Contax to EF lens mount adapter

[rawrasaur]

So, Ive just become interested in photography a few months back and picked up myself a digital rebel xt, with the 18-55mm stock lens. (I absolutely abhor this lens when I really open it up)

I have recently come into ownership of a few Zeiss Contax lens, all made in Germany, and have been wondering how big of a difference there is between the $150 adapters and the $10 ones.

Thanks in advance!