* I have the cheaper Tamron 18-200 preferred because the AF motor of the Sigma is much faster and quieter, and according to test reports, the picture quality will be much better.
* I have the more expensive Sigma 18-125 preferred because its high-speed AF motor even more responsive and the significant additional cost for me (determined existing) better image quality, but did not appear adequately in a shorter focal length.
Now I have the Sigma 18-200 tested on the Alpha 65 and Alpha 77 and compared to the kit lens Sony DT 18-55.
Result: The pictures with the Sigma are about 100 times sharper than the Sony 18-55 kit lens. The difference is truly amazing! While I hardly 18-55 at the sharpness of the Nikon D5100 (16MP, with the good 18-105) or Canon EOS 600D (18MP, with useful 18-135) zoom'm with Sony, manages the Alpha 65/77 with the Sigma at same focal length much more focus and image details as mentioned cameras.
Conclusion: As inexpensive superzoom the Sigma may not exhaust the full 24 Megapixel the new Alphas, perhaps, but it is enough to beat the current 16 or 18 MP cameras significantly.
Thus has been confirmed in this example, that the Sigma as stated in test reports quickly become one of the better entry lenses, although behind Nikkor 18-105 and Sigma 18-125, but in front of the Tamron 18-200, probably before the Canon 18-135 and well ahead of the Sony 18-55.
