I have often read that you loose IQ if you use a tele-converter so I wanted to see for myself. I used a Vivitar series 1, 70-210/3.5 & a Vivitar 2x converter for the experiment on my Panasonic G1. I set a tripod up on our balcony & shot the bird bath in the back yard with a salmon tin sitting in it. The ISO was set @ 100 & I used f5.6 for the shots. 1. Lens set ~ FL 200, no converter, 1/1600s 2. Lens set ~ FL 100 with 2x converter to equal FL 200, 1/400s There is definitely a loss of light & IQ with the converter in this simple trial. However it looks as though the converter shot has a greater DOF.