Hi, I am knowing my LS300, and I want to practice the 120fps option. How do I do to make this shooting convert it in slow motion? I edit in FCPX. Thanks to all.

Choose "Automatic Speed" in the Re-Time menu.

Here is the Apple support page: https://support.apple.com/kb/PH12643?locale=en_US&viewlocale=en_US

Does the camera process the Slow Motion in camera or does it have to be done in post?

When you open the files in Quicktime, they play in slowmotion. I edit in Premiere, but if you put them into a 24/25/30p timeline, the slowmo files will automatically be slow too.

The camera films at the frame rate you choose. Your editing program will generally treat the footage by length, not frame rate, so a 120 fps clip will normally drop into a 24 fps timeline and the program will drop four frames for every frame kept to keep the time length the same. However if you want slow motion you have to ask the program to treat the footage differently.

I'm not sure of the exact question being asked, so I'll offer some general thoughts on slo-mo, I use FCPX too, but stress I'm no expert and always learning about this stuff.

To shoot in slo-mo, select "high-speed" under record settings. One thing to keep in mind, the VSM crops the sensor to 46% on this setting so the field of view is smaller, but the slo-mo looks good.

When I import the footage into FCPX, if I drop it into a 24p or 60p timeline it's still in slo-mo. If I want to make it back to normal speed I select the 'transform timer Fast' and speed it up (2x/4x) depending on the frame rate and it plays back regular speed.

The part I'm still figuring out is how you can restore the audio in FCPX. When the video plays at normal speed, the audio is faster but still garbled like slo-mo. I don't know if it just records that way.

Thanks to all, I put on practice your advice and effectively, I shot a falling water stream at 120fps 24p and it plays in slow motion when open it in Quicktime; then I made shot of a beer pouring into a transparent glass at 120fps/60p and shows a good slow and appetite detail in the white bubbles of spume; additional I imported this video into the FCP X timeline in a project setting 1920x1080/24p and it looks a good slow motion, and then I applied the retime slow option at 20% and looks better yet!

Did a little bit of Slow Mo at the boxing rink today. Yes it does crop in quite a bit. I had a 35mm prime and it was tough but I managed. I hope to show a little bit of to you guys here soon.

Here a little test footage. There is one slow motion clip in this sequence. I mentioned I would post one.

Clarissa Shields The Truth - YouTube