I found the answer to my question and it is the camera ....
I found this on some other forum:
Slow Motion Quality
Most people want to create slow motion like they see on sports programs. Unfortunately, that quality cannot be duplicated because they use cameras that take far more than 30 frames per second. To create slow motion when Vegas only has 30 fps to start with (or 25 fps for PAL), it must create new frames of video to fill in the time between each original frame of video. Vegas does this by blending the adjacent frames. The result gives the illusion of fairly smooth slow motion, although, because the intermediate frames are the combination of adjacent frames, they are somewhat fuzzy. Thus, you can get smooth, but slightly blurry video.
If you want crystal sharp slow motion, you can right-click on the video event that has been slowed down, select “Properties,” and then click on the “Disable Resample” setting. This will tell Vegas to simply play back the original frames, but at a much slower rate. The effect is identical to what you get when you slow down a movie projector. As you make the playback slower and slower, you begin to see just a series of still images, one after another. Each frame is exactly as sharp as the original, but it gets very “jerky” as the motion is slowed.
There has been much discussion of other settings, such as supersampling, best mode rendering, and setting project properties to “interpolate frames” instead of “blend fields.” These don’t make the motion look any smoother. If you find that your slow motion exhibits flicker, you can enabling the Video Bus track (in the View menu), adding a Motion Blur envelope, and setting it to somewhere between 2-4. You can also try right-clicking on the event, select Properties, and click on reduce interlace flicker. Don’t do either of these things if you don’t have to, because they both can slightly degrade the video’s crispness, and Motion Blur substantially increases rendering time.
So there you go, if you are having trouble getting good quality slow motion, then perhaps you should consider what is happen at the source of your capture.