50i to 50p

[Andrew Yoole]

Your best method for creating good quality slow-mo is to use a tool built for the job, rather than screwing with the footage before you slow-mo it. AE 7 includes Timewarp, otherwise a third party option is Re:Vision Fx’s Twixtor.

https://www.revisionfx.com/rstwixtor.htm

Both these tools track motion vectors in footage to intelligently build new frames in between existing ones. So long as your footage is interpreted correctly, there is no benefit to deinterlacing the footage.