In terms of EU Community Law this is complicated stuff. What follows is a very abbreviated summary ignoring lots of potential arguments and provisions.
Article 81 (1) of the Treaty of Rome prohibits:
all agreements between undertakings...which may affect trade between Member States and which have as their object or effect the prevention, restriction or distortion of competition within the common market, and in particular those which:
(a) directly or indirectly fix purchase or selling prices or any other trading conditions;
( limit or control production, markets, technical development, or investment;
and a bit more.
All contracts which contravene this Article are void (i.e of no effect).
However Article 81(3) provides that the Commission can exclude certain species of agreements from this prohibition.
We then go to Regulation 2790/1999 (“the Vertical Agreements Regulation”). A vertical agreement is an agreement between 2 parties who are on different rungs of the supply/distribution ladder - i.e. a Manufacturer and a Distributor or Retailer. Article 2 of the Regulation exempts vertical agreements from the prohibition (as long as they don't have a couple of features which are referred to as "hard core").
But where a vertical agreement has an exclusivity element (i.e. Manufacturer A will only sell to Distributor B or Distributor B will only buy from Manufacturer A) then the exemption only applies where the buyer has less than a 30% market share.
This is where the fun starts. What is the market? In the case of digital backs is it a market for digital cameras (which would include consumer cameras)? Or is it only Medium Format Digital Backs regardless of size and cost? Is it Medium Format Digital cameras (which would include the Mamiya ZD)? Is it only Medium Format Backs which fit Hasselblad? Or Contax? Or LF cams?
Lots of potential arguments.