I can now use my elder PK lenses on the G1, which makes a telephoto option less pressing. I can use any Pentax lens in truth, but the new ones with no aperture ring will only shoot wide open. Initial tests look pretty good, but I need to investigate how I hold the camera with a heavier lens. Often while shooting the ISO-adjust screen pops up, which suggests that I'm pressing something without knowing. Since the adaptor has zero electronics I cannot blame it directly.. but right now I'm not sure what is going on.
The adaptor plus 50mm lens is a match for the 14-45 kit lens. Length and weight are very similar, and the 50 just a bit wider.. and it's a Rikenon so it even takes the 52mm filters! At first glance IQ looks good. The Vivitar 28-105 and Rikenon 35-135 also seem to do well, though at almost 500g these are the ones that make me adjust iso. I've yet to try the Big Gun (Sakar 28-200); lack of IS will be a problem in the gloom of December.
shot with Rikenon-P 35-135mm f/3.5-4.5
I've been struggling with the m4:3 telephoto question for a while now, with three options looking good for different reasons. The obvious answer is the Pana 45-200 with OIS, built for the G1 and able to combat shake. In the lightweight corner is the well-regarded Olympus 40-150, about half the weight and less telephoto - it would not be stabilized so stopping at 150 would be a sensible tradeoff. On the third hand, the Lumix 14-140 would do it all and be stabilized, for a bit more money net of selling off the 14-45. Current sentiment is to stick with number one; the 14-45 is very good and it's tiny, so selling it holds little appeal. Lack of IS can be learned now with the Rikenon 35-135, if that lens suffers from shake the 40-150 will fare no better. At least I have something to get me closer now.. and I get to learn all about the G1's white balance options! ;^)