There is a very good (and free) deinterlacing plugin for Vegas: Smart Deinterlacer from Mike Crash.
A Google search should reveal download sites and the filter settings have already been discussed on this board (it's fairly easy to use once you've got the settings right).
I've been using the filter for years and found it much much much better than the two built in deinterlacers.

However, if you are looking for top quality you may want to to look at the "Smooth Deinterlace" filter for avisynth. Unfortunately the workflow is very cumbersome so I use that filter rarely. In my mind the gain in quality hardly justifies the workflow (which has also been described in previous discussions on this board).

Martin

Thanks for the suggestions... I will look into that Vegas plugin and I've already had some good success with fldave's suggestions.

So far my best results have been from using Virtual dub, loading an Avi Synth script which is very simply:

AVISource("20061007_YoYo2A_BenT1 - Clip 071.avi")
bob

"Bob" renders each field to a frame - thereby doubling the frame rate of the original video. And it looks way better than than Vegas's "Interpolate". The yo-yo string is a nice straight line with very minimal stairstepping, compared to very obvious stairstepping using just Vegas.

Unfortunately the background comes out looking really shimmery. The action shots are great but the details in the background become annoying. Luckily we had one HDV camera and I'm hoping the HDV fields will make nice SD frames.

I tried the "Smooth Deinterlace" but it left strange artifacts, I'm guessing because the yoyo is moving very far from frame to frame. Parts of the yoyo would show through from other fields. It's good but you can see the artifacts when the footage is slowed down, which is my intention.

The Mike Crash plug in is pretty cool:

http://www.mikecrash.com/modules.php?name=Downloads&d_op=viewdownload&cid=13

The result is comparable to the AVISynth bob method, but doesn't look quite as sharp out of the box. I was ready to compromise for the convenience of not having to make 60fps intermediary files for all my slow motion. But unfortunately, when you slow the footage down, for example by setting the playback rate to .5, Vegas adds blended inbetween frames. And if you turn off resampling, it no longer processes the fields into frames. This is the same problem I've run into over and over again with Vegas and field processing.

Before you give up on the Mike Crash smooth deinterlacer, make sure you're using it right. You need to set the project properties to 29.97 fps progressive and then insert the Smooth Deinterlacer plugin either on a track or on the master effects bus. If you don't set the project properties to progressive, basically what happens is that the deinterlacer tries to deinterlace each field separately, which is pointless. I'm just mentioning this because it took me so long to figure out.

Also, the fancier resize algorythm, bicubic I believe, doesn't work properly and doesn't give as good results when the tab is checked.

When I first tried the smooth deinterlacer, I wasn't that impressed. After learning how to set it up however, I would say that the results you can get with it are as good as anything you can get with VirtualDub or AVISynth.

Thanks Laurence - One thing that's nice about the Mike Crash deinterlacer is it didn't have the yoyo bleeding through from other fields like the AviSynth Smooth Deinterlacer.

I should get hold of the HDV footage tonight and I can run another comparison.

Either way I have to render out a 59.94fps intermediary in order to do slow motion without losing the fields... which sucks majorly since 60fps HDV is going to be HUGE as Huffy or Lagarith.

One thing that'll help is to shoot with a fast shutter speed.

All cameras were locked at 1/2000th ;-)

Where the yoyo was just a blur using default settings, now each field is a crisp shot with the yoyo and string frozen in the air. These things move really freakin fast... yoyo-ing isn't what it used to be when I was a kid!

Wow,
at that shutter speed you'll probably need a heck of a lot of light too. Is it perhaps worthwhile hiring a high speed camera?
Bob.

I can only imagine what they cost, but the "Phantom" high-speed cameras from Vision Research are almost unbelievable. They have a demo clip "Car Explosion" in which you see the supersonic shock wave propagate out from the car; amazing stuff. It was shot at 7300 fps with a 95 microsecond shutter speed.
http://www.visiblesolutions.com/index.cfm?sector=htm/app&page=gallery