Yes auto focus works well. the canon is 3 Lbs and the tamron weighs 4.3 Lbs. yes i do have a canon 1.4 II CONVERTER which does auto focus with good light if you tape the pins.this will add another 300.00 to the canon combo almost double the price of the tamron. With the converter it makes the 400 =560mm. here is a site that tells you how to tape the pins on the converter. also with the converter on the 400mm you can forget about shots of moving objects. the only real drawback of the tamron is it is heavy to handle for hand shots. this is new to me and have not even tried shooting flying or moving targets. http://www.michaelfurtman.com/taping_the_pins.htm good luck
Canon 70D Thanks. I also have a one year old canon 100-400 L lens and compared several shots. both lens were very close in image quality. Tamron is a great buy at 1069.00 compared with the Canon at 1560.00