I shoot exclusively in DVCPRO-HD 720p24 and edit it natively. When making the files for DVD authoring, in Compressor, I select “SD (Automatic)” and let it go to town. I end up with better looking images than when I used to shoot/edit native SD all the way through. Once downconverted in Compressor (and Compressor does a super great job for my work) to SD, it’s not full HD quality, no, BUT it is better quality than if I had shot it in SD.
Just remember to shoot your HD master with the SD 4:3 size in mind. In other words, when you go to full screen SD, the left and right sides of the image will be cut out. Plan for that when framing up shots, and you’re good to go!
I moved from the DVX100 to the HVX200, did a LOT of testing of things before I decided that the straight forward method I’ve presented is pretty much the best method. Don’t worry, you’ll end up with better video images than had you shot with SD to begin with.
Oh, one last note, the book “Compressor Quick-Reference Guide” has some fantastic info in it on this conversion process, and will give you more details about doing the convertion in Compressor than I can give here. And when you can get it for around $23 on-line, I think it’s a MUST-HAVE for all FCP users.
And finally, I have done both of these, got same results either way, and great results at that. A) Drop HD 16:9 Sequence into an SD 4:3 Sequence, size and line it up for full screen (not letterbox), Render, Export. B) Use the Frame controls and such in Compressor to do the sizing (again, the “Compressor Quick-Start Guide” will be needed to learn the details of doing it). Either way, I get better images then shooting/editing native SD.