9 out of 10 points and recommendedsmall and lightweight for its range, very good overall image qualityzooming not smooth, lower contrast and edges less sharp at the long end
The lens is well built and seems to be a very solid contruction. Autofocus is fast and almost silent (however, still noticeable more noisy than the autofocus in my 14-140). OIS works well, but is a bit noisy if you use the lens for filming in relatively silent surroundings. Zooming is okay, but not as smooth as with the 14-140 (might be a problem when shooting video).reviewed January 19th, 2011 (purchased for $700)
Even wide open sharpness and contrastat are excellent in the range between 100-200mm. Stopping down only improves the edges marginally. Here the lens is on par with the performance of the 14-140 in its sweet spot around 20-50mm and noticeably better than the 14-140 at the long end. Zooming from 200 to 300mm, contrast gets somewhat lower and wide open the edges are a bit blurry, especially at 300mm. At 300mm the performance is quite similar to the 14-140 at 140mm: still decent, but stopping down to f=8.0 is advisable for obtaining sharp edges and optimal contrast. Distortion is not an issue, but there is some vignetting wide open, especially at 300 mm.
Overall, I think that the 100-300 is an excellent supplement to the Panasonic 14-140. You not only get the extra range (comparable to 5,6/600 for full frame!) for shooting wildlife, sports etc. - you also get a noticeably superior performance to the 14-140 in the range between 100-140mm.