Vison-FX's Twixtor is a one of the best ways to create really smooth slow motion. It is recommended that you shoot at around 60fps at a minimum for Twixtor to be able to add extra frames To download a trial click here.
Twixtor is a great way adding extra frames to create really smooth slow motion. But it is expensive and if you do not have it then you can at least use Final Cut Pro and Motion as explained in the following tutorial from Crumplepot.
Another super cheap way is to take continuous photo bursts and slightly change the movement.
Its shot in real time but the movement is slow and slow down to look like 1000fps. Fantastic stuff though, I wouldn't be able to tell.
What not film some slow-mo on your dolly slider and get some awesome video footage. If you do please send us a link to your work - email@example.com
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