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Trouble Getting Strings In Focus (seeing double)


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#1 Charlie Seper

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Posted 03 August 2005 - 09:39 PM

I don't know what on earth I do wrong but every time I try to work on my guitar instructional videos I have a devil of a time trying to get the strings to focus properly. Is there some magic trick to this? I've tried every kind of light in every intensity and aimed from every direction you could think of. I've tried one light, two, three, overhead, down under, everything and with two different video cameras. I've tried polarizers and ND filters of every variety, all to no avail. Everything else focuses fine; its just the actual strings themselves that always seem to be sort of doubled on screen, as if they're in motion, yet they look that way even while perfectly still. Some of you guys must have experience with taping/filming a musician playing a stringed instrument before. Is it this hard for everybody? Is there some trick I'm not aware of? I'm telling ya, the only time the strings ever look like they should is when the light is shining elsewhere. If they're in poor light then they look okay, however, they're then too dark to really see well. And being an instruction video, the light really has to be strong on the fretboard so students can get a close look at exactly what's being played. You simply have to have a lot of light. I'm sure it?s the metal of the strings that's causing the reflection/doubling problem. Aside from painting the strings flat black ( yeah?not cool) I don't know what the answer is. What's a guy to do? :blink:
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#2 sserge

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Posted 03 August 2005 - 10:14 PM

check out your shutter settings, I've shooted strings alot and had no problem on regular NTSC on 1/60

if you have still post it here, that's interesting
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#3 Charlie Seper

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Posted 04 August 2005 - 12:03 AM

I guess I can horse around with shutter speeds more than I have. I'm really not sure how that would change anything though if the strings look doubled even when they aren't movie. I mean besides changing the amount of light being let in the cam, which I've done a bunch of work with anyway through other means. But I'll try it.

I have an old freebee video that's been on a webpage for over a year. Its a little lower bandwidth but I think you can still see that there's a problem with the strings. Heck, I can even see in the still photo (that you click on) that there's a problem.

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#4 Chris Keth

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Posted 04 August 2005 - 12:27 AM

I guess I can horse around with shutter speeds more than I have. I'm really not sure how that would change anything though if the strings look doubled even when they aren't movie. I mean besides changing the amount of light being let in the cam, which I've done a bunch of work with anyway through other means. But I'll try it.

I have an old freebee video that's been on a webpage for over a year. Its a little lower bandwidth but I think you can still see that there's a problem with the strings. Heck, I can even see in the still photo (that you click on) that there's a problem.

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I honestly don't see what you're talking about in the instructional you posted. The strings show up single, not double.

I THINK what you may be talking about is aliasing. Since we're talking video here and also since guitar strings are generally slightly off-horizontal thin lines while the instrument is being played, aliasing is a big problem with them. Aliasing is the name for how slightly off-horizontal or off-vertical lines appear as stepped lines on video or in digital photos. In video, it's often really annoying, especially in this case, since the lines are always changing angle slightly and the steps keep changing. Unfortunately, there's no real way to get rid of it, since the problem is one the basic mechanics of working with video: the frames are made up of an ORDERED array of pixels.
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#5 Chris Cooke

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Posted 04 August 2005 - 12:41 AM

Try playing with different focal lengths. It's easiest staying in focus with a wide angle lens. Maybe even try macro when going for really tight closeups of the strings. That will put everything else out of focus but keep the strings sharp (don't move your guitar or camera). Don't use the auto focus feature on your camera because that will put the guitar in focus but not the strings. A couple little LED backlights inside the guitar body might give the strings a nice hilight that's easy to focus on. Also, the more you can get your iris closed down the deeper focus you'll have.
(I'm a guitar player as well, I've got a beautiful all graphite guitar called Rain Song.)
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#6 anamexis

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Posted 04 August 2005 - 12:45 AM

Well as Mr. Keth mentioned, it's really an issue of video resolution. The lower resolution, the more aliasing you experience. And as he mentioned, there's no real good solution, except to use a higher resolution (HD) or of course film.

This is the same phenomenon as you will find in zooming in on any digital image, it is just especially apparent on diagonal lines.
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#7 Charlie Seper

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Posted 04 August 2005 - 01:02 AM

Hmm...I'm not too sure about that guys. I've got a couple of old vids of Phil Keaggy that were shot on VHS around 1990 that look better than this. And the strings in my vids still have that dubbled look even when the guitar is sitting on the chair by itself (that's how I focus when I'm by myself here). But I'll try everyone's suggestions. I dearly hope its not a resolution problem. I don't see how it could be really because I have several VHS tapes that don't look like this, and my own stuff even has that twisted rope look even when viewing the DVD on a standard def set. I'll keep trying but maybe I'm stuck with it.

Thanks for all the suggestions.
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#8 sserge

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Posted 04 August 2005 - 01:46 AM

why not to shoot strings much closer than you did?
then, try to use pro camera which has diagonal DTL function which increase diagonal resolution and reduce moire

http://www.212film.com/bob/croton3.wmv

That shooting was on the edge of extended 21x canon lens and I was worried about softness on that magnification, so I didn't shoot strings so much, as usually I do.
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#9 sserge

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Posted 04 August 2005 - 02:07 AM

and
try to put any diffusion filter on your lens to spread out contrast of the strings, I thought that, tiffen low contrast should be works.
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#10 Chris Keth

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Posted 04 August 2005 - 10:40 AM

Hmm...I'm not too sure about that guys. I've got a couple of old vids of Phil Keaggy that were shot on VHS around 1990 that look better than this. And the strings in my vids still have that dubbled look even when the guitar is sitting on the chair by itself (that's how I focus when I'm by myself here). But I'll try everyone's suggestions. I dearly hope its not a resolution problem. I don't see how it could be really because I have several VHS tapes that don't look like this, and my own stuff even has that twisted rope look even when viewing the DVD on a standard def set. I'll keep trying but maybe I'm stuck with it.

Thanks for all the suggestions.

<{POST_SNAPBACK}>



What I was noticing was definately aliasing.

The VHS tapes you're talking about, how does he hold the guitar? If he holds the guitar so the strings are at a greater angle to the ground, then you wouldn't notice the aliasing nearly as much, even with the same video resolution.

There is a way to lessen aliasing in some video editing programs, as well as photoshop. What it really is, though, is a slight blur in the right places. I doubt it would help in this case since a slight blur on thin guitar strings would be very noticeable.

Here's something for you to try, since you said you do some stuff when you're at home alone: Shoot your guitar, in focus, with the strings at a 45 degree angle to the ground. Then shoot it with the strings almost, but not quite vertical. Then shoot it with the strings almost, but not quite, horizontal. Looking at the strings in these scenarios should demonstrate what I was talking about pretty well. The 45 degree one should look like the strings are straight lines, more or less, unless you do a digital zoom in. The other two, however, should look like steps, and should be very noticeable if the strings are very close to the vertical or horizontal.

Edited by Christopher D. Keth, 04 August 2005 - 10:45 AM.

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#11 anamexis

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Posted 04 August 2005 - 01:31 PM

Also, the low resolution of MiniDV would be more apt to alias than shooting straight to VHS.
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#12 Charlie Seper

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Posted 05 August 2005 - 01:04 PM

I tried all kinds of angles, it just doesn't seem to matter.

Maybe moving the camera in closer rather than using the zoom at all will help. I'm not sure. Shooting in progressive frames works but it leaves things a little blurry. What I really need to do is find a way to take the shine off the strings. Maybe some talcum powder will work.

I want to stick with my own cams for this (standard def) so I can work whenever I want and leave them mounted on their tripods in the studio. Also, if I rent hi-def cams then it would be difficult for me to edit since my computer isn't really good enough for hi-def footage. Its a typical 2gig processor and no raid arraid disc or anything. Its fine for standard def work but that's all. I may get into HDV next year, in which case I'll have to upgrade my box, but until then I'm sticking with what I've got. There's got to be a way to do this. I haven't tried screens for diffusing yet because I don't have any. I was always fine with reflecter boards and ND filters before, but I just may try putting the lights through a screen. I've got a feeling that this will solve the problem. I'm gonna try moving in closer first though.
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