Welcome to the world of DOF adapters. The main function of such DOF adapter is to enable a shallow DOF in small CCD cams like Z1 or HVX202. This will enhance the "film look". It works by focusing your cam onto a imaging element. The DSLR lens will be focused onto this element as well. Therefore the adapter becomes an intermediate interface. Y it can give u more shallow DOF is a big topic, u should visit the companies n research yourself. Lots of factors.
Lens >> Adapter >> Image Flip >> Camera
Due to the original image being upside down and roted 180 Deg, new adapters all have built in prism flips to correct the final image. The main thing u will face is lost of light. The best being 1/2 stop lost so far. The market leaders are Cinevate Brevis and Letus. Others like Redrock, SG Pro and Cine city (india) also have various offerings.
Please take note that this is very costly thing to mess with cuz u need $ for the lens, rails and adapter. U can go for used lens, old zoom len with manual control aperature n focus to cut cost. Rails are a must since the flips are in place now.
Goodluck.