Because of the rapidly expanding cone, one does have to get the eye close to the knife. For comfort and safety one might make the knife edge on film by exposing a half of the frame to a focused white image etc.. Or use a thin tape on clear plastic or glass.

You might experiment with an eyepiece or as Bob says a video camera. The problem with the video camera may be that the barrel of the lense might not let one get close enough to see the fully illuminated image on a fast f:1.1 but if it is a cheap lens it probably could be machined down.

I would like to hear what you finally figure out.

Good Luck,
-Rick