In the work you/I/we do, we do 2 processes:

1] We capture in camera using the settings OF that camera.

2] We render in software using the settings OF that project/render template

And for the purposes of this discussion - Interlace<>Progressive - these 2 processes are NOT physically linked - period!

One is for onsite/studio/air balloon/on horse-back/on-motorcycle/on rollerskates . .. whatever . . . And the other process attempts to USE this footage to the best it can. And THEN we render.

Now, we can make profound directorial decisions to do with content at the point of capture ie: movement needing to be slowmo-ed; optical filters; DoF (depth of field), lighting the set; focus AND more crucially here - about interlace and so on - about HOW many frames and HOW they are collected - Either Progressive ( progressively collect One complete frame after the other) OR Interlaced (each frame separated into 2 fields and these collected as an interlace format). This is a crucial decision to make. And yes, some cameras have the ability to chose between Interlace and Progressive.

However WHAT we do in camera sometimes CAN be changed in software( that is "post"). And maybe go from Interlace TO Progressive.

And guess what? Vegas, IMO, is the KING/QUEEN of multi format rendering/editing. In the trade Vegas is well known as being "Format Agnostic" - meaning, it don't really care WHAT you throw at it - it will deal with it and WITHOUT the need for interim rendering to a useful format.

So, what we capture in - me: PAL 50 Interlaced - goes straight into a Vegas project that I've set up to accept PAL 50i - and off I go. Now, there is nothing, NOTHING to stop me mixing this up with some American NTSC; a dab of MPEG; a smidgen of JPEG or a dash of Microsoft WMV. . . or whatever . . as long AS my project settings are set to the PAL format then that is what the final project output WILL be. However, and at the point of render I can be completely dorkish & obdurate and then decide to render to a NON-project format. Meaning, it was PAL 50i and now I want to produce an NTSC. So ALL my formats get smashed into NTSC. Now I don't do this - but I could. VEGAS allows for this. Personally, my "simple" workflow is to deliver to an PAL DV-AVI and make a final render-out/decision FROM that AVI.

And yes, this CAN be confusing - I hope I haven't added to more of your confusion - It most certainly was NOT my intention.

Grazie