One thing I was struggling with for a bit, was why 60i would be smoother then 30p. For each of these modes, you have 30 full frames of video per second. I recorded a clip in all 3 modes (60i, PF30 and PF24) in attempts to understand the clips, as well as figure out how to get the footage into EDIUS, the software I use for editing.
I shot all the clips in Tv mode at 1/60th of a second on a Canon HG21.
60i does have that very smooth look to it that is different from PF30 so there must be something different. So "Why does 60i look smoother then 30p?"
60i actually is shooting 60 frames a second at half the vertical resolution. PF30 (30p) is shooting 30 full frames a second. PF24 (24p) is only shoooting 24 full frames a second.
On my camera, as well as many others, each all of these videos are encoded into a 60i stream. For 60i, nothing needs to be done. For PF30, each frame is simply divided into two (odd /even fields, whatever). For PF24, the telecine process is applied.
To reverse the effects on the clip the following needs to be done
60i - nothing. There is no real reversal here. You can apply de-interlacing algorithms that would either give you 30p and do averaging/blending or you could also get 60p, but again you would be interpolating/averaging.
30p - simply separate the fields back out to get progressive content
24p - you must actually apply inverse telecine processing.
I was able to get all apply these processes in AviSynth but have not yet figured out a good way to apply them to EDIUS.
In general, you want to shoot your video such that the shutter speed is 2x or more then the frame rate of the video. This is part of what gives video that "film" look. There is a good video/article out there that explains why this is necessary but I cannot locate it. I will update this post when I find it.
This means for
60i you should shoot 1/120th or faster, though it really doesn't matter since 60i is going to give far smoother motion and likely prevent the film look
30p should shoot 1/60th or faster
24p should shoot 1/48th or faster