Shutter Interval for Sports Shooting

[Jon Fairhurst]

It's general knowledge that cinema is shot at (or around) 24 fps with a default shutter angle of 180 degrees, or 50%, which is 1/48 sec. For slow motion, maintain 180 degrees regardless of the frame rate, conform to 24 fps, and the motion looks "normal".

But what about 60 fps sports on TV? I've heard people talk about a fully open shutter (360 degrees), but I'd like to know if this is common practice.

There are a few things to consider.

Like older cameras vs. new cameras. Maybe they used 360 degrees in the old days to reduce noise, especially during night games. Modern cameras are more sensitive and sports lenses have improved, so maybe we've moved to 180 degrees for sports.

And then there's interlace... Maybe a longer shutter reduces flicker for 480i and 1080i. But then you have ABC, ESPN, and FOX shooting 720p...

We also need to consider slow motion. We want crisper images for slo-mo, but if you drop frames to give real-time 60 fps video, one could get strobing.

Given all this, what is standard practice today?

[Bruce Watson]

Originally Posted by Jon Fairhurst

It's general knowledge that cinema is shot at (or around) 24 fps with a default shutter angle of 180 degrees, or 50%, which is 1/48 sec. For slow motion, maintain 180 degrees regardless of the frame rate...

What makes you think that? The "180 degree rule" is about 24 fps (and it implies global shutter). The faster your frame rate, the less meaning the 180 degrees rule has. When you get up to 240 fps, it has no meaning at all. Just about everything shot at these high frame rates use 360 degree shutter. That is, shutter speed = frame rate.

You should play with still photography some. You get hardly any motion blur with 1/250th second shutter speeds. Very little at 1/125th. Make a few snaps, take them into photoshop, and really look at them. What do you see?

[Seth Bloombaum]

Please excuse my ignorance, be gentle with me... but I'm interested in this as it affects some upcoming shoots. These two posts have piqued my curiousity!

Originally Posted by Jon Fairhurst

It's general knowledge that cinema is shot at (or around) 24 fps with a default shutter angle of 180 degrees, or 50%, which is 1/48 sec. For slow motion, maintain 180 degrees regardless of the frame rate, conform to 24 fps, and the motion looks "normal".

That's my understanding of the conventions as well. That is, "normal" motion blur is an aesthetic value that we've all been trained to. The equivalent of apx. 180-deg shutter (shutter speed of half the frame rate) produces "normal" motion blur.

Originally Posted by Jon Fairhurst

But what about 60 fps sports on TV? I've heard people talk about a fully open shutter (360 degrees), but I'd like to know if this is common practice.

There are a few things to consider.

Like older cameras vs. new cameras. Maybe they used 360 degrees in the old days to reduce noise, especially during night games. Modern cameras are more sensitive and sports lenses have improved, so maybe we've moved to 180 degrees for sports.

And then there's interlace... Maybe a longer shutter reduces flicker for 480i and 1080i. But then you have ABC, ESPN, and FOX shooting 720p...

AFAIK all 60i shot to broadcast standard was *always* 1/60th shutter speed. Which is not a 360 shutter, but 180-deg shutter based on an apx. 30fps frame rate. Back in the days of phosphors and big glass picture tubes that shot electrons at them the latency of the glowing phosphors meant that one never perceived an individual field, but only frames.

I never had access to the real network sports slomo gear back in the day, but a lot of regional/local slomo was done with 60i material by patiently spinning the jog dial on a Betacam deck equipped with a TBC that assembled non-jaggy frames out of the interlaced recording. What we'd consider "real" slowmo was only shot on overcranked film cameras. NFL Films was huge in covering football in film at the same time it was broadcast SD60i, and yes they did a *lot* of overcranking.

Originally Posted by Bruce Watson

What makes you think that? The "180 degree rule" is about 24 fps (and it implies global shutter).

Well, that's really splitting hairs IMO. Yes, 24fps film is where the aesthetic value started, but all the wannabe filmmakers have won the terminology battles, and we talk about 180-deg shutter for devices that don't have spinning disk shutters all the time. But at 30fps we conventionally use a 1/60th shutter speed for "normal" motion blur whether at 30p or 60i.

Originally Posted by Bruce Watson

The faster your frame rate, the less meaning the 180 degrees rule has. When you get up to 240 fps, it has no meaning at all. Just about everything shot at these high frame rates use 360 degree shutter. That is, shutter speed = frame rate.

240fps, playing back at 30fps implies 1/8th slomo. That is, we're seeing continuous video, not frame-by-frame. I guess the question I have is "what shutter speed produces 'normal' motion blur" in this specific situation. Bruce seems to be saying that 1/240th is most commonly used - why not 1/480th? Or, even, 1/120th? Anybody seen reference testing done on this of common subjects like people walking, running, talking, jumping?

Does the common practice produce a normal motion blur aesthetic, or is a new aesthetic coming with these now readily available slomo cams?

[Jon Fairhurst]

Great point about 1/60 being 180 degrees for 60i if you consider frame rate rather than field rate.

Still, I'm interested to know the standard practice today. When watching a major sporting event, is 720p60 shot at 1/120 or 1/60? Is 1080i shot at 1/60 (apparently so)? And what is the current practice for standard slow motion sports cams? Are 120 fps cams shooting at 1/120 to avoid flicker from lighting? I assume that faster, super-slow-mo cams are shooting 360 degrees just to get as much light as possible. And yes, we see flicker from source lights in the really slow stuff.

Let's consider the 720p standard slo-mo case. If they shoot 1/120 at 120 fps (360 degrees), one can drop every other frame to get real time 60 fps at 1/120 (180 degrees). Or you can playback at half speed to get slow motion with 360 degrees. By shooting at 1/120, one avoids flicker in both cases (in 60 Hz countries, of course.)

In Europe, that would translate to 100 fps and 1/100. Dropping every other frame yields 50 fps at 1/100 (180 degrees) and playing half speed yields 50 fps slo-mo at 360 degrees, once again avoiding flicker in both slow and normal playback.

Any sports shooters out there who can confirm it?

[Bruce Watson]

Originally Posted by Seth Bloombaum

240fps, playing back at 30fps implies 1/8th slomo. That is, we're seeing continuous video, not frame-by-frame. I guess the question I have is "what shutter speed produces 'normal' motion blur" in this specific situation.

This is why I said to make some stills at 1/250 second shutter. Look at them in photoshop. Do you see any motion blur? Why guess when it's so easy to know?

Originally Posted by Seth Bloombaum

Bruce seems to be saying that 1/240th is most commonly used - why not 1/480th?

Lack of light. Going up a stop means adding a stop more light. This can get big and expensive in a hurry.

Originally Posted by Seth Bloombaum

Or, even, 1/120th?

You can't have a shutter speed below the frame rate in normal operations. An exposure of 1/120 second with a 240 fps frame rate would expose two frames. The result would look essentially the same as no shutter at all, which is how 360 degree shutter is implemented on some old film cameras IIRC.

Originally Posted by Seth Bloombaum

Anybody seen reference testing done on this of common subjects like people walking, running, talking, jumping?

Easy enough experiment for you to run. See what you think.

[Bruce Watson]

Originally Posted by Jon Fairhurst

And what is the current practice for standard slow motion sports cams? Are 120 fps cams shooting at 1/120 to avoid flicker from lighting?

Something like this.

[Seth Bloombaum]

Originally Posted by Bruce Watson

This is why I said to make some stills at 1/250 second shutter. Look at them in photoshop. Do you see any motion blur? Why guess when it's so easy to know?

Because my viewers don't still frame the video to evaluate motion blur?

I'm well aware of what motion blur is, where it comes from, and in still photography, how to use it to indicate speed. Hummingbirds are a particular interest, man those wings go fast.

It seems to me that the "normality" of this or that amount of blur must be evaluated under typical viewing circumstances of one's audience. IMO the interesting discussion of motion blur in video is the aesthetics that lead to beauty and credibility, moreso than the engineering and technology. Perception is truth in this.

Originally Posted by Bruce Watson

Easy enough experiment for you to run. See what you think.

Well, one of these days I'll have one of the overcrankable cams in the shop, and I will. Until then I'm in the hunt for reference footage. I do agree with your implication that ultimately I need to decide on a look that I think suits my subject and how I want to portray it... In the mean time I'd like to train my eye in motion blur effects, having rested on the standard settings for such a very long time.

[Jon Fairhurst]

Yeah, for normal motion and normal lenses, 1/250 stops motion. Shoot wide across the Grand Canyon and 1/15 might be adequate, even handheld. Hummingbirds and handheld 600mm lenses with 2x extenders in the hand are another story. I have yet to try to photograph a speeding bullet...

FWIW, BBC reported that 300 fps was needed for crisp, realistic sports action for 4K in real time. NHK upped the ante by claiming 600 fps (possibly for 8K) is needed for a fully realistic experience.

But enough with theory. What is the current practice? Surely somebody at DVInfo knows what settings are used on sporting events.

[Jim Andrada]

Well if you want to handhold a shot of a speeding bullet with a 600mm lens you stand directly in front of the gun so you don't have to pan to follow the bullet, just hold steady.

[Jon Fairhurst]

Regarding the bullet shot...

YouTube (Short URL)

My question remains on current shutter practice for live sports TV, including 1080i, 720p, and basic slo-mo cams.

[Jim Andrada]

Hi Jon

Thanks for the links

Wish I could help re your original question but the last time I had anything to do with high speed cameras we were filming the burn of individual propellant grains for 16 inch naval rifles at around six million fps.

[Jon Fairhurst]

Six million fps!?! Add a rotating mechanical shutter and you wouldn't need to stabilize the camera due to the flywheel effect! At least when you film propellant grains, they provide their own light source...