I've received an email today from Dr. Milos Mladek from Austria, here's what he asked me to post here:
"As far as I know there were two versions of the Narciss: the regular version, and a variant for endoscopy (gastroscopy or so). The cameras differ in the „ground glass“. The civilian version really has a normal ground glass, but the endoscopic version has a plain optically neutral glass with a cross of hair lines. While the ground glass has a real image that is then watched by means of an eyepiece (in the finder), the image of the endoscopic Narciss is a „Luftbild“ (=German, it would translate into something like „air image“). The reason why they included this plain glass with the hair cross is simple: the image is brighter by far, and with a little practice this kind of viewfinder can be used as comfortably as a normal one. All you have to do is to focus the endoscope (or the relay lens in the tube that hands the endoscopic image to the camera) on the interesting detail (e.g. the gastric ulcer) and the hair cross at the same time (!). They must be sharp at the same time. Sounds complicated, but is not. The Narciss on your website is such an endoscopic version with aerial image. But normally the endoscopic Narciss was delivered with a different viewfinder which was exclusively thought for endoscopy. It looks quite different and can be distinguished instantly. It renders an upside-down (and laterally correct) image and also has a different magnification (the regular camera has a correct image of about 0,8x, while the endoscopic viewfinder is about 1,25x magnification and has a round field of view). The aerial image is outstandingly clear, bright, and a joy to use. The endoscope was attached to the camera by a screw-in (normal Narciss thread) helicoid tube with built-in relay lens that can be focussed from beyond infinity to about 10 cm distance, so that it can handle all virtual distances of the endoscopic image (the endoscope normally renders an image that is thought for the human eye, with a comfortable viewing distance of about 30-50 or so centimeters)."
http://www.ussrphoto.com/UserContent/3052016_01 Narciss.JPG
http://www.ussrphoto.com/UserContent/3052016_02 there were two viewfinders.JPG
http://www.ussrphoto.com/UserContent/3052016_03 the two viewfinders.JPG
http://www.ussrphoto.com/UserContent/3052016_04 endoscopic viewfinder.JPG
http://www.ussrphoto.com/UserContent/3052016_05 .JPG
http://www.ussrphoto.com/UserContent/3052016_06 .JPG
http://www.ussrphoto.com/UserContent/3052016_07 there is no ground glass, but a clear glass with hair-cross.JPG
http://www.ussrphoto.com/UserContent/3052016_08 the viewfinder has no prism, yet a simple mirror.JPG
http://www.ussrphoto.com/UserContent/3052016_09 the endoscopic relay lens can be mounted instead of the normal lens.JPG
Best regards,
Milos and Vlad