Nikon and Canon professional grade lenses are much more expensive than the Contax 645 Carl/Zeiss.
Yes, this is about new vs. used, but Nikon/Canon used lenses are not much different from their used ones.
I think Nikon/canon could be more convenient than Contax 645 or any other medium format, that's all?
No wonder Hasselblad H's sale is dropped badly.
This only tangentially has anything to do with Hasselblad or Phase One for that matter. The tangent is the little issue matter of supply and demand. Compared to Nikon and Canon and the other marginal 35mm based Digital SLR cameras on the market, medium format cameras occupy an increasingly small share of the demand pie. Inside that slice since Contax 645 systemhas been discontinued for at least 5 years years and it commands virtually zero demand even in the marketplace for used cameras . With virtually no demand, prices fall.
On the plus side as a consumer that means you can get some really great deals on the terrific lenses that were made for the Contax 645 system.
Yes Sigma makes some lenses that perform very well (And Canon and Nikon some lenses that are bad) but let's see how they hold up in the long term. In the past build quality has been a problem for Sigma (And Tokina, etc.)