| 1 | Duplicate your 4:3 Sequence. |
| 2 | In the duplicate Sequence, apply the Widescreen filter with a 1.78:1 (same as 16:9) ratio to all clips. (You can skip this if you want - it'll only help you zoom the frame in step 5 and it will probably increase rendering time) |
| 3 | Make a new Sequence, and make sure "Anamorphic 16:9" is checked. |
| 4 | Drop the duplicated 4:3 sequence in the new 16:9 sequence. |
| 5 | Zoom the [matted] 4:3 frame to fill the 16:9 picture area (you can just drag the handles in the corners).
[If you have the time and want to get advanced, you'll do this on individual clips to crop out only unwanted stuff - not just zoom in straight on the centre.] |
| 6 | Render out the sequence before printing to video. |
Remember, Final Cut will seem to "letterbox" the 16:9 sequence in your Final Cut Canvas (the window where you view your edited stuff).
This happens if the Canvas is in the shape of 4:3 (which it often is in the standard window layouts).
But the picture really is anamorphic - you can test this by hooking up a 4:3 video monitor (the picture is horisontally squeezed) or by printing to video and displaying the picture on a 16:9 set.