Argus Auxiliary finders...
Just picked-up an Argus - Geiss Sandmar Zoom-View variable viewfinder to go with my C-4 Geiss-modified.
While it fills-in a gap in my Argus collection, I was a little disappointed that it falls into the family of "shrinking-mask" variable finders, as opposed to the true "zoom-finder", which magnifies the image.
Also, in addition to some hazy optics, I'm not sure what the intent was with the clear window around the top circumference of the finder body, behind the front lens element (which also appears to have an Albada-type semi-silvering?). In bright light (daylight), the light coming through this "skylight" just seems to wash-out the finder image...
Just offering this as an observation for those seeking a user-friendly finder... this one doesn't seem to be the best thing out there.
The Argus Turret finder or "TV-set" variable finders are a lot easier to use (at least according to my middle-aged eye-bones!).