Praktica Wide Angle Dilemma

[tron]

So im thinking of picking up a wide angle for my Praktica B100 (Praktica B bayonet mount). Im looking at the following wide angles offered in a B mount:

Zeiss 2.8/20mm ($400ish)
Pentacon Prakticar 2.8/28 ($75ish)
Pentacon 4-4.5/18-28 ($lots)

Could I use the following adapter and get an m42 screwmount wide angle instead? The m42 wide angles are much MUCH cheaper. I would still like to focus to infinity though, im not sure if the adapter takes the distance difference into account.

Adapter:
Hama 30541: PRAKTICA B to M42 Screw Lens adapter ring

 

[tron]

anyone?