Focusing helicoid for mount large format lenses on medium and 35mm format cameras

Pick up an interesting helicoid. It is designed to mount large format lenses on medium and 35mm format cameras. I am surprised; this helicoid is factory production, not DIY. This means that such a device was in demand of amateur photographers and professionals before I saw some homemade focusing devices such as the "trombone" mechanism. 

The device consists of two parts: the helicoid with a Hasselblad bayonet (Soviet “Bayonet V”) for medium-format cameras. And an adapter for cameras with M39 thread. It is screwed into the back of the helicoid. 

The total length of the helicoid with an adapter in an infinity focusing - 147mm. 

The maximum extended - 187 mm. The angle of rotation is 540 degrees; the helicoid turns one and a half turn. The front part extended by 40mm. The front thread has a diameter - 60mm. Front helicoid diameter holes to a depth of inside 44mm. Next comes a decrease in the hole to a diameter of 50mm. Inside, the helicoid is plastered with black velvet, which eliminates the parasitic barrel glare. Through the ring M39-M42 and M42-Nikon adapter, you can mount it on the Nikon camera. 

Focusing helicoid with lens I-51 4,5/210, mounted on Nikon SLR camera Lens I-51 4,5/210 with this helicoid mounts on camera without any problem. As well as other photographic and projection lenses 13x18 cm format or larger. Helicoid is not suitable to mount a smaller format lens (9x12 cm or smaller) because the flange distance of such lenses is not too long. For them, it is recommended a smaller helicoid. This helicoid can also be interesting for the macro shooting in the reproduction ratio of 2:1 or more.