I had, until recently, the Tamron 18-270mm F / 3.5-6.3 Di II VC LD ASL IF in action, the first of its kind (Travel Zoom) on the market and was also very happy except for a few things. But as that's just so, only in comparison to the difference disclosed. For some time Sigma offers a similar lens. I ordered it and compared, because I was not happy with some details at Tamron. That was especially the loud and slow autofocus and slipping out of the lens when not locked together down there once again, owners know what I mean. The ultrasonic motor is superior to the "normal driving" the Tamron clearly quieter and above all faster. The slightly longer focal length is only slightly noticeable and virtually no selling point for my test. But what ultimately completely pulled me to the side of the Sigma, were the results of my private photo tests. I have photographed with two lenses multiply the Siemens star, even at close range (1.00 m) and from a distance (approximately 6.00 m) with my Canon EOS 450, with autofocus and aperture priority mode. When focus I had the feeling that the Sigma was restless than the Tamron. However, the image control on the PC showed a surprising and not the expected result. The Sigma gave sharper images than the Tamron. I did not believe the first test and repeated this. Changing the lenses was might be annoying, but the result could not be reversed. Whether so severe that about 90 grams and about 100,00 expensive Sigma should be preferred over the Tamron everyone must decide for themselves now. Two small differences are to be mentioned. The locking of the push is on Tamron right hand grip on the camera, the left of the Sigma, the lens Hand 'practice (s) in my opinion. For a 5 year warranty Tamron and Sigma 3 years with online registration. Had it been given both lenses two years ago and been a comparison is available, I would have like a little late now, opted for HSM and would also get the sharper lens.
