I was just checking ebay for a wideangle lens for my Pentax 645N and I came
across an adapter that will allow the use of Hassleblad lenses on my Pentax,
is there a downside to doing this?  Will it work seamlessly and not lose any
functionality?  What about aperture, will this be affected?

There's lots of nice Ziess optics out there, so it would be kind of cool to
be able to use them, but I don't want to make any compromises on
performance.

Thanks all!