What happens at 1/30 shutter speed at DVinfo.net

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Old August 16th, 2003, 09:37 PM   #1
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What happens at 1/30 shutter speed

I am just musing here for a moment.

If the VX2000 is running in standard interlaced mode it is capturing approximately 60 frames per second. So what happens when the shutter is set to something lower than 1/60? It would seem to me that with the shutter moving at this speed the camera coule only capture 30 frames each second or am I missing something here? I am not a technical genius at video so I may be totally in left field.
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Old August 16th, 2003, 09:55 PM   #2
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The shutter speed has nothing to do with the framerate.

First off, it's not capturing at 60fps, it's capturing at 30i (interlaced) which means that it's 30fps, with 2 fields per frame, thats why it's "interlaced", and it will always capture at that framerate, no matter what the shutter speed is, unless you put it into 15fps progressive mode, of course.

Basically the shutter speed, in my words, is how fast it "refreshes" to capture the light. On film cameras, it's a mechanical shutter, but on dv cameras, it's electronic. Say you set the shutter speed at 1/8000, what will happen, is that anything moving will be very sharp, when you pause a frame, whereas at standard 1/60 it would blur. Also, the big thing about shutter speeds, is at a fast shutter speed, you need a lot of light to get it exposed properly. The only reason to use slower shutter speeds (under 1/60) is in "low light" situations, and the slower the shutter speed is, the more light the CCD(s) will be able to gather, giving a brighter image, but at the same time, the slower you go, the more motion sensitive it is, meaning everything will blur, and it will get "stroby". You can also use slow shutter speeds for some cool effects sometimes...

Here's a better definition, at dpreview, it's for digital cameras, but pretty much the same thing:

http://www.dpreview.com/learn/Glossa...r_Speed_01.htm
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Old August 16th, 2003, 11:19 PM   #3
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Fast shutter speeds also yield
"strobey" motion. I tried taping at 1/180 and faster to help me produce less blurry stills of martial artists swinging sticks. The trade-off was that one could actually see the stick moving around as if under a strobe light.
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Old August 16th, 2003, 11:38 PM   #4
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Hmmm, thats not normal, Gints, where you under flouresent lights by any chance?
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Old August 17th, 2003, 06:27 AM   #5
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Actually This is something which has recently interested me as well. Alex, I don't think you're quite right here. If you set the VX-2000 shutter to 1/30 you will be getting sort of a "pseudo progressive" image. You can verify this by looking on a monitor at a frame where there's motion. At 1/60 sec you will clearly see the interlace effect. At 1/30 you will not. There are two trade-offs however. First, at 1/30 there's more blurring since it's a slower speed. And second, both fields will be the same, so you have reduced your vertical resolution by 50%. But the image will appear sharper.

I got interested in this subject a few days ago while shooting just after sunset. I dropped the shutter speed on my PDX-10 to 1/30 to shoot with a wider lens opening. When I looked at the footage later I liked the results, and also noticed that it did not appear interlaced. This led me to apply a technique to some of my other shots (taken at 1/60 sec) by stacking two tracks in FCP, de-interlacing the odd field on the bottom track and the even field on the top track, which I also made 50% opaque. This produces a similar image to the 1/30 sec footage and stills do not appear interlaced. However it does give a softer image.

After doing some research, I stumbled across Marcus van Bavel's comments in an article right here at DV Info Net. This led me to DVFilm Maker. I did some tests with their free version and liked the results. It manages to provide higher resolution de-interlaced frames by analyzing areas with motion and treating them differently than the static elements of the image. So I ended up buying a copy of this software and will plan to shoot at 1/60 sec for the rest of my project, then process the footage afterwards. This gives me the quality that I liked with the 1/30 sec shutter speed, but with better resolution.

Gints is also correct about the "strobey motion" at high shutter speeds. The whole idea of 60i is to smooth out motion by presenting alternate fields 60 times per second. At 1/60 shutter speed there will be just enough blur between frames for them to blend. But if you shoot higher speeds the individual fields have sharp images that are different. You eye can perceive this as separate images, giving that "strobey" feeling.

I'll admit there's a lot I don't know here - so if you have a deeper understanding on this topic please correct any of my errors! Here are a few interesting links that can tell you more on the subject:

http://www.100fps.com
http://www.creativecow.net/articles/...ing/index.html
http://www.race.com/dc/video/article.htm
http://www.ferrario.com/ruether/vid_....htm#pseffects
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Old August 17th, 2003, 10:25 AM   #6
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Boyd I used to use the same technique in FCP but Joes filters has a field blending filter which will give the same results if not better and you only need to apply it to one track without the need of stacking 2 tracks. Its also a tad bit faster render then the FCP de-interlacer.Joes Filters
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Old August 17th, 2003, 11:16 AM   #7
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Hi Boyd,

Thank you for your input and some very nice URLs.

The technique you mention is called "Field Blending". It can be employed in almost any decent NLE, but is very easy to do in FCP.
http://www.kenstone.net/fcp_homepage...ideo_film.html
http://www.kenstone.net/fcp_homepage...ffects_dv.html
http://www.kenstone.net/fcp_homepage/film_look.html
Matt also mentions some FCP plug-ins written by a very talented and all around good guy Joe Maller.
http://www.joesfilters.com

Field Blending does create a nice effect, but at the cost of resolution,,, it looks "soft", as you say.

The best techniques require rendering. Count on it and plan for that rendering time in your workflow. The best post-production solution is a subtle combination of a few different techniques.

Or, you could shoot in Frame Mode at 1/30th sec, which is by far a lot better than shooting at 1/30th sec on a camera without Frame Mode. Also, create an Image Preset on the XL1S or GL2: boost the Chroma just a wee bit, raise the Sharpness one, maybe two notches, drop the Blacks a level or two. I do this all the time anyways and add to that in post with a combination of Joe's Filters, including Joe's Frame Rate Adjuster set at 24fps and about 33% motion blur.
http://www.joesfilters.com/joesframerateadjuster.php
That may vary at times, depends on what the final venue is.

More in-camera techniques can be employed as well, which have been documented several times in the "Towards A Film Look Using DV" Forum.

- don
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Old August 17th, 2003, 02:35 PM   #8
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Thanks Matt and Don. Actually I downloaded the demo of Joe's Filters and there are a number of nice things there, actually quite a bargain - I plan to purchase the full version.

I decided to go with DVFilm Maker after comparing its results to the field blending technique you describe. It attempts to give you the best of both worlds by processing the static parts of the image differently from the moving parts. There are several other products that also do this (like Magic Bullet, FieldsKit, etc). But DVFilm Maker is a very simple, small standalone application that you can feed batches of files and let it run in the background (or on another machine). It also does a few other handy things like letterboxing as a bonus. I'll continue to investigate other options, but for under $100 it seemed like a good bet for the time being.

I'm shooting primarily with a Sony PDX-10 and VX-2000, so frame mode isn't an option, but your point about avoiding rendering is well taken. I think it's hard to generalize about things like sharpness and chroma, isn't it? I'm not familiar with the Canon's, so maybe there's a good reason though. To my eyes, recently I've been turning the sharpness all the way to the minimum. I really dislike the overenhanced edge look that tends to draw a cartoon line around everything. I find this to be especially true on the PDX-10. My current project will be projected on a 44' wide screen, and I'd rather have somewhat soft edges than see hard outlines or "shadows" around an object. Anyway, I can always apply sharpening in post, and think it's safer to do when I can view the image on a large monitor at home instead of through a viewfinder in the field.

Depending on what I'm trying to do I may either boost of lower the chroma (which Sony calls "color level"). For a sunset, or a shot of the sky, I might boost it to the max. In the fog on the beach the other day I took it all the way down for a more pastel effect.

So many choices, so little time! Makes it fun though :-)
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Old August 17th, 2003, 02:59 PM   #9
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Boyd,

Try this:

Set up your camera on a white poster board. On the poster board, draw a fine grid (much like grid paper) with a medium point Sharpie. Make the grid squares about 2" big or so. Now, fill the frame of your cam with the grid and view the image on a high quality external monitor. This should help you to see the amount of edge enhancement you have dialed in. If the sharpness is adjusted too high, you'll see the "cartoon line" anamoly you mentioned, somewhat of a 'ghosting' on each line. Dial down the sharpness until the lines of the grid are as resolute as you can make them with your camera's Sharpness control. By this I mean dial down the sharpness only until you see the severe edge enhancement ghosting go away and you see just the lines of the grid. There you go, that should be a good setting for you, I wouldn't recommend dialing down any lower than this as once you hit the Record button, your'e committed to that look. You can always soften your image beyond that with much more control in post. Joe's Filter's has some nice filters for this
http://joesfilters.com/joesdiffuser.php
http://joesfilters.com/joessoftspot.php
http://joesfilters.com/joessoftgradients.php

Let me know what you think,

- don
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Old August 18th, 2003, 02:35 PM   #10
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>Hmmm, thats not normal, Gints, where you under flouresent >lights by any chance?

Alex,

Yes, I'm under flourescent lights, but I'm using T8 ballasts which offer supposedly better flicker reduction than the usual T-12 ballasts. I'm recording
martial artists swinging sticks swung at full speed. Most swings
travel an arc that is recorded on 2-4 frames. These strikes are
fast. So, I'm not surprised that faster shutter speeds reduce the stick blur but increase the strobeyness.
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Old August 18th, 2003, 03:50 PM   #11
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easy to add motion blur and reduce strobing with Joe's Filter's in FCP

You can always re-introduce the amount of motion blur that you might lose with a higher shutter speed pretty easily with the two following Joe's Filters:
http://joesfilters.com/joesmotionblur.php
http://joesfilters.com/joesmultiframeblender.php

You can mix and match almost any number of Joe's Filter's as you see fit with FCP 3+, as Joe's FIlter's are exceptionally clean.

- don
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Old August 28th, 2003, 06:41 PM   #12
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The motion blur filters from revisionfx.com look a lot better than joe's filter for motion blur (although some of the other joe's filters are good).
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Old August 28th, 2003, 07:45 PM   #13
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I've been working a lot with computer animation over the past week or so, and had been frustrated in my attempts to make it look more realistic and match my live footage a little better. After much experimentation I realized that the lack of motion blur was the main culprit. I ended up buying Joe's Filters after playing for awhile with the demo, and would just like to second the good comments. Great package of effects, especially considering the price!

I've come up with a combination of frame blending and diffusion that I like pretty well. Depending on the source clip I vary some of the parameters. The motion blur filter itself didn't seem to do what I wanted.

The revisionfx filters also look nice, but it appears they require After Effects. Aside from the price, I'm just not up to learning that in the middle of a big project! BTW, the people at revisionfx really need a bigger font on their website, us old guys have a hard time reading that tiny type (or at least that's how it looks on my Mac under Explorer ;-)
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