Shutter Speed, Frame Rate, Smooth Slow Motion

[Pete Cofrancesco]

Whats the optimal settings for slow motion? I'm thinking of is doing an action scene. Someone throws a punch and I slow it down in post then speed it back up. Am I right in thinking that the camera is only capable of capturing 60 frames a second and increasing the shutter speed won't add any more frames? I plan to use use a plugin in FCP to create smoother slow motion but wanted to know if there is anything I should be doing while shooting. How do the pros do it besides using a special slow motion film camera? There is an example on Twixtor site that shows what I'd like to achieve.

http://www.revisionfx.com/products/twixtor/

[Boyd Ostroff]

Regardless of the shutter speed, the camera always captures 30 frames each second (or 25 if you set the Z1 for 50i), but the frames are divided into two fields that consist of the odd and even scan lines. Personally I would leave the shutter set to the default, which is 1/60 sec. But I would read all the documentation for whatever software plug-in you're planning to use. I suspect you will find some advice there about how to get the best results.

[Aric Mannion]

Originally Posted by Pete Cofran

Whats the optimal settings for slow motion? I'm thinking of is doing an action scene. Someone throws a punch and I slow it down in post then speed it back up. Am I right in thinking that the camera is only capable of capturing 60 frames a second and increasing the shutter speed won't add any more frames? I plan to use use a plugin in FCP to create smoother slow motion but wanted to know if there is anything I should be doing while shooting. How do the pros do it besides using a special slow motion film camera? There is an example on Twixtor site that shows what I'd like to achieve.

http://www.revisionfx.com/products/twixtor/

I'm pretty sure the pros would only use a slow mo camera, as it doesn't really make sense to do it any other way. But I did see a pro documentary where they slowed some shots down and it was very stuttery. They either shot it in 24p or maybe it was a 25fps cam instead of 30. That had an interesting effect actually, that I don't think they planned on.
If you have after effects there is a time warp effect that looks like that twixtor video. I don't know the best shutter speed to shoot with, it would be interesting to know if a higher speed actually makes a difference, as opposed to 60.

[Martin Pauly]

There are tools that can slow down footage reasonably well, such as Apple's Shake. Granted, it is no replacement for a camera that can be overcranked, but if you can't get one of those, then these software tools offer better results than simply duplicating or blending frames.

My rule of thumb is that I use a faster shutter when I shoot a scene that will be slowed down. For example, assuming I use 1/60sec for normal speed and I plan to slow it down to 50% of the speed, I'd set the shutter to 1/120sec for the shoot - same speed you'd use if you actually were overcranking the camera. That seems to produce usable results.

- Martin

[John Cash]

If you have FCP studio2 choose the speed you want the clip to run at and then render it. Now send it to motion. You need to pull up the inspector window.

Going by memory here because Im no where near the computer but I think it the "timing" setting. Change it to "optical flow" . This will take FOREVER even with a fast machine so do it at the end of the day and come back tomorrow.

It wont replace overcrank or undercrank but it will smooth it out a bit.

Warning though, if the clip you want to slow down is long then you need to cut out what you want to slow down and copy it and then apply optical flow . Otherwise it will apply it to the whole clip and that can take a couple of days

[Steven White]

If I was interested in slowing down footage, I'd be very careful about selecting the shutter. For cinematic effect, a "180 degree" shutter is typical, which is 1/2 the frame duration.

The best slow motion is achieved by converting fields to frames. This means shooting 1080i60 will allow you to achieve 2x slow motion in a 29.97p video, and 2.5x slow motion in 23.976p video. In the fields->frames approach, the "180 degree" shutter is 1/120.

If however, you choose a different slo-mo factor (4x for example), you will want to decrease the shutter to 1/240. In order to get smooth slow motion though, you will need some kind of motion estimation. You can use frame blending as well, but it won't be as smooth.

Do NOT shoot with a 1/60 shutter. When you slow your footage down, everything will look like it has motion blur, but nothing will be moving. Using a high shutter speed is far more desirable.

-Steve

[Ron Evans]

Originally Posted by Boyd Ostroff

Regardless of the shutter speed, the camera always captures 30 frames each second (or 25 if you set the Z1 for 50i), but the frames are divided into two fields that consist of the odd and even scan lines. Personally I would leave the shutter set to the default, which is 1/60 sec. But I would read all the documentation for whatever software plug-in you're planning to use. I suspect you will find some advice there about how to get the best results.

Camera actually shoots at 60 frames a second( hence the need for a shutter of 1/60) but only records 60 fields( half the vertical resolution). That is field 1 from frame 1 and then field 2 from frame 2 etc. Output is 60 fields a second ( interlaced). In my mind it is incorrectly called 30fps because two fields are required to make a full frame. Unfortunately just adding two consecutive fields from an interlace camera will not give you two fields from the same frame!!! Sensible deinterlacing creates 60 frames per second progressive to capture the image that was recorded not the potentially stuttering 30p output.
Interlace television was designed as a system exploiting the phosphor characteristics of a CRT display that to the viewer would perceive a full 60 frames per second image. The deinterlacing required by "modern" flat panel displays can make a complete mess of this conversion.
To get to the question. Yes pros use a special camera that can record at higher frames rates. IF you have a consumer cam leave at 60i and shutter at 1/60 and let the software sort it out!!!
Ron Evans

[Martin Pauly]

Originally Posted by Ron Evans

IF you have a consumer cam leave at 60i and shutter at 1/60 and let the software sort it out!!!

Ron,

That doesn't match my experience. Leaving the shutter at 1/60 results in motion blur being recorded that, to my knowledge, software is not capable of removing or reducing later. Not sure if the analogy is correct, but to me that would be similar to relying on software to remove reverb from an audio recording, which the experts agree is also not possible. Once it's blurry, the original crisp information is lost and cannot be recomputed. That doesn't mean that blur (or reverb) is a bad thing; it's just that the amount has to be just right to make it look/sound right. And with blur and reverb alike, it's easy to add more later, so if in doubt, I always err on the side of recording less rather than too much.

The best slomo results that I've achieved (using the Z1 and Apple Shake) have been when the shutter speed was adjusted for the intended playback speed of the video. In other words, the actual shutter speed at the time of recording divided by the speed factor (e.g., 0.5 for half the speed) should be 1/60, such that the amount of motion blur visible at playback time is the same as what an appropriately overcranked camera would have recorded. Then the amount of blur looks right for the playback speed.

- Martin

[Steven White]

Martin, you are exactly right, and your reverb analysis holds. I can confirm this both as a visual effects hobbyist and as someone with significant scientific experience in image processing.

[Ron Evans]

Originally Posted by Martin Pauly

Ron,

That doesn't match my experience. Leaving the shutter at 1/60 results in motion blur being recorded that, to my knowledge, software is not capable of removing or reducing later. Not sure if the analogy is correct, but to me that would be similar to relying on software to remove reverb from an audio recording, which the experts agree is also not possible. Once it's blurry, the original crisp information is lost and cannot be recomputed. That doesn't mean that blur (or reverb) is a bad thing; it's just that the amount has to be just right to make it look/sound right. And with blur and reverb alike, it's easy to add more later, so if in doubt, I always err on the side of recording less rather than too much.

The best slomo results that I've achieved (using the Z1 and Apple Shake) have been when the shutter speed was adjusted for the intended playback speed of the video. In other words, the actual shutter speed at the time of recording divided by the speed factor (e.g., 0.5 for half the speed) should be 1/60, such that the amount of motion blur visible at playback time is the same as what an appropriately overcranked camera would have recorded. Then the amount of blur looks right for the playback speed.

- Martin

Have to agree with your analysis.

Ron Evans

[Pavel Tomanec]

Hello,

Would people please shed a little light on the benefits shooting footage for slow mo in progressive (frame mode) as opposed to interlaced mode?

In this query I would like to leave out the shutter speed... suppose you know what is your subject, what shutter speed you'll need and how many times you'd need to slow down (re-time) the footage.

Many thanks.

Regards,
Pavel

[Boyd Ostroff]

Originally Posted by Pavel Tomanec

Would people please shed a little light on the benefits shooting footage for slow mo in progressive (frame mode) as opposed to interlaced mode?

Remember, this is the forum for the Sony FX1 and Z1. These are interlaced cameras which don't shoot true progressive footage. They do offer CineFrame mode, but I doubt that it would make much sense for slow motion. For info on CineFrame, see Adam Wilt's article here: AJW's HDV Info: Cineframe modes explained

[Pavel Tomanec]

Originally Posted by Boyd Ostroff

Remember, this is the forum for the Sony FX1 and Z1. These are interlaced cameras which don't shoot true progressive footage. They do offer CineFrame mode, but I doubt that it would make much sense for slow motion. For info on CineFrame, see Adam Wilt's article here: AJW's HDV Info: Cineframe modes explained

Thank you. Apologies for posting in the wrong section. Would be possible move the query to appropriate thread or start new discussion?

Btw the article you are referring is very informative, I wonder whether the has been something similar done for the 24/25f mode on the Canon XH A1.

Thanks again.
Pavel

[Boyd Ostroff]

Originally Posted by Pavel Tomanec

Would be possible move the query to appropriate thread or start new discussion?

Hi Pavel. At this point, I think the easiest approach would be for you to start a new thread on progressive vs interlaced slow motion in either our general HD acquisition forum (General HD (720 / 1080) Acquisition - The Digital Video Information Network) or else the forum of whatever specific camera you're interested in.

[Dylan Pank]

Originally Posted by Pavel Tomanec

Hello,

Would people please shed a little light on the benefits shooting footage for slow mo in progressive (frame mode) as opposed to interlaced mode?

In this query I would like to leave out the shutter speed... suppose you know what is your subject, what shutter speed you'll need and how many times you'd need to slow down (re-time) the footage.

Many thanks.

Regards,
Pavel

Unless you want a step-frame look (used in the opening credits of Reservoir Dogs) where the frame rate obviously stutters, there are no benefits to shooting progressive, unless your camera (like the EX1 or the HVX100) can natively shoot higher frame rates.

If you're talking about the Canon XH A1, then shoot interlace at 50i and slow down using something like the Jes Deinterlacer (if you have a Mac). There's a good demo movie on the site that clearly shows the difference, the iMovie slow mo example is what you'd get if you slowed down progressive footage.

You can slow it down exactly 50% of the original speed. Any faster and the slow mow might look a bit uneven, any slower and you'll start to see the stutter.