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View Full Version : Clarification on 720/60P and 1/50, 1/40, 1/30 shutter



Kholi
05-07-2009, 05:39 PM
Okay, Hunter was right

Anything under 1/60 Shutter in SH (720/60P) is actually 30 with doubled frames.

That means if Sonic shot ANYT 720 footage under 1/60 shutter it's not actually 60P.

I didn't even notice it when I first had it, but it even looks like 30P on the LCD at every shutter under 1/60. As soon as you hit 1/60 it changes on the LCD.

So that explains the anomaly.

Ian-T
05-07-2009, 05:44 PM
So...when I suggested earlier to shoot with a 180 degree shutter in 60p to get that film like motion one really needs to be in 1/120? (I'm talking to drop that footage on a 24p timeline for "normal" playback). I know 1/120 is perfect for slow motion in that frame speed...but I'm not sure if we need to be at 1/60 or 1/120 for film-like "normal" motion.

I hope I didn't confuse you...lol

PappasArts
05-07-2009, 05:48 PM
Kholi,

About shutter speed, wasn't there some speculation that the shutter release cable might open the door to very long exposure's..?

Hunter Hampton
05-07-2009, 06:01 PM
So...when I suggested earlier to shoot with a 180 degree shutter in 60p to get that film like motion one really needs to be in 1/120? (I'm talking to drop that footage on a 24p timeline for "normal" playback). I know 1/120 is perfect for slow motion in that frame speed...but I'm not sure if we need to be at 1/60 or 1/120 for film-like "normal" motion.

I hope I didn't confuse you...lol

For "slow-mo" 60p, a 1/120th shutter would equal 180 degrees. If your shooting 60p and planning on dropping the unneeded frames to get 24p (realtime 24p), then 1/60th with get you the closest to a normal shutter at 24p.

Kholi
05-07-2009, 06:04 PM
Hunter is definitely on.

Can't believe I didn't see the change until now.

So if Sonics night footage is anything below 1/60 which I suspect it is it's not actual 60.

Hunter Hampton
05-07-2009, 06:05 PM
Kholi,

About shutter speed, wasn't there some speculation that the shutter release cable might open the door to very long exposure's..?

You can do 60 second exposures on this camera. Just not in video mode- if you want to shoot timelapse, you can pick up an intervelometer for the G1/GH1 very cheaply off of ebay (mine just showed up today!).

PappasArts
05-07-2009, 07:02 PM
You can do 60 second exposures on this camera. Just not in video mode- if you want to shoot timelapse, you can pick up an intervelometer for the G1/GH1 very cheaply off of ebay (mine just showed up today!).

That's awesome!

Curious, does the intervelometer as well work in video mode too, like the HVX200?

Hunter Hampton
05-07-2009, 07:06 PM
No, its only for still mode. Which is wonderful, that means you can shoot any resolution you want, even RAW. Im just shooting the 1920x1080 JPEG mode.

PappasArts
05-07-2009, 07:10 PM
No, its only for still mode. Which is wonderful, that means you can shoot any resolution you want, even RAW. Im just shooting the 1920x1080 JPEG mode.


I can just imagine how sweet those timelapse would look too!

Finster
05-07-2009, 07:30 PM
Good grief, I'm a little confused here. The fact that anything under 1/60 shutter in 720/60p = 30 ... is that a bad thing? If I shoot 1/40 shutter in 720/60p and drop it into a 24p timeline, what happens? Will it look like crap?

Regarding "slow-mo" - I would need to shoot 1/120 shutter in 720/60p and drop it into a 24p timeline in order to achieve this effect? Is that right?

This is too much to remember. I'm just going to shoot in AUTO MODE all the time! :embarasse

Hunter Hampton
05-07-2009, 07:39 PM
Its really simple- its impossible to expose 60 frames per second at anything less than 1/60th second. So when you drop the shutter past 1/60th in 60p mode, it drops the frame rate down to 30p.

You can get a "slow mo" effect when shooting 60p with anything from 1/60th to 1/4000th shutter, as long as 60 unique frames are recorded per second, you will have 2.5x "slow mo" footage on your hands- just play it back at 24fps.

Finster
05-07-2009, 07:54 PM
Thanks for the insights Hunter.

The "slow-mo" effect can be achieved using any shutter speed that's 1/60 and higher. But Ian-T wrote that 1/120 is perfect for slow motion??? So there's an ideal shutter speed (1/120), but really anything over 1/60 will work?

Also, you said "just play it back at 24fps." That's the same as saying "drop it on a 24p timeline," yes?

Last question - the "film look" is 1/48 shutter speed, right?

Man, I'm feeling like such a new-kid-on-the-block right now. I thought this 24p HD thing was going to be cake.

dcloud
05-07-2009, 08:09 PM
film look depending on frame rate:
24p must have 1/48 shutter (1/50 on the gh1)
30p must have 1/60 shutter
60p must have 1/120 shutter

Hunter Hampton
05-07-2009, 08:15 PM
There is an idea that a 1/48th degree shutter is the golden ratio for the "film look". This is all based on the popular 180 degree shutter in most film cameras (all though the last film camera I had used a 172.8 degree shutter for exposures of 1/50th at 24p) look up on your own what a film camera mirror shutter looks like and how it works.

Basically, to equal a 180 degree shutter when measuring in fractions of a second, you just multiply your frame rate by 2. So when shooting at 24fps, a 180 degree shutter would equal 1/48th. When shooting at 60fps, a 180 degree shutter would equal 1/120th. ( which is why it was recommended to use a 1/120th shutter when shooting 60p for slow motion)

To play back video shot at 60fps @ 24fps (for slow motion), you can use cinematools to reconform to 24 frames per second, or drop the footage on a 24p timeline and slow it down by 2.5x (40%). Also most editing programs will let you conform footage to another frame rate.

It gets more complicated the more you think about it. ; )

ydgmdlu
05-07-2009, 08:19 PM
Thanks for the insights Hunter.

The "slow-mo" effect can be achieved using any shutter speed that's 1/60 and higher. But Ian-T wrote that 1/120 is perfect for slow motion??? So there's an ideal shutter speed (1/120), but really anything over 1/60 will work?
Motion picture film is usually shot with a 180-degree shutter, sometimes an even larger angle. Smaller angles might be possible, but the smaller the angle, the less technically possible it becomes. A motion picture film camera uses what's called a mechanical rolling shutter. A 180-degree shutter is a semicircle. The shutter is continuously rotating as the camera is filming. When the semicircle blocks the light from hitting the film, the camera's claw advances the filmstrip to the next frame. This is why motion picture film is typically exposed at 1/48 second, when the frame rate is 24 fps. The other 1/48 second is used to advance the film. (1/48 + 1/48 = 1/24 second, the cinema frame rate.)

So basically, the time allotted to a single frame is divided between the exposure and the film advancing mechanism. When the shutter angle is larger, the light from the lens gets blocked for a longer time, decreasing the exposure time. Films are typically shot with a 180-degree shutter, which means that the time is evenly divided, even for slow motion (i.e. "overcranked") material. That's why in the film world, the "ideal" shutter speed for 60 fps is 1/120 second. That's why for slow-motion material, you should shoot at 1/120, if you want the "film look."


Also, you said "just play it back at 24fps." That's the same as saying "drop it on a 24p timeline," yes?
No. When you drop the footage onto a 24p timeline, I'm assuming that frames are dropped (36 per second) in order for it to play at real time. (This is known as "reconforming." Changing frame rates while preserving the playing time is known as "retiming.") When you "play back" 60p at 24 fps, it means that you are changing the playback frame rate within the file header so that you get slow motion.

John Caballero
05-07-2009, 08:21 PM
When you drop 60p as recommended by Kholi on 24p timeline, not for slo mo, but for normal speed 24p output what is really happening? The program takes out only 24 frames out of the 60 at random or what? I don't undrstand the process yet. Some light please!

Finster
05-07-2009, 08:24 PM
Thanks guys. My brain hurts. I'm in the middle of watching Eternal Sunshine of the Spotless Mind, so maybe that's part of the problem? :shocked:

I'll have to try and absorb all of this a little later.

holyzoo
05-07-2009, 08:30 PM
I thought this 24p HD thing was going to be cake.

Sounds like it's cake in 1080p24 mode, except for the compression falling apart. But so far, the 60p situation looks like a clusterfu**.

I'm seeing footage work well for slow motion easily in a 30p timeline. And for 24p, I'd slow conform the 60fps down to be 48fps to be the smoothest. I'm seeing stuttering by just dumping 60p into a 24p timeline.

In my examples, the MTS files are transcoding to 29.97, even though it's been overcranked, which I don't understand - Voltaic might be giving it a 29.97(30p) header even though it's 59.94(60p). So...

When I drop it straight into a 24p timeline, the motion is stuttery...
http://www.holyzoo.com/content/dslr/GH1_60p_to_24p-StraightDrop-720x405.mov

But then I first conformed the footage to 23.98fps with Cinema Tools, then brought that into my 24fps timeline. Motion is perfectly smooth:
http://www.holyzoo.com/content/dslr/GH1_60p_to_24p-Conformed-720x405.mov

Regarding getting normal speed - not slow motion - from 60p to 24p? I'm seeing that being a process full of issues.

drk3p
05-07-2009, 09:01 PM
30 min later and your links are dead?

drk3p
05-07-2009, 09:02 PM
They are working now, werid

holyzoo
05-07-2009, 09:02 PM
When you drop 60p as recommended by Kholi on 24p timeline, not for slo mo, but for normal speed 24p output what is really happening? The program takes out only 24 frames out of the 60 at random or what? I don't undrstand the process yet. Some light please!

I would also like to know how this is supposed to work. I don't see how it can logically work, other than the fact that you have 2.5x the frame rate information, so the way FCP will remove frames, it averages out to be smoother than if you dropped 30p into a 24p timeline.

However, I'm seeing under careful scrutiny that 60p to 24p is *not* just a simple case. Frame blending could help. But unless the GH1 is embedding 24p inside 60p (it's not), how can you really get a true 24p out of it? But is it close enough? And what if you want to shoot in different shutter speeds and resolve back down to normal speed?

Here's my quick test throwing HVX200 60p into a timeline (since the 60p footage from the GH1 I have isn't suitable for the kind of test I'm doing).

720p60 at 1/120 shutter speed - it's stuttery. It's close though! I tried slower shutter, but it got blurry looking. Tried faster shutter and the stutter got worse.
http://www.holyzoo.com/content/dslr/HVX200_60p-24p-720x405.mov

720p24N at 1/48 shutter speed - smooth as we all know this combo is.
http://www.holyzoo.com/content/dslr/HVX200_24p-720x405.mov

Does anyone with a GH1 care to do a similar test?

Kholi
05-07-2009, 09:15 PM
Very glad it's in the clear that the 60P from the GH-1 is probably not an accurate test, what's been uploaded I mean.

Holyzoo, your examples both look like 24P to me, personally. Just the first one with a higher shutter.

After Hunter's discovery and my own confirmation, I think a 1/60 (Tested today) and a 1/80 (tested today) may be close enough for me, especially considering the advantage of just dropping the 60 into a timeline versus having to do the pulldown conversion stuff.

AT least that's a trade-off I'm willing to take.

Looking forward to other opinions on what the motion looks like, though!

holyzoo
05-07-2009, 09:32 PM
I think a 1/60 (Tested today) and a 1/80 (tested today) may be close enough for me, at least that's a trade-off I'm willing to take.

Post an example? I'm really hoping carefully chosen shutter speed can result in smooth motion.

This was my 1/60 shutter speed test:
http://www.holyzoo.com/content/dslr/HVX200_60p-24p_onesixty-720x405.mov

Kholi
05-07-2009, 09:41 PM
Going to cut some random junk tomorrow, some 1080/24 and some 720/60.

dmoreno
05-08-2009, 12:02 AM
Converting 60 frames to 24 frames is kind of a complicated process since 60 is not a multiple of 24 (converting 60 frames to 30 is very easy because you just drop every other frame or "blend" every 2 frames into one). There are two ways to convert 60 frames to 24, none of which is perfect: dropping some frames or blending some frames.


In order to get 24fps from 60 fps by dropping frames you need to drop 3 out of every 5 frames, keeping 2 of them. This means keeping 1, dropping 2, keeping 1, dropping 1, and so on. This will result on 24 fps footage but with a somewhat awkward motion, resulting from the fact that the lapse between the kept frames is not constant (1 frame one time, 2 frames the next one). This is the way most nle's will do the conversion if "frame blending" is disabled (frame interpolation or other names might be used ).
If you're just gonna drop frames in your NLE, to achieve the film motion blur you should record using the shutter speed closest to 1/48 you can get, , that will be 1/60.
This "frame dropping" method is the least processor intensive and should require less rendering time. As I said before, this method won't
yield "perfect" motion due to irregular intervals between kept frames (though most people won't notice, specially when no fast actions are
occurring. Actually most of us are used to this "irregular cadences" from watching 24fps footage in our good old NTSC televisions that insert the 3:2 pulldown that distorts the motion a little). The other factor that might make this method look less "filmic " is the 1/60 shutter that is a little bit faster than the standard 1/48 (180 degree shutter).


The other way of converting 60 frames to 24 is using an "intelligent" processes that will convert every 2.5 frames into one by blending the information in those 2.5 frames. This will result in a better motion cadence, due to the regular separation between the resulting frames.
If frame blending or any "re-timing" process (as the one twixtor does) is gonna be used, footage should be recorded using a shutter of 1/120 in order to get a 1/48 looking motion blur. This, because the "adding" of several frames results in a frame with the added exposure time of the original frames (adding the information of 2.5 frames shot for 1/120th a second will result in a frame with a "time information" of 1/120+1/120+1/120/2 that is exactly 1/48th of second.)
Using a frame blending process should require longer rendering times. It will probably yield a smoother motion and a simulated shutter very close to 1/48 (if the footage was shot at 1/120, if shot with slower shutters as 1/60 it might result in too much motion blur and soft looking footage). If the software implementation of this blending process is not good, it might result in blurry and less sharp footage.

So, which process is better???? It depends on your taste, the software you plan to use, and the time you want to spend in processing.
In my case, I would use "frame dropping" most of the time, specially in scenes with little motion. Maybe for sports, a rolling ball, a car crossing the frame, and things like that, frame blending might result in best looking motion.

Please excuse me if my english is not that good, it's not my native tongue (hablo espaņol!)!!!

AdrianF
05-08-2009, 03:21 AM
Please excuse me if my english is not that good, it's not my native tongue (hablo espaņol!)!!!
Considering it's not your first language you did a pretty good job!
If people are going to be working with dual sound though, any sync issues with a retiming workflow will need to be tested pretty well. It might not be a problem, but I can see some potential for disaster here.

Finster
05-08-2009, 06:43 AM
A 180-degree shutter is a semicircle. The shutter is continuously rotating as the camera is filming. When the semicircle blocks the light from hitting the film, the camera's claw advances the filmstrip to the next frame. This is why motion picture film is typically exposed at 1/48 second, when the frame rate is 24 fps. The other 1/48 second is used to advance the film. (1/48 + 1/48 = 1/24 second, the cinema frame rate.)

http://upload.wikimedia.org/wikipedia/commons/a/ad/Moviecam_schematic_animation.gif

Had to visit wikipedia. I'm much more of a visual learner! :happy:

So, are you guys telling me that a film camera with a 180-degree shutter running at 24fps will always be set to 1/48??? That never changes?

I'm thinking the answer's yes. So then, all you who want to achieve that "film look" with the GH1 - you'll always have your shutter set to 1/60 (the closet you can get to 1/48)?

John Caballero
05-08-2009, 06:50 AM
If people are going to be working with dual sound though, any sync issues with a retiming workflow will need to be tested pretty well. It might not be a problem, but I can see some potential for disaster here.

Same thought here. How do any of these two precesses affect audio done with a separate recorder? Also anybody out there know how well Edius 5 and Vegas Pro work with dropping 60P on a 24P time line? Are they good at that or what? Thanks.

upshot
05-08-2009, 07:18 AM
Hunter is definitely on.

Can't believe I didn't see the change until now.

So if Sonics night footage is anything below 1/60 which I suspect it is it's not actual 60.

I noticed that yesterday inspecting his night footage. I concur that it was actually 30p with doubled frames.

SonicStates
05-08-2009, 07:36 AM
My brain hurts too...damn...I guess some of the footage I just uploaded will have some double frame action going on...going back to re-read this thread...sorry for the F-up

SonicStates
05-08-2009, 07:40 AM
You can do 60 second exposures on this camera. Just not in video mode- if you want to shoot timelapse, you can pick up an intervelometer for the G1/GH1 very cheaply off of ebay (mine just showed up today!).

Very nice!

upshot
05-08-2009, 07:49 AM
My brain hurts too...damn...I guess some of the footage I just uploaded will have some double frame action going on...going back to re-read this thread...sorry for the F-up

LOL. How could you have known?? I had to inspect the footage very closely to notice. It makes sense though. 1/30" @ 60fps just does not add up.

holyzoo
05-08-2009, 09:35 AM
LOL. How could you have known?? I had to inspect the footage very closely to notice. It makes sense though. 1/30" @ 60fps just does not add up.

Look at the first 3 clips - they aren't double framed 30fps. They are 60p with discreet frames.

vanawesome
07-22-2009, 02:52 AM
Alright guys, something is blowing my mind here. You guys are talking about 1/24, 1/60, 120... MOST of these shutter speeds are NOT available to me on my camera. I have 1/30, then 1/40/ then 1/50, then 1/60, then 1/80, then 100, then 125, then 160 and up... what the heck? I really need that 1/24 and 1/48 action. what am i doing wrong?

yabyum
07-22-2009, 03:18 AM
by 1/120 you guys mean 1/125 right???

my camera doesn't do 1/120 shutter... just 1/125. am i doing something wrong?

commanderspike
07-22-2009, 05:21 AM
I can just imagine how sweet those timelapse would look too!

I also considered shooting a timelapse in stills mode. All cameras should have interval shooting options in the menu, I mean how hard can it be!

But with the new firmware, 1/2 shutter speed in video mode will produce some very nice timelapses indeed especially in low light.

So the codec records either 24p,30p or 60p. Is that right? The shutter speed just regulates the electronic shutter - which is a virtual shutter - which allows the sensor to be exposed - but the frame rate off the chip is always gonna be one of the 3.

I am considering shooting at 1/25 in 720p mode, and overexposing. I find that an underexposed shot at ISO 100 has more banding and fixed pattern noise than a overexposed shot at ISO 1600!!

So that way I get the best possible low light performance, a shutter speed reasonably close to the native 30p mode of the sensor and the ability to overexpose even the darkest scenes, to hide banding and allow darkening in Final Cut Pro afterwards.

I better buy some ND filters for outdoor shooting then :laugh:

PS - where have all the funny smilies gone on this forum. Some were absolute classics... *violin playing*