GH2 Focus Plane Shift While Zooming makes the 14-140 useless

W

willgarr

New member
Great camera, zoom lens is useless! That's my verdict after trying to use the GH2 with the 14-140 lens for documentary and event video. Here's what I've observed:

with the camera set to manual everything, focus plane and iris shift while zooming. This is most noticeable in 24P and less so in 60i.

Please let me know if you have experienced this. I need to determine if there is a problem with my camera/lens or whether it is an endemic design flaw. Here is what I've learned thus far:

The panasonic lens does not maintain focus and iris as you zoom - it uses servos to adjust focus and iris to create an effect similar to the varifocal lenses used on high end film and video cameras. These servos take some time to make the adjustment and therefore while zooming a shift in focus plane is clearly visible.

Here's some test footage showing the effect. This was shot to maximize the effect using the digital extender and a large iris. http://youtu.be/bJf3IzIytlE

Please don't tell me not to zoom. Zoom is essential for reframing shots in documentary production where action is not controlled.
 
willgarr said:
Great camera, zoom lens is useless! That's my verdict after trying to use the GH2 with the 14-140 lens for documentary and event video. Here's what I've observed:

with the camera set to manual everything, focus plane and iris shift while zooming. This is most noticeable in 24P and less so in 60i.

Please let me know if you have experienced this. I need to determine if there is a problem with my camera/lens or whether it is an endemic design flaw. Here is what I've learned thus far:

The panasonic lens does not maintain focus and iris as you zoom - it uses servos to adjust focus and iris to create an effect similar to the varifocal lenses used on high end film and video cameras. These servos take some time to make the adjustment and therefore while zooming a shift in focus plane is clearly visible.

Here's some test footage showing the effect. This was shot to maximize the effect using the digital extender and a large iris. http://youtu.be/bJf3IzIytlE

Please don't tell me not to zoom. Zoom is essential for reframing shots in documentary production where action is not controlled.
Click to expand...
I have noticed this as well. Very frustrating.
 
willgar,
Thats one of the reasons many of the folk here dont use the 14-140 (not parfocal, aperture changes while zooming). You can add to that the very slow max aperture.

To solve part of this problem, I plan to buy some of the Super High Grade Olympus lenses when I have the funds. These have fixed aperture, and max f2.0. But I am almost sure these are not par focal as well, so not a perfect solution for you (I will happy if proven wrong).

I'm almost sure thats why other folk here use PL lenses on their GH1/2s. Only way you can get fast parfocal zooms is with lenses made for real filmaking, and that costs big bucks.
 
I'm using the Olympus 35-10mm f2.0 and it's a superb lens, but I don't think it would satisfy the OP's complaint. In addition to its remarkable f2.0 performance, the 35-100mm was designed with internal zoom and focusing mechanisms, which grant it a completely fixed front lens barrel that neither extends nor rotates. This keeps the lens' four-pound mass from shifting balance as you zoom and focus it on your tripod.

Like all electronic-focus Olympus and Panasonic lenses, however, the 35-100mm has no built-in mechanism to keep its focus and aperture mechanically constant as the lens is zoomed. It is utterly dependent on the camera to dynamically readjust its internal settings to simulate the properties of a truly parfocal lens. As the OP pointed out, the camera's dynamic control of the lens may lag at times during fast zooms, resulting in visible defocusing during video takes. The lens also breathes while focusing and the exposure may shift slightly with one or more clicks during a zoom, depending on your aperture settings.

In most cases, I use the Olympus 35-100mm as a variable prime mounted on a tripod in a fixed location. It's capable of gathering an uncanny amount of light in a dimly lit theatre while allowing near-complete freedom of composition. With familiarity comes a good feel for how far you can zoom without visibly degrading your focus.
 
Yes the 14-140mm f/4 to f.5.6 tells you right there in the name that it has a variable aperture. You could set it at f/5.6 or above when at 14mm and then it will stay fixed. But that's pretty slow.

Panasonic markets this lens as their "movie lens" for the GH2 but it's not a true video lens. Not only is it not a fixed aperture lens and not parfocal, there is another problem with it. When you shoot in shutter priority mode on the GH2 or in Auto Iris mode on the AF100, the lens changes aperture in "steps", and you can see the jump in light levels in the footage. Not only are pro video lenses parfocal, they also have a stepless iris to avoid this. Unfortunately all the Panasonic lenses do this, they are consumer lenses and not professional movie lenses.

The solution I worked out is to get a professional B4 2/3" video lens and a B4 to micro 4/3 adapter. With the builit-in 2x extender, these lenses cover the micro 4/3 sensor with no vignetting. I also put together a cable and battery to power the zoom rocker on the lens. Focus is still manual of course.

You can put together a nice system for well under $1000. The adapter is $320 and the lenses vary in price depending on the age and condition. I worked out a deal with the manufacturer of the adapter and picked up a number of these lenses & I'm putting them together for GH2 and AF100 users. I've sold a few on eBay already. The adapter has a tripod mount on it, and in addition I just got in some rail support systems that will balance the whole setup nicely, although it's not absolutely necessary.

Anyone who's interested can contact me, I'll give dvxuser members a better deal and shot at some of the lenses and accessories to do this. I've shot some footage already & I'm pretty happy with it.

Here is some sample footage: The A camera, stage left, was the GH2 with a14x B4 lens. These are the shots that have zoom. The B camera shot from stage right was a Canon Vixia HD video camera. You can see that the footage shot with the B4 lens works well in low light and has a nice quality to it. This was shot wide open (f/1.7 x 2x = f/3.4) and the lens gets sharper if you stop it down a little.


B4_Adapt004-1.jpg
 
What's funny is how this new DSLR revolution has reduced us to using inferior equipment with compromised workflows. Old broadcast lenses like the one shown above is inexpensive because it wasn't designed to resolve HD. It only had to be manufactured to resolve SD resolution, so chances are it's not going to be nearly as sharp as the 14-140 kit lens. Also, since those lenses were designed for 3 CCD cameras and not CMOS, you're going to get chromatic aberration, especially at wider apertures. Not to mention many of these lenses won't cover the entire GH2 sensor, so you'll get vignetting in the corners on wide-angle shots.
In the case of both the 14-140 kit lens and the 2/3" lens, you need to stop down quite a bit to avoid either roaming aperture or softness. In which case you have deep depth of field but you have to crank up your ISO to compensate for the light loss. Not to mention that you have no powered zoom, so you're automatically tied into a 1970's documentary aesthetic when you manually zoom your lens and try to simultaneously focus.
By contrast, any prosumer camcorder has a built-in powered zoom lens that looks pretty sharp wide open at f1.4 or so. They have an ISO between 400 and 800, and the smaller chip gives you deeper DOF so you aren't hunting for focus every time somebody in the shot moves forwards or backwards a few inches. CCDs instead of CMOS means no rolling shutter problems. No moire and aliasing issues. XLR inputs means no double-system sound or Radio Shack kluges to construct. But these cameras have suddenly become uncool even though they are much better at handling the job of live events or run and gun documentary work.
 
dvbrother said:
But these cameras have suddenly become uncool even though they are much better at handling the job of live events or run and gun documentary work.
Click to expand...

But they're SOOO uncool! ;)

All kidding aside, I'm actually planning on using my GH2 for an outdoor documentary-style shoot simply because I don't have to shlep my larger camera with me on a hike.
I've also managed to get it into places that they wouldn't allow a full sized camera, so there is merit to using them when you can, although you have to put up with an admittedly compromised workflow.

But I'm having second thoughts now because of lens selection- I have a thread in the DSLR general discussion here: http://www.dvxuser.com/V6/showthread.php?271235-Equipment-recommendation-for-outdoor-docu-style

Trying to determine if using the kit 14-45mm lens at F/8 will still noticeably "step" the aperture as I zoom, because I could really use the IS on a shoot like this. I really wish there were a constant aperture zoom with IS for M4/3rds that wasn't as ridiculously expensive as those Olympus ones.
As far as parfocal- is that the same as "internal focus"? Someone recommended I look into a vintage F/3.5 zoom since there are many of them with internal zooms. Obviously, I'd be losing IS so I'll need to be more stable, but will that let me zoom and keep focus? Or does one have nothing to do with the other?

Also, Turbodog, that lens looks really cool mounted on the front of the camera (shows you mean business), but the footage just looks OK. Once you are losing that much light with the extender, one can't help but start to wonder if a vintage manual zoom wouldn't be cheaper and better looking. Man, there is some serious jello/jitter at one point as well!
 
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I've managed some smoothish zooms with the 14-140. We used it as a roving sideline cam on some football games I shot a few months back, and it performed well... of course I'd stopped down to about f8 for depth, so the aperture never stepped, and zooms typically followed action, and I was shooting 720p60 - all of which contribute to hiding jerk zooms.
 
I'm shooting a surfboat marathon right now in Oz... the event is a 7 day slog out.. where they row down the coast line to a new town each day...

I'm using the HPX302 on the beach to keep the client happy (looks like I've got a big camera)... but out at sea it's all GH2 and GoPro's...

The GH2 has been fantastic... using the 10-140 lens... the IS is saving my life as we get bashed around in boats and rubber duckies...

I'm uploading footage to the networks each day from the beach using a broadband card... it's a tricky gig...

I did this event before with a HVX202 and HPX170 and the GH2 is killing it compared to those cameras..

Here's a older clip using the HVX/HPX... http://youtu.be/3MAisxyvbWg
 
dvbrother said:
What's funny is how this new DSLR revolution has reduced us to using inferior equipment with compromised workflows. Old broadcast lenses like the one shown above is inexpensive because it wasn't designed to resolve HD. It only had to be manufactured to resolve SD resolution, so chances are it's not going to be nearly as sharp as the 14-140 kit lens. Also, since those lenses were designed for 3 CCD cameras and not CMOS, you're going to get chromatic aberration, especially at wider apertures. Not to mention many of these lenses won't cover the entire GH2 sensor, so you'll get vignetting in the corners on wide-angle shots.
In the case of both the 14-140 kit lens and the 2/3" lens, you need to stop down quite a bit to avoid either roaming aperture or softness. In which case you have deep depth of field but you have to crank up your ISO to compensate for the light loss. Not to mention that you have no powered zoom, so you're automatically tied into a 1970's documentary aesthetic when you manually zoom your lens and try to simultaneously focus.
By contrast, any prosumer camcorder has a built-in powered zoom lens that looks pretty sharp wide open at f1.4 or so. They have an ISO between 400 and 800, and the smaller chip gives you deeper DOF so you aren't hunting for focus every time somebody in the shot moves forwards or backwards a few inches. CCDs instead of CMOS means no rolling shutter problems. No moire and aliasing issues. XLR inputs means no double-system sound or Radio Shack kluges to construct. But these cameras have suddenly become uncool even though they are much better at handling the job of live events or run and gun documentary work.
Click to expand...

So wrong on all points:

1. "reduced us to using inferior equipment" We're talking original price $5,000 and up pro lenses here. The better SD lenses are perfectly capable of resolving HD, as seen in my footage and will be proven without a doubt in the link at the end of this message. Some say that only high-end test equipment can tell the difference.

2. "Lenses won't cover the entire GH2 sensor, so you'll get vignetting". Completely wrong, the image circle covers the full sensor using the built-in 2x extender with NO vignetting at ANY focal length. Or use it with the GH2 1:1 crop mode in 1x. The GH2 1:1 "crop mode" equates to a 1/2" sensor size and ANY 2/3" B4 lens provides more than full coverage with NO vignetting.

3. "you're going to get chromatic aberration" Chromatic aberration is not a real issue unless you are only shooting resolution charts all day. "Shoot people, not charts". Do you see any CA problem in the footage I shot?

4. "You need to stop down quite a bit to avoid either roaming aperture or softness" The band footage I shot was with the lens WIDE OPEN, in existing low light. I kept it that way ALL NIGHT, zooming all the way in and all the way out & it maintained exposure and sharpness. Oh yeah and it does get even sharper stopped down. That's a good thing.

5. "No powered zoom" Wrong AGAIN, did you even read my post? quote: "I also put together a cable and battery to POWER THE ZOOM ROCKER ON THE LENS." One hand on the powered zoom and one to focus. But the footage I posted was shot even before I built the zoom cable. I just used a zoom / focus assist 'stick'... and found it quite easy, and besides, one of my main points is, lens is PARFOCAL: it STAYS in focus as you zoom! So much for the "1970's documentary aesthetic".

6. "The smaller chip gives you deeper DOF". Exactly. That's the VIDEO LOOK we're trying to AVOID. Cinematographers are after the FILM LOOK which means LESS depth of field. That is precisely why independent cinematographers are flocking to the large sensor GH2 and AF100.

7. "so you aren't hunting for focus every time somebody in the shot moves". Cinematographers almost exlusively use manual focus so "hunting" is not an issue.

8. "(prosumer camcorders) have an ISO between 400 and 800". The 4/3" sensor has 16 TIMES the area of a little 1/3" sensor consumer camcorder, which means that at the same ISO and exposure setting it's collecting 16 times as many photons. So gain and signal-to-noise ratio is four stops better on the 4/3 sensor at the same ISO. Translated, this means that noise/image quality at ISO 400 on a 1/3 "prosumer" camcorder is equivalent to the noise levels at ISO 6400 on a 4/3 GH1, GH1, or AF100.

9. "Moire and aliasing issues" It's well documented that the GH2 and AF100 are optimized for video and have eliminated the moire and aliasing issues that plaque other DSLRs. This IS a GH2 forum, by the way.

10. "Rolling shutter" Remains an issue with CMOS sensors but can be minimized with proper camera technique and pretty much eliminated in post with several plug-ins. We are GH2 users here and we know this.


So, basically you're complaining that a $500 SD "old broadcast lens" isn't as good as a $20,000+ HD Cine lens? Who ever said that was a realisitc comparison, and how many people shooting video with a $800 GH2 can afford a $20,000+ HD video lens ???

Well, believe it or not, an "old SD broadcast lens" actually holds up quite well vs. a $28,000 HD cine lens.
This site compared test footage shot with an "old SD broadcast lens" using the built-in 2x extender vs. a very expensive HD Cine lens combined with a $5500 optical adapter designed to correct CA... and guess what? The "old SD broadcast lens fared VERY well. See for yourself:

http://gearjones.com/2011/09/15/abel-cine-hdx2-vs-mtf-b4-to-micro-four-thirds/?pid=12
 
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When I was shooting on an SDX900 years back we tested the SD servo zoom against an HD servo zoom.
The quality of the glass was like night and day, yes the HD lens was that much better.
 
David W. Jones said:
When I was shooting on an SDX900 years back we tested the SD servo zoom against an HD servo zoom.
The quality of the glass was like night and day, yes the HD lens was that much better.
Click to expand...

Well a $20,000+ lens had better be sharp! Otherwise what are you paying the big bucks for?
This is a GH2 forum, right? I don't expect many GH2 owners are going to run out and buy a $25,000 HD Cine lens for their $800 camera.
But some of the better SD lenses hold up VERY well... particularly against consumer SLR zoom lenses. Take a look at the link I provided in last post.

My response was to the OP who was complaining that "The panasonic lens does not maintain focus and iris as you zoom" when set at "manual everyting". I find the B4 video lenses to be a viable and affordable solution. I am open to comments on the quality of the footage I posted but saying that a $500 solution is not as good as a $25,000 lens is not really relevant or helpful.
 
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dishan said:
But they're SOOO uncool! ;)

All kidding aside, I'm actually planning on using my GH2 for an outdoor documentary-style shoot simply because I don't have to shlep my larger camera with me on a hike.
I've also managed to get it into places that they wouldn't allow a full sized camera, so there is merit to using them when you can, although you have to put up with an admittedly compromised workflow.

But I'm having second thoughts now because of lens selection- I have a thread in the DSLR general discussion here: http://www.dvxuser.com/V6/showthread.php?271235-Equipment-recommendation-for-outdoor-docu-style

Trying to determine if using the kit 14-45mm lens at F/8 will still noticeably "step" the aperture as I zoom, because I could really use the IS on a shoot like this. I really wish there were a constant aperture zoom with IS for M4/3rds that wasn't as ridiculously expensive as those Olympus ones.
As far as parfocal- is that the same as "internal focus"? Someone recommended I look into a vintage F/3.5 zoom since there are many of them with internal zooms. Obviously, I'd be losing IS so I'll need to be more stable, but will that let me zoom and keep focus? Or does one have nothing to do with the other?

Also, Turbodog, that lens looks really cool mounted on the front of the camera (shows you mean business), but the footage just looks OK. Once you are losing that much light with the extender, one can't help but start to wonder if a vintage manual zoom wouldn't be cheaper and better looking. Man, there is some serious jello/jitter at one point as well!
Click to expand...


"As far as parfocal- is that the same as "internal focus"? -- No those are two different things. Internal focus means that the lens doesn't extend and the front element doesn't rotate, as you focus. Parfocal means it stays in focus as you zoom, per the OP's question. Some internal focus lenses are parfocal and some parfocal lenses are internal focus... others are just one or the other and cheap consumer zooms are neither. They are not dependent on one another.

"Once you are losing that much light with the extender, one can't help but start to wonder if a vintage manual zoom wouldn't be cheaper and better looking." You are only losing light to f/3.4 fixed aperture with the 2x extender. That is across the whole zoom, which is better than any of the Panasonic zooms, plus it's parfocal and you can power the zoom rocker. Or you can use it in the 1:1 crop mode on the GH2 and get true F/1.7. Stopped down to 2.8 it's looking good.

"the footage just looks OK" What's wrong with it, specifically? I think it looks pretty darned good, considering this was shot in a dark club with the lens wide open. "35mm equivalent" focal length 34-476mm. Fixed aperture. Parfocal. Servo zoom capability. Name a lens for under $1000 that can do all of that better than this.
I'm very happy with the footage as are the guys in the band. The singer said it was the best video anyone ever shot of him. And this is only YouTube quality, about 6 mb/s. I love the way it looks on my Plasma TV without the YouTube compression; with the hacked GH2 at only 30 mb/s it has a very film-like quality. And it gets sharper if you light your scene properly and stop down a bit.

"start to wonder if a vintage manual zoom wouldn't be cheaper and better looking". I tried that. I picked up a 28-70mm f/2.8 for Canon FD mount on eBay. First of all something like that is much harder to find, and not neccessarily cheaper. Yes the image quality is very good, but, it's not parfocal and it's not a video lens so the zoom is not as smooth. Not to mention you can't power the zoom like you can with the B4 lenses. A vintage slr zoom is fine for use as a variable prime, but if you're zooming while shooting, it's not a good solution.

"Man, there is some serious jello/jitter at one point as well!" That's only because I bumped into the tripod at one point. Sheesh. What does that have to do with the lens performance?

"I really wish there were a constant aperture zoom with IS for M4/3rds that wasn't as ridiculously expensive as those Olympus ones." -- Don't we all, my friend? Don't we all. (And remember the Olympus lenses are NOT even IS. The IS is done in the Olympus cameras, not their lenses.)


My conclusion is that for the price the B4 lens/adapter is a a really nice tool to have, along with some SLR primes and zooms. It's way better than any C-mount lens.
I've got all the Panasonic MFT lenses, and they're fine for outdoors in bright light, and for photography, but they're my least favorite video lenses, except the 25mm f/1.4 which is quite nice, but limited.
 
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Turbodog said:
So wrong on all points
Click to expand...

1."The better SD lenses are perfectly capable of resolving HD. Some say that only high-end test equipment can tell the difference."

My own tests say otherwise. I was the promo videographer for a local news station, where I made the switch from an SD Beta SP camera to an HD JVC HD250. I did a comparison between the old SD Canon broadcast lens and the Fujinon HD lens and there was a noticeable difference in resolution. When I got my GH1, I did a lo-tech, jerry-rigged test and put the SD lens on it, using the 2x extender, etc. It didn't look good. Granted, I didn't have a real adapter.

2. "the image circle covers the full sensor using the built-in 2x extender with NO vignetting at ANY focal length. Or use it with the GH2 1:1 crop mode in 1x."

My experience with 2x extenders is that they degrade the image and make it look low-contrast and milky. And the GH2 crop mode is great, but that eliminates the shallow DOF advantage of the GH2, and makes the image more noisy by about 2 stops, yes?

3. "Chromatic aberration is not a real issue unless you are only shooting resolution charts all day. "Shoot people, not charts".

Yes it is a real issue. It's something I had to contend with everyday with broadcast lenses. Open up any wider than f4 and highlights looked cyan and magenta instead of white. No amount of lens shading or CA correction could fix it. It looked even worse when put on a CMOS camera.

4. "The band footage I shot was with the lens WIDE OPEN, in existing low light. I kept it that way ALL NIGHT, zooming all the way in and all the way out & it maintained exposure and sharpness. Oh yeah and it does get even sharper stopped down. That's a good thing."

My post wasn't specifically aimed at your post. I was referring to the Panasonic kit lens with its variable aperture, and to the tendency for 35mm still lenses (which are the most commonly used lenses for DSLR video shooting) to be softer when wide open.

5."I also put together a cable and battery to POWER THE ZOOM ROCKER ON THE LENS." One hand on the powered zoom and one to focus."

That's my whole point. In order to get the same performance as a prosumer camera, you had to go DIY and make that. So now you have a behemoth lens on the front of a little DSLR, and probably need rods or some kind of lens support to properly balance the camera on a tripod. Can you go hand-held with that thing without using a rig? More money and time spent putting together support gear that would be unnecessary with a camcorder.

6. "That's the VIDEO LOOK we're trying to AVOID. Cinematographers are after the FILM LOOK which means LESS depth of field. "

I know. Which is also part of my point. That the "cool-factor" of shallow depth-of-field can work against event videography because it's more difficult to keep an unpredictable subject in focus. Also, the FILM LOOK is about bokeh. And I don't like the bokeh on broadcast lenses. Their apertures create a bokeh that looks like VIDEO, not to mention the lens flares look like video because the optical elements inside remind us of broadcast lenses, not film lenses. So there goes the film look.

7. " Cinematographers almost exlusively use manual focus so "hunting" is not an issue."

I didn't mean auto-focus hunting. I meant heaving to constantly manually pull focus. I've seen a lot of out of focus video since DSLRs arrived. That's the downside of shallow DOF.

8. "So gain and signal-to-noise ratio is four stops better on the 4/3 sensor at the same ISO. Translated, this means that noise/image quality at ISO 400 on a 1/3 "prosumer" camcorder is equivalent to the noise levels at ISO 6400 on a 4/3 GH1, GH1, or AF100."

This is just not true. My GH2 set to 6400 ISO is not going to look less noisy than a prosumer 1/3" camcorder at 400 ISO.

9. "It's well documented that the GH2 and AF100 are optimized for video and have eliminated the moire and aliasing issues that plaque other DSLRs. This IS a GH2 forum, by the way."

True. The GH2 rules. I was talking DSLRs in general, but you're right when it comes to the GH2.

10. "Rolling shutter" Remains an issue with CMOS sensors but can be minimized with proper camera technique and pretty much eliminated in post with several plug-ins."

Which again proves my point. The limiting of camera moves based on a technical side-effect not present in prosumer CCD camcorders is a negative thing. And having to fix shots in post with a plug-in is another negative.


"So, basically you're complaining that a $500 SD "old broadcast lens" isn't as good as a $20,000+ HD Cine lens? Who ever said that was a realisitc comparison, and how many people shooting video with a $800 GH2 can afford a $20,000+ HD video lens ???"

No, I was comparing a $500 SD "old broadcast lens" to the built-in lens of a $3,000 to $5,000 prosumer CCD camcorder.

Other things I didn't mention were ND filters. With a prosumer camera, you flip a switch and in an instant you've got ND. With a broadcast lens, you'll need to buy a set of 82mm ND filters, which aren't cheap, and constantly take them on and off. Or buy a mattebox and a set of 4x5 glass ND filters, which isn't a cheap option either.

Hey, I've bought all this stuff. I own a GH2 and have invested in my rig, etc. My point is that for run and gun work, or event videography, the hoops that you have to jump through in the name of shallow DOF are enormous.
 
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