What is the white square near the viewfinder of the Fujica GW690?

Question

What is the purpose of the white square and hole near the viewfinder of the Fujica GW690? It's a mechanical camera without a light meter so I can't imagine what they are.

Answer 1

As you can see in the image below from the service manual, the volume behind these two features is occupied by the view finder assembly.

^{Image source: manualslib.com}

^{Image source: manualslib.com}

The round hole is for one of the two optical paths of the range finder optics. The white rectangle is used as a light source for the frame line indications inside the view finder.

^{Image source: Rick Oleson}

Answer 2

The white square is a frosted glass pane which allows light in to illuminate the frame lines in the viewfinder. Many rangefinder cameras have something like this, in particular all M Leicas, until recently when they changed (I presume) to illuminating the frame lines with some internal light source. The second small window is the other half of the rangefinder: an image from this is superimposed over the centre of the image in the viewfinder and by arranging for the two images to line up you can triangulate the distance to the object you are looking at, which is how rangefinder cameras work.

(Note that not all rangefinder cameras have the frosted glass thing: I suspect you only need it if you want to have frame lines which attempt to do parallax correction & so move as focus changes and/or multiple sets of framelines. Certainly I have a Kodak Retina IIS which has a combined viewfinder and rangefinder with framelines but does not have the frosted glass window: however the framelines are fixed.)