This is an unusual and rare 90 degree finder for the FED cameras. It was made in the 1930's by the FED commune.
The finder allows to compose picture while holding the camera perpendicularly. A pivoted mirrored window (see rear view) makes it possible to use a rangefinder. I believe there was a Leica accessory of this design, and it was copied by the Russians.
(Source www.fedka.com)
Known serial numbers:
903 _______ seen on eBay
904 _______ A. Berry collection
1812 ______ Avto Metreveli
1967 ______ imcphoto collection
2053 ______ Fed book (1939)
2404 ______ Communist cameras
3991 ______ seen on eBay
4314 ______ David Tomlinson
4453 ______ Michel's coll.(With box)
5456 ______ seen on eBay
6032 ______ Christian G. (Niko80)
6108 ______ Avto Metreveli
6171 ______ seen on Fedka.com
6682 ______ Fotomuda
7010 ______ SovietCams
7555 ______ seen on eBay
7740 ______ seen on eBay
8138 ______ seen on eBay
8516 ______ Michel's coll. (incomplete)
8749 ______ Michel's coll.
8789 ______ Leica shop
9256 ______ seen on eBay
9263 ______ seen on eBay
9758 ______ seen on eBay
9884 ______ seen on eBay
9987 ______ seen on eBay
11623 _____ seen on Molotok
12077 _____ Chris Sabine collection
12145 _____ seen on eBay
12358 _____ seen on eBay
13362 _____ seen on eBay
13484 _____ seen on eBay
13594 _____ seen on eBay
14718 _____ seen on eBay
14838 _____ PYC collection
14909 _____ Jacques collection
15662 _____ seen on eBay
15981 _____ seen on eBay
16016 _____ seen on eBay
100411 ____ PYC collection (s/n confirmed, one digit seems to have been doubled)