Originally Posted by ph.
I occasionally use a contax ST. Its exposure is spot on and the finder is very bright, but I dislike the inaccuracy of using its focussing screen and find the original Leitz SL or the later R8 far better. The optics of both systems are entirely satisfactory - and can mostly be used on Canon digital bodies as well as on MFTs. If you like to focus manually, acommodating adapter chips need not worry you.
If it is inaccurate to focus it sounds like the mirror or screen is misaligned.