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GH2 Focus Plane Shift While Zooming in 24P

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WillGarr

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I've discovered something disturbing about the GH2. When zooming in 24p the focus plane shifts. This does not happen when shooting 60i.

At first I thought this was caused by the slow shutter speed and slower frame rate creating the appearance of focus loss and assumed it was motion blur. But looking at my footage it is clear that the plane of focus shifts towards infinity and then towards the camera. Within 1/4 second focus is restored.

Has anyone else experienced this?

This makes it impossible to shoot with 24P and the 14-140 lens.

I can post examples if anyone is interested.
 
What lens?

Edit - never mind - shouldn't read this forum when tired...
 
Focus shifting while zooming is not uncommon.
--

The greatest of mankind's criminals are those who delude themselves into thinking they have done 'the right thing.'
  • Rayna Butler
 
Is the 14-140 parfocal? If it's a varifocal lens then you will get a focus shift while zooming. Sometimes even parfocals may not be 100% spot-on at all focal lengths.

Also, did you test this on a tripod on a static scene, to eliminate the possibility of a slight shift in FOV causing the camera to refocus?
 
When zooming, many of the Panasonic lenses will lose focus temporarily. Especially when zooming fast. I never noticed any difference between 24p and 50i/60i, though.

Of course, as has been said, zooming while video recording is usually best avoided, anyway.
 
I guess I'm accustomed to pro film and video lenses that do maintain focus while zooming. Cheap camcorder lenses seem to do this as well.

It seems that during zoom the lens is electronically shifting elements using servos. Traditional lenses use gears to move elements as you physically turn the zoom lever. The servos seem to take some time to catch up. Here's a summary of what I've observed:

Focus plane shift occurs in 24P and 60i.
Focus plane shift is MUCH more pronounced in 24p - don't know why.
IRIS shift also occurs during zooming when in manual iris.

This is a serious limitation of the 14-140 lens/GH2. When users post that one could simply not zoom - well, that's just silly. Zooming is over used but it is one tool that a filmmaker can and should use. Looks like I'll have to go back to my Sony HDV.

Has anyone experienced this with the stock lens?

Do Olympus lenses have the same problem? Would I be better off with the Olympus 14-150?

I'll post some samples soon.
 
Here's some low-rez youtube video that illustrates the problem.

http://www.youtube.com/watch?v=bJf3IzIytlE

Focus shifting and iris shifting are visible at all iris and shutter speeds. Obviously, the larger the iris the more pronounced. This test was shot using the digital extender and f5.6 making focus very critical and thus showing the lens at its worst.

I shot documentary style and I need to be able to re-compose shots while filming. Zooming is an essential tool. If you're shooting music videos it might not be a problem.

Are there better lenses for the GH2? Does this problem also happen on the stock lens?
 
Perhaps a crazy question...does this do it when you are in MF? if not, then it is not the lens and it might be the sudden change in image confusing the contrast detect in the GH2, causing a re-focus.

That may not solve your problem but might give you a work around and something for the Panasonic guys to work on...
 
Mike,

This is manual focus and manual iris. In theory, all auto functions should be off, but I've discovered that that's not how this lens works. During the zoom the servos are moving lens elements to maintain distances and ratios. It is all very clever. Unfortunately, the servos are not quick enough.

Panasonic are telling me to send the camera for repairs. I'm not sure there is anything wrong with it other than design problems. Sending the camera off for repair won't solve that.

Can anyone else reproduce this problem? I'd love to hear from you if you've seen this.

One thing I can't figure out is why it is worse at 24P.
 
If you lock the focus, it is less of an issue. You should really almost never zoom when shooting video anyway.

When you watch professional videos they rarely zoom and when they do it is very slow. Same with panning. Only very slow pans.

I found with my GH2 that I use MF most of the time now when shooting video too.
 
The 14-140mm lens was never said to be Parfocal so i don't get what you are complaining about. Maybe you never shot photos before but just about all photo lenses are NOT Parfocal . This lens is Video Optimized but it was never said to be a Parfocal lens thus you simply can not expect that functionality as it is not a common one for photo lenses and photo cameras. I get its a hybrid and yes i as well am used to shooting Parfocal zoom lenses since i came from film and video cameras like my hpx dvx 16mm film camers. However i never would have expected a Parfocal lens to be default on this camera or let alone as cheap as 500$ for a quality lens like that. Do some research before you buy something? I find it frustrating when i hear, i'm going back to my old camera, the gh2 is still the best video dslr right now, you are going back to something else blaming it on the camera rather than your own ignorance. Shoot prime once in while, you're interested in video right?
 
"Do Olympus lenses have the same problem? Would I be better off with the Olympus 14-150?"

Firstly, It is not a defect or a problem. Secondly this lens is as well is not Parfocal, its designed like 99% of all the photo lenses out there, Varifocal. Sorry.
 
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