How to adjust a compendium

Sir
I have purchased a 4x5 compendium. I am not too clear on how to properly adjust it. How do I prevent vignetting.
Thanks
Jerry Cunningham

You prevent vignetting the same way you normally would--look at the groundglass.

If you can't see the corners, then if you have a groundglass with cut corners you can look with the lens stopped down and see if you can see the full aperture of the lens through the cutouts. If the compendium is blocking the light path, you'll see it through the lens.

If you don't have a groundglass with cut corners, do it from the other side. Look through the lens, stopped down, with the groundglass unobstructed (i.e., without a filmholder in the camera or the darkcloth hanging over the glass), and look to see if you can see the corners of the groundglass through the aperture of the lens, and adjust the shade accordingly.

As David said, but first stop down to the taking aperture. Vignetting wide open will not affect the image as long as it is no longer present after stopping down.

Thanks very much for the help. I got it figured out.
Jerry