Fuzzy edge in secondary monitor

I connected my iMac to a secondary display via the miniDP-to-HDMI adapter. But the windows in the secondary monitor has fuzzy edges and blur text. The monitor is sharp and crisp when I use it in Win 7. And there is no such problem when I connect to my HDTV with the same miniDP-to-HDMI adapter/ HDMI cable.

Any one can shed some lights? Many thanks.

I have the same exact problem

I am a proud owner of a new iMac 21,5" and I also aqcuired an 18,5" LG Monitor model w1943c to use as a second display for audio edition. But my lg stays just like your second monitor does. Unable to work with. The images are blur and no config seems to work with this... What should we do? Please someone help!! Is it because I am using Lion OSX ???