So i brushed the dust off of a Brevis, and wanted to play with some of my Nikon lenses...
I had always assumed the Brevis would imitate the same crop value as a 35mm camera, or at least a 35mm film camera..
I also assumed, that the ground glass would imitate the same sensor/film size of the above mentioned.

But when i put on my 28mm glass, i've only got about 8' of width at about 10' of distance. The frame was cropped beyond belief.

Once i take off the glass, and remove the Brevis, at full width, my XHA1 gets 16' at the same distance.
What gives?

Is my setup wrong, or have i been fooled into thinking that the Brevis should be giving me same crop values as a still camera?

There are a few variables but my first guess is that your expectation is to find a full sized 35mm still-image frame that you would see on a film SLR or full sensor DSLR camera like the Canon EOS 5D.

In the 35mm stills cameras, the film comes across the gate horizontally and the image frame is wider than would fit between the sprocket holes in the film.

With common 35mm motion picture film frames, the image is cast onto the film which steps through the gate in a vertical direction. The sideways space the image frame can fit into between the sprocket hole rows is smaller. Space reserved for the optical soundtrack reduce the width even furthur.

Most of the 35mm groundglass based image relay adaptors, even they they commonly mount stills 35mm lenses, for practical and technical reasons do not use as wide an image on the groundglass as a 35mm stills camera and originally were never intended to.

They were intended to faithfully emulate the look of 35mm motion picture film in perspective, field of view and depth of field, for given lens focal lengths.

Your 8ft width of frame at the subject is therefore consistent with what you would see in a motion picture camera frame. Many of the alternative groundglass adaptors including the Brevis have permitted a wider frame than the original benchmark P+S Technik Mini35 which I think had an image frame width of 22mm.

Natively your camcorder has a 1/3" (approx 8mm) sensor area and it wears a zoom lens which at its wide end confers 4.5mm focal length. In approximate 35mm motion picture camera terms, this equates to requiring a 14mm focal length lens for the same available field of view and for the stills camera frame, a lens of about 18mm focal length. I think the widest available non-distorting lens for 35mm motion pictures is 8mm, which is about 2.5mm for your camcorder's 1/3" sensor. There are other variables governed by how much of your camcorder's sensor area is comprised of active pixels.