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View Full Version : Playing with long shutter speeds and "30p"



lordtangent
2007 September 21st, 04:44
I was thinking about the long shutter speeds and it occurred to me that of course, when you shoot with a shutter speed like 1/6 of a second you are by necessity shooting at 6 frames per second. It's pretty obvious, but I got excited anyway once I understood the ramifications. It's a very easy way to "under crank" the camera! The only side effect is since the HV20 only record 24 or 60 distinct images per second, you get that "steppy" effect where it duplicates the frames to fill the time. No problem... frames are easy to throw away...

I came up with an AVISynth script which uses the FDecimate plug-in to automatically remove the extra frames and re-time the clip to 23.976 FPS. It works great. Of course the end result produces frames that have what amounts to a 360 deg shutter. For under cranked effects it looks pretty cool though, at least IMHO.

One thing I figured out, which I'm not sure anyone else has mentioned explicitly, is that if you use a 1/30th of a second shutter speed the HV20 effectively produces "30p" also. Again, the shutter time is an "unnaturally long" 360 deg and some people might not like the look. But at least to my eye it looks much nicer than 60i. And of course, the 1/30th sec shutter speed is also an entire stop of exposure more than 1/60th. One stop is a lot when you need it. I'd rather have a 360deg shutter and sort of long-ish motion blur than have to resort to using gain any day. But I'm thinking I might shoot in this "30p" mode under regular circumstances. It's a nice way to split the difference between 24p (and all the hassles involved) and 60i (with it's not too filmic field based structure) I'm going to do more tests.

Here is an unprocessed .mt2 clip at "30p"
http://hv20.info/yopu/30p.m2t

It's a little shaky because it was so freaking windy when I shot it my light little tripod was actually shaking!

Here are some shots done at 1/6th sec and then processed to remove the extra frames from the .m2t stream.
http://hv20.info/yopu/24p_from_6p_1.mp4
http://hv20.info/yopu/24p_from_6p_2.mp4
http://hv20.info/yopu/24p_from_6p_1_QT_encoded.mp4

I encoded them with AVIdemux to h.264. A buddy of mine raised a flag that Quicktime chokes on my AVIdemux encoded frames. I'm not too wild about Quicktimes encoder (more on this later) so if you want to watch my clips I suggest you try Mplayer or Media Player Classic. Trust me, you'll like them. They both happily play stuff both Quicktime and Windows Media Player choke on and being Free Software, neither is used as a front end to sell you "iTunes" or other crap like that.

I also encoded clip #1 with Quicktime. For anyone who already has Mplayer I urge you to compare the QT compressed and the x264 (via AVIdemux) encoded files. QT totally mutilates the color. This is a good example of what I mentioned in one of my other threads regarding "video" color space vs. full range. QT seems to assume you WANT the blacks padded and there does not seem to be any way to turn that behavior off. AVIdemux, on the other hand, encodes what you hand to it without messing with the color too much. (not only that but it's much more flexible and tweakble in other areas)

Comments? I'm really interested to learn any other tricks people have figured out with the HV20 and also what other people are using for encoding their final output.

SenorKaffee
2007 September 21st, 06:59
Hmm - itīs not really 6 frames mapped on 24 frames or 60 frames, you just introduce more and more motion blur.

For the scene it looks really nice. So this is basically 4x the original speed now?

Flyingsheep
2007 September 23rd, 03:17
Hey, nice ideas. I was also thinking about recording at 1/6th shutter, getting rid of the duplicate frames, and speeding it up to 24p. I believe it can make cool results that aren't useless at all. Plus, you can record a scene at 1/6th of a second that has zero movement, place the camera on a tripod, and you'll get really really good low light shots without noticing it being 6 frames per second. I'm sure this can be useful for something.

Garnt
2007 September 23rd, 23:39
How are you able to manually adjust shutter speed on the HV20?

lordtangent
2007 September 24th, 18:30
Hmm - itīs not really 6 frames mapped on 24 frames or 60 frames, you just introduce more and more motion blur.


I'm not sure what you are getting at. It's exactly what you say it isn't... after post processing of course. The camera must hold each frame shot for 4 frames recorded to tape just to keep in sync with the fixed frame rate of the tape though. You need to take them out in post.

The only real caveat is that in order to get these "frame rates" you absolutely must use a shutter speed equal to the frame rate you want, which in this case is a very long shutter speed that will produce long motion blur. (IMHO this is what you want to emulate "time laps" or slow frame rate) If you want to just speed things up, shoot at whatever shutter speed and just throw away frames.

My point from the beginning is that by doing it this way you get a shutter speed that corresponds to the frame rate. It's a "feature" in this context.

lordtangent
2007 September 24th, 18:33
How are you able to manually adjust shutter speed on the HV20?

Shutter priority manual mode. It's labled "TV" You can find more info about it in the manual. IN this mode the camera is still mostly automatic and will still set the exposure for you using aperature and gain. But you can also still also lock exposure and use exposure compensation to get the exact exposure you want.

Felix
2007 September 25th, 00:01
Very nice results. I think I'm gonna be using this "30p" a lot from now on.

Thanks for the tip!

orbitaljon
2007 December 10th, 16:08
btw....if you put the camera into photo mode, you can still record the footage to a laptop via firewire, and then gain the control of the photo shutter speed of 1/2 instead of the 1/6 limitation in tape mode.

jmalmsten
2007 December 10th, 17:37
btw....if you put the camera into photo mode, you can still record the footage to a laptop via firewire, and then gain the control of the photo shutter speed of 1/2 instead of the 1/6 limitation in tape mode.

You have a guide, or a link to one, that gives the programs used for this... I've just the other day started thinking about doing some kind of Motion Control and a feature like that would really help things out... I just would have to figure out a way to physically move the camera with a custom-program though... but I've seen it done before and with some basic electronic skills I'm sure I could learn to build one...

nice effect though in the 24p-compressed clip (haven't seen the other ones). I really need to get out and do a test of walking around with my HV20 in the forest with some stabilization doing a similar thing just to try out one of those effects I have always heard about from the makings of Return of the Jedi and Firefox;)