Not too long ago you needed very expensive cameras and equally expensive desktop software to produce a good slow-motion video. Now we can grab slow-motion capture at up to 960 frames per second from a smartphone, and that means we can shoot video that's about 32-times slower than real life. Isn't technology grand? We don't need to know how to build a smartphone that can shoot super slow-motion video or how the internal software works to use it, but it's a good idea to know a little bit about the things you can do to make it better. Or worse.
The Galaxy S9+ can shoot slow-motion video at 240 fps (frames per second) in 1080p, or 960 fps in 720p. Sony's latest, the Xperia XZ2, can shoot 960 fps video at 1080p! We expect to see a lot more companies building phones with cameras that can tackle the super slo-mo so no matter which brand you prefer you'll probably get the feature. It sounds really cool, and it can be once you get a little bit of practice in and remember a few things about when it's best to use it versus the still-impressive 240 fps slow-motion feature.
Resolution is the biggest difference on paper, and the easiest to remember because the results are right there in front of you when you play it back. Super slo-mo shoots at 960 fps, but can only do so for less than a second (0.2 seconds in the Galaxy S9+) but that translates into about 6.5 seconds when you play it back at normal speeds. While that's awesome, there are times when a 720p video just won't cut it.
Don't let 6 seconds of 720p footage ruin your video. If it will be a jarring switch, shoot at 240 fps instead.
The thing you'll be playing the video back with very likely has a very high resolution. A computer monitor, television, or even the display on your smartphone falls into this category. You have to decide if 6 seconds of 720p footage right in the middle of an FHD video is going to work. The best way to decide is by trial and error.
Take your phone and shoot some video of anything that's moving as a test. Play it back on the phone and upload it to YouTube where you can watch it on a bigger display so you get a feel for the way the switch to 720p looks when you're watching. It can work sometimes, especially if you're going to be editing the final product, but other times it isn't going to cut it and the FHD 240 fps capture will work better, even if the footage isn't quite as slow-motion.
Keeping the phone still
Slow-motion video is a bit blurry. It's difficult for even the most expensive cameras to capture high-speed video and still get a great sharp image because it's next to impossible to take enough samples to fine tune the focus. It's not too bad looking, and it can even add to the effect, but only if it's done right.
In this case, done right means the camera is held perfectly still. Especially if you're going to use the Automatic capture feature in the Galaxy S9+, where it detects motion and grabs the super slo-mo footage when it sees something moving. Keeping your camera perfectly still is important.
Even the tiniest bit of shaking in your hands can look like an earthquake when you slow it down by a factor of 32.
In fact, it's important enough to invest in a tripod or gimbal if you plan to shoot a lot of super slo-mo video. With the right equipment your phone can take some amazingly great video footage, and investing in some gear to make better use of it isn't a bad idea at all.
We really like the DJI Osmo Mobile 2 gimbal here. it can account for any small hand motions (the smallest shake goes on f-o-r-e-v-e-r when shooting at 960fps) and can be programmed to enhance your video with other effects through the mobile app. It's a handheld, but you can pick up a number of attachments that will let you place it on a flat surface on a tripod. And best of all, the $130 price is a lot cheaper than some others out there.
If you don't have a way to keep your phone still while taking slo-mo video, shoot it at 240 fps if the video needs to be stable and level.
Know your lights
Lighting is the biggest thing to consider when you're taking any photo or video. You need the right light in the right amount to properly expose whatever it is in front of the lens, and when shooting at high speeds you get another factor in the mix: pulse modulation.
We can see more things when they are slowed down. things like blinking lights.
Pulse modulation is how fluorescent lights and LED's "work". A "regular" light bulb has a filament inside of it that's superheated in a sealed glass globe. It gets so hot it emits bright light and the sealed environment keeps it from catching fire and lets it last longer. It's also a steady emission — it gets hot, puts out light, and stays in that state until you turn off the electricity and it cools down.
Fluorescent lamps are driven by a ballast that pulses high voltage through the contacts. This ionizes a small amount of metal (usually a mercury-based metal which is why you should never handle a broken fluorescent lamp) and causes it to emit a lot of UV radiation (the harmless type). A phosphor-based coating on the inside of the glass converts the UV radiation into visible spectrum radiation, which is light. Hot cathode fluorescents work a little differently and need a long arc to cause vapor in the sealed lamp to glow, but when it comes to the timing they are both the same — they turn on and off about 60 times each second.
LEDs use a driver to apply current to the leads of the lamp, and this causes electrons to move in a semiconductor inside the LED. When the right amount of current is applied, the electrons are converted into photons, which are tiny rays of light. Fluorescent lamps and LEDs don't work quite the same way, but they have one thing in common: they aren't a steady light source. LEDs can have an on/off cycle as slow as two times per second.
240 fps will make fluorescent lights and LEDs blink, but a lot less than 960 fps will. It makes a big difference.
This doesn't matter to our eyes because we can't see the darkness between pulses when they are that fast. But when you slow down your video by shooting at a very high frame rate, you see it in the end result. Sometimes, it can be so bad it ruins the footage. Shooting video under a normal fluorescent lamp at 240 fps the lamp "blinks" 7 times per second. Shooting at 960 fps it blinks a little less than 2 times per second. That's easy to see, and there's no way to edit it out.
Ideally, you want to shoot outside in the sun or using old-fashioned filament lighting. But if you can't do that and are shooting video under fluorescent lights or LEDs, shoot at 240 fps to minimize the flickering.
The most important thing to know is that it gets better with practice, and practicing is pretty fun. Shoot video of all kinds of things and have fun while you're figuring it all out!
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