Slow motion golf swing video: fps is only half

Two dials, and your phone shows you one

About 8xHow much shorter that study's shutter was than its own frame interval

Frame rate answers how often the sensor takes a picture. Shutter speed answers how long it stays open each time. RED Digital Cinema calls shutter angle a way of stating the second relative to the first, and puts the ceiling at 360 degrees, where the exposure lasts exactly as long as the frame. At 24 fps a 180-degree shutter lands near 1/48 second. Below that ceiling, light chooses.

The golf literature shows both being picked. The Scientific Reports study that tested three low-cost video packages on twelve golfers mounted a camera 1 m high and 4 m away and set it, in its own words, to record at 1/2000 shutter speed and 240 Hz. Each frame lasted 1/240 second; the shutter was open for an eighth of that. A phone gives you the first number and hides the second.

What the clubhead does between frames, and inside one

About 8 inchesClubhead travel during one 1/240 s exposure, 115 mph driver

TrackMan puts PGA Tour driver club speed at 115 mph, about 169 feet per second. Between one frame and the next at 60 fps the head crosses roughly 34 inches; at 240 fps, about eight. That shrinking gap is what a higher rate genuinely buys, and it decides whether a frame exists anywhere near the position you wanted to look at.

The smear is a different sum: multiply the same 169 feet per second by the exposure rather than by the interval. At 1/2000 second the head travels about an inch while the shutter is open. At 1/1000, two inches. At 1/240, the longest exposure a 240 fps clip can have, about eight inches, the whole distance it covered between frames. Too few frames and the position was never recorded; too long an exposure and it was recorded as a streak. Raising the rate treats only the first.

Why the dark bay loses to the bright car park

2-1,000 luxIndoor levels in the light-sensor study, against 20,000-100,000 lux in sun

A phone's aperture is fixed, so once the frame rate is set the camera trades two things: how long it exposes and how hard it amplifies. Exposure cannot run past the frame interval, so 240 fps caps it at 1/240 second before anything else is decided.

Then the light. The wearable light-sensor study calibrated its devices across indoor levels of 2 to 1,000 lux and outdoor conditions from 5,000 lux under overcast up to 100,000 in sun. Its brightest indoor setting and its brightest outdoor one sit two orders of magnitude apart. Indoors the camera runs out of exposure time and starts amplifying; amplification is noise, and noise reduction softens edges.

Outdoors at 60 fps a full 1/60 second is available and most of it is unnecessary. Should the light let the camera settle on 1/1000, that clubhead smears two inches rather than eight. The filming guide's rule that a bright 60 fps clip beats a dim 240 fps one has this arithmetic underneath it.

What a smear does to an angle you are measuring

Pose tracking has to place a single point on a joint. A sharp frame offers a wrist with an edge on it; a blurred frame offers a band, and the point settles somewhere inside it. An angle is drawn from two such points, so both ends of the line wander.

Short segments suffer most. Take a limb measuring 100 pixels and suppose each end can land eight pixels either side of true: the line through them swings several degrees with nothing in the swing having changed. Resolution will not rescue you, because a smear covers the same fraction of a 4K frame as of a 1080p one. Extra pixels help with the other error, the slop in placing a point on an edge.

Direction is the awkward part. Blur adds no constant you could subtract; it adds scatter, and scatter is what makes one clip disagree with the next. Which numbers a phone can honestly produce belongs to the guide on what a phone can measure. No published study puts a figure on the joint-angle error motion blur costs in a golf swing, so treat frame-rate rules of thumb as reasoning from physics.

The settings that matter on an iPhone and a Pixel

Apple's iPhone 17 Pro specification reads slo-mo at 1080p up to 240 fps and 4K Dolby Vision up to 120, with ordinary 4K video at 24, 25, 30, 60, 100 or 120 fps. Choosing 240 costs the 4K frame as well as capping exposure. Google's camera help puts Pixel rate under a Frames/sec toggle, tops 4K out at 60 fps, and tips 1/8x for the fastest subjects.

Neither stock app gives you the shutter. Blackmagic Camera, free on both stores, does: frame rate, shutter angle, white balance and ISO in one panel, 24 fps up to 120 depending on the device, and it says outright that shutter speed is how you control the amount of motion blur in an image.

The order that falls out of this is light, then rate, then resolution. Where to stand and how to frame the club belong to the filming guide. Pebble Swing reads joint angles and the backswing-to-downswing tempo ratio out of whatever frames it is handed, which is why the exposure on those frames earns a minute of setup.