Zooming is all part of the fun - it's seems typical of how these things work.
If you don't mind, I have a question for you - I'm also using a Canon FD 50mm lens on my "homebrew" attached to my HC1, and I'm having an issue with focus being off away from the center.
Could you please let me know if you get sharp focus from edge to edge with your setup? For example, compare:
http://i120.photobucket.com/albums/o...35mm_no_fc.jpg
to
http://i120.photobucket.com/albums/o...m_attached.jpg
Thanks.