4 and this lens was able to kept the focus on infinity and the final videos was very good.

Thanks in advance.

Ruggero

Panasonic lenses has "fly by wire" focus. Focus ring has no infinity point. Also the focus aid meter in screen has no absolute points, it is just "about" aid. The 100-300mm lens is not parfocal so focus shifts when you zoom.

If you want fixed focus you can not zoom or shut the camera. I cant remember if the focus is lost also when camera is going to sleep mode. So focus carefully and dont zoom or shut off.

The lens may maintain focus during zooming if first focus in 300mm and then using as small aperture as possible. I think that when zooming many times back and forth the focus is slowly lost.

Vesku wrote:

FlightVideo wrote:

Dear all,

Last weekend I used my new Panasonic G Vario 100-300 (H-FS100300) lens to shoot videos. I bought it to use with a GH4 to shooting ultra HD videos of aircraft in flight and publish them on my Youtube channel.

I set the focus on MF (Manual) on the GH4, I move the focus ring on the lens to infinity so I expected that this set was kept during video shooting as did my 13 years old canon lens. I noticed that when zooming the lens losts the focus and the final videos was orrible. I tryed to shoot videos by keeping the zoom fix or by zooming slowly to give to the lens the time to refocus but the final result was poor.

Can you suggest me a solution? I don't need a dynamic focus, keeping infinity focus as old lens did is enought for me.

I shoot some videos with an Olympus 75-300 lens also with the GH4 and this lens was able to kept the focus on infinity and the final videos was very good.

Thanks in advance.

Ruggero

Panasonic lenses has "fly by wire" focus. Focus ring has no infinity point. Also the focus aid meter in screen has no absolute points, it is just "about" aid. The 100-300mm lens is not parfocal so focus shifts when you zoom.

If you want fixed focus you can not zoom or shut the camera. I cant remember if the focus is lost also when camera is going to sleep mode. So focus carefully and dont zoom or shut off.

The lens may maintain focus during zooming if first focus in 300mm and then using as small aperture as possible. I think that when zooming many times back and forth the focus is slowly lost.

I don't think that the problem worsens with zooming back and forth, the problem is the lens is not parfocal. That means the lens focuses to a different distance as the focal length changes - if set to focus at infinity at 300mm, while it may change focus at shorter lengths, it will return to focus at 300.

It makes the 100-300 very restricted to use for video. In some ways it may be better to use a prime telephoto.

I wonder how many other m4/3 lenses are not parfocal? I don't recall it ever being made clear in any specs.

This is a compromise made at the design stage, the underlying assumption is that with modern cameras with AF, there is no cost to refocusing at each shot, which unfortunately doesn't apply to video. In film days, it was virtually a given that with decent lenses you could zoom in, focus and be fairly sure that focus was reasonably maintained over the whole zoom range - in fact, this was the only focus "aid" we had, apart from split and microprisms in the viewfinder.

It is well worth considering older legacy lenses for video - the quality can be pretty good, MF is a given (though you will still need to search for infinity) and zooms are more likely to be parfocal.

Thank for the suggestion on hot to focus. It's very useful for mbe becouse I usually shoot for 5 10 minutes then I have time to re-focus.

The strange is that with the Olympus lens I didn't experienced this issue, it worked fine.

I also updated the firmware to version 2.0 that has update on focusing with videos and maybe this can be the cause.