soft focus w/ the dvx100

Annie Wengenroth · February 7, 2005

So I recently shot a documentary in which the footage looked focused IN camera, but then when we transferred it into Symphony, the closeups (in which I'd zoomed in) looked slightly out of focus. I've heard about this happening with the DVX but am still not clear as to why it happens- are there any ways around it? I find when I'm zoomed in past about 90%, there's just no way to get adequate focus. Is this just a bad design or am I missing something? I'm getting kinda frustrated, I was starting to feel like I was finally learning to work with every aspect of this camera, even the shortcomings, and this has thrown me for a loop. Any tricks?

If anyone has specific questions about which settings I was using, I can tell you exactly because I wrote them down. We were in 24P mode with the cine-like gamma quality, no gain, -4 on the detail. The focus and aperture were both set on manual. Has anyone else had problems like this or is it just me? ;)

Edited February 7, 2005 by SpikeyAnnie

Stas Tagios · February 7, 2005

So I recently shot a documentary in which the footage looked focused IN camera, but then when we transferred it into Symphony, the closeups (in which I'd zoomed in) looked slightly out of focus. I've heard about this happening with the DVX but am still not clear as to why it happens- are there any ways around it? I find when I'm zoomed in past about 90%, there's just no way to get adequate focus. Is this just a bad design or am I missing something? I'm getting kinda frustrated, I was starting to feel like I was finally learning to work with every aspect of this camera, even the shortcomings, and this has thrown me for a loop. Any tricks?

If anyone has specific questions about which settings I was using, I can tell you exactly because I wrote them down. We were in 24P mode with the cine-like gamma quality, no gain, -4 on the detail. The focus and aperture were both set on manual. Has anyone else had problems like this or is it just me? ;)

<{POST_SNAPBACK}>

Could be a number of things...

Were you using a monitor during production to check framing and focus? Since it was a doc, I'm guessing you were shooting run-and-gun, without a monitor. Judging focus via the LCD and/or viewfinder doesn't always produce perfectly focused images, since neither are hig res enough to always accurately judge focus. Are you using the DVX-100 or the DVX-100A? The 100A has a peaking control for the VF that should make it slightly easier to judge focus by.

You camera could be suffering from a back-focus problem, which would require factory adjustment; try checking it with focus charts or some subject that's easy to tell if it's focused. Zoom in, focus, zoom out, and see if the focus holds or if the focus drifts. If it drifts, it could be a back focus issue.

How close was your subject in the out of focus shots? The camera has a minimum focus distance that will prevent you from focusing at close range, especially at the longer end of the zoom.

Were you using the anamorphic adapter? The anamorphic not only needs to be properly mounted and adjusted on the camera, but also limits the focal lengths and apertures at which you can get sharp focus.

An odd problem I've got with my DVX-100 is that the image briefly goes out of focus in the middle of any snap zoom. Can't explain it.

Back in December I did several weeks shooting on a short film I'm directing, and now that I'm cutting the footage, there are several shots where the focus on CU's is soft, like the problem you describe, but I attributed the problem to not having checked the focus before the shot, which sometimes happens when you've only got a crew of three and we're all doing multiple jobs.

Other than that, I've had no focus issues with my camera.

Hope this helps. :)

Phil Rhodes · February 7, 2005

Hi,

> Judging focus via the LCD and/or viewfinder doesn't always produce perfectly focused images

Seconded.

> You camera could be suffering from a back-focus problem, which would require factory

> adjustment;

Given the way the lens on the DVX works, I don't think that it could really have what would be considered to be a back focus problem. It's a servo-tracked zoom, so the automatics should just deal with it (Presumably a cost saving for Panasonic when commissioning newly-manufactured cameras.)

> try checking it with focus charts or some subject that's easy to tell if it's focused. Zoom in, focus,

> zoom out, and see if the focus holds or if the focus drifts. If it drifts, it could be a back focus issue.

....which is worth trying notwithstanding my feeling about the way the zoom works. I guess the thing can still be bent.

> An odd problem I've got with my DVX-100 is that the image briefly goes out of focus in the middle of

> any snap zoom. Can't explain it.

Okay, this is the crux of the whole thing and understanding why this happens, or at least why I presume this happens, is crucial to understanding how the lens on the DVX-100, and many other modern consumer zooms, work. I've said this once in another thread, but I'll repeat it briefly here:

On a conventional zoom, there are three groups of lenses (excluding any relay groups to put very short focal length images deeper into the colour splitter block.) Usually you're moving one of them to zoom, often the middle one, and one of the others to focus. Because of the complex relationship between focal length and focus distance there's generally a mechanical connection between the various components, usually a curved track inside the lens which causes them to move in a carefully predetermined manner. This piece of engineering has to be manufactured very precisely, or the zoom won't track focus properly, even when the back-focus is correctly set. This is expensive and complicated, but it's how your average zoom lens works, including SLR lenses, ENG zooms and anything else which has a solid mechanical connection between the controls and the lens groups.

The alternative way of doing things, used by practically all consumer video cameras including I presume the DVX-100, is to mount all the mobile lens groups on servoactuated tracks and have a microcontroller system constantly calculate the positions everything should be in to maintain a given focal length and focus distance. This makes for a big design effort, but it's cheap to replicate, since your microprocessor system can be made to inherently allow and compensate for engineering tolerances. This makes the camera affordable, but has several side-effects:

- The lens doesn't really have any such thing as back-focus. Limitations in the way the electronics work may require Panasonic to do some setup on the camera before it leaves the factory, but that's more to do with teaching the electronics where this particular zoom is in the range of engineering tolerance than it is conventional backfocus adjustment.

- There can't be any such thing as a proper manual control for either focus or zoom - you can only program the microcontroller as to where you want the focus or focal length to be. This doesn't inherently mean you can't have absolute focus distances and an absolute relationship between the focus distance and the position of the ring that's used to encode it, although most implementations - the XL1 most notoriously - have done it that way because it allows them to use cheap magnetically-coupled rotary encoders which don't have a linear relationship between encoded position and actual position if you don't always move the ring at exactly the same speed. The DVX-100 does this differently, possibly using an optical encoder or something like that.

- If you move either the focus or the zoom very quickly, the other attribute may appear to change slightly as the system tries to keep up. Generally this applies to focus during snap zooms - what you're seeing, and what leads me to believe the DVX-100 uses this lens scheme, is the slop in the servo loop. It may also be that the focus servos are just slower than the zoom servos.

None of these considerations should mean you get soft images, unless there's a fault with the camera, you're within minimum focus distance, or you simply didn't set the focus correctly.

Phil

Annie Wengenroth · February 7, 2005

Hm...okay...we used the 100, not the 100a, we didn't use a monitor and didn't have the focus charts on hand but I'm looking at them now and starting to realize that maybe I was a little bit too close. We were actually going to use the anamorphic lens adaptor but actually decided against it at the last minute. And as far as I know, it was a camera that hadn't even been put into circulation yet at school so I would assume that no one had ever shot on it before, meaning that there probably aren't any problems with it.

What about filters, would that have thrown anything off? We had a Super Mist clear on there. It's looking like the focus issue is simply an issue with the camera that I hadn't thought would come up, until I was told "Get in as close as you can"...so in the heat of the moment, I got right in there, about two and a half to three feet away, zoomed in maybe 90%.

How frustrating. Oh well. Guess I'll just chalk it up as one of those "learning experience" types of things. Better to know now on a student documentary than in a higher-pressure situation. Other than the soft-focus issue I thought the DVX performed very well and have even found that I've finally gotten used to shooting handheld on this baby, so that's cool.

My saving grace, I guess, is that some of this was b-roll and not the actual interview and the director wanted an "abstract, soft" look. Though it would have been nice to have had a "real" zoom lens. At least now I can properly explain what happened without looking like an idiot. Thank you for the explanation, Phil. But DAMN it drives me crazy! Stupid computer chips. ( Gee it could be worse, at least the camera's not running Windows. :rimshot: )

Stas Tagios · February 7, 2005

What about filters, would that have thrown anything off? We had a Super Mist clear on there. It's looking like the focus issue is simply an issue with the camera that I hadn't thought would come up, until I was told "Get in as close as you can"...so in the heat of the moment, I got right in there, about two and a half to three feet away, zoomed in maybe 90%.

<{POST_SNAPBACK}>

The minimum object distance of the original DVX is around 3 feet, so that could be your problem; anything three feet or closer and you're limited as to how close you can zoom in without losing focus. On the DVX-100A, the MOD has been shortened to around 1.5 feet.

Filters shouldn't affect your focus, unless of course, you're using a something like a soft focus filter, which would make it harder to determine proper focus.

Phil, yeah, the bane of consumer and prosumer video lenses are the all-electronic/electro-magnetic servo controls, to be sure, though as you point out, the DVX lens offers the most nimble control of any fixed-lens camera in its price range... the odd thing is that some DVX's don't exhibit the brief "de-focusing" during snap zooms, which is why I initially discounted the defocusing as being a by-product of the lens's electronic insides. Now I haven't done official-type lab tests, just tried snap zooms on various DVX's besides mine at trade shows and camera shops, but some maintain focus during the snap, others don't. Weird.

Aside from the snap zoom issue, I find that the DVX's lens has a lot more finesse that most of the others in its class, especially the Sony offerings (PD-150, 170, etc.), the servo control of which is far sloppier (and makes it impossible to do an accurate snap zoom; try it on the new Sony HDV and the lens takes a noticeable fraction of a second longer to arrive at the long or wide end after you snap the "manual" zoom ring. Really lame.

As for the back focus issue, I mention it only because I recall reading somewhere (perhaps on this forum) that some people had focus problems with the DVX, and that it wasn't holding focus through the zoom range, which it should do. Of course, as you mention, the DVX lens isn't constructed like a normal ENG or cine zoom, and obviously doesn't have a traditional means of adjusting the back focus, but given the small size and complexity of the lens construction, perhaps some malfunction with the servos or electronics could result in a problem resembling back focus.

Phil Rhodes · February 7, 2005

Hi,

What was your A camera?

By the time you've got a mist filter on an already-soft little camera like a DVX, it's going to look pretty mushy anyway. I'd avoid diffusion like the plague on a camera like that. If you're cutting against film, an SDX-900, digibeta or some other up-market toy, it's going to look soft.

Phil

Annie Wengenroth · February 7, 2005

We had 2 DVX's and we're actually going to be manipulating some of the b-roll in After Effects to some degree, though I'm not sure what the final result will look like because I'm not involved in it. Well, I don't feel too bad about the whole thing; it's a pain but now I know a) why it happens and B) what to do to avoid it. And it still hasn't stopped me from wanting a DVX100a so there ya go!

nchopp · February 8, 2005

Hi,

What was your A camera?

By the time you've got a mist filter on an already-soft little camera like a DVX, it's going to look pretty mushy anyway. I'd avoid diffusion like the plague on a camera like that. If you're cutting against film, an SDX-900, digibeta or some other up-market toy, it's going to look soft.

Phil

<{POST_SNAPBACK}>

I disagree. While a soft-filter might be a bit much, some VERY moderate diffusion can do wonders with DV. That's one of the killers about DV - it's too sharp. The edges are too hard. (If you're trying to compare to film, at least)

Phil Rhodes · February 8, 2005

Hi,

Right, so video, a lower-resolution medium than film, is too sharp?

I guess this works the same way as "it has low dynamic range" and "it looks flat."

One or the other...

For the record what your'e seeing is probably edge enhancement, which can be moderated on the DVX-100.

Phil

nchopp · February 8, 2005

Hi,

Right, so video, a lower-resolution medium than film, is too sharp?

I guess this works the same way as "it has low dynamic range" and "it looks flat."

One or the other...

For the record what your'e seeing is probably edge enhancement, which can be moderated on the DVX-100.

Phil

<{POST_SNAPBACK}>

Well, if you're blowing up to film, you're obviously going to need all the sharpness you can get. I was referring to DV itself. And low dynamic range - well, yeah. :)

Phil Rhodes · February 8, 2005

Hi,

> Well, if you're blowing up to film, you're obviously going to need all the

> sharpness you can get

Yes, but sharpness is not edge enhancement. Video is soft when blown up. What're you trying to say here?

Phil

nchopp · February 8, 2005

Hi,

Yes, but sharpness is not edge enhancement. Video is soft when blown up. What're you trying to say here?

Phil

<{POST_SNAPBACK}>

Yeah, I guess I'm not expressing myself very well here. If you're just screening something DV (that, say, went straight to DVD), you get the overly sharp look of, well, video. I don't really know how to define it. Since we're talking about 24 here it's not the frame rate, it's just the way video... looks.

Phil Rhodes · February 8, 2005

Hi,

It's not correct to call it overly sharp, especially when it's probably overly soft - there are even SD cameras that are a lot sharper than a DVX. You're seeing edge enhancement. It's ugly. Turn it off.

Phil