http://www.scopecity.com/detail.cfm?ProductID=8246
Change the focal length of 1100mm (F/7.3) to 840mm (F/5.6).
For sale is a rare and discontinued Takahashi TOA SUPER REDUCER that was made to cover a 645 format image circle.
Comes with both machined aluminum end caps and original box.
Very rare. $1850