I bought a new Tamron 150-600mm f/5-6.3 lens a month ago. I am a professional photographer and am not biased towards or against Tamron vs. Canon, as I own prime L-grade lenses from both companies. Unfortunately, this lens is not weather sealed, and after using the lens for two weeks outside, the amount of internal dust was atrocious. Regardless of being meticulous and using a blower at all times, the lens quickly absorbed dust onto the frontal glass element internally, including moisture, via the cork-screw barrel that retracts into the upper chamber. Closely inspecting the markings on the lens, I saw that it was manufactured in China, as opposed to Tamron's traditional Japan manufacturer, which was a big shock, so quality control has definitely been compromised in order to sell the lens at $1069
. In the end, the build quality really comes down to the poor engineering design from Tamron.
Additionally, image stabilization for action shots (specifically bird shots) is not reliable. Even though the proper autofocus point speed and tracking can be adjusted in the Canon 5D Mark III to compensate for the lag, shutter speed has to be at least 1/2000th+ of a second in order to prevent motion blur for hand held action tracking shots (coupled with f/6.3 on a cloudy day and ISO 1000-2000, this creates photos worthy of entry level DSLR bodies and stock lenses - which means not good!). Unlike my Canon 100-400mm f/4-5.6 L lens, which has 2 modes of image stabilization and creates very fast and stable shots, the Tamron 150-600mm lens only has one on/off VC switch with no additional stabilization mode selection settings. Gimbal shots are naturally improved, but AF adjustment at 15m to infinity is still sluggish when trying to focus on objects 200ft and further (creep still occurs with the limiting switch). I called Tamron directly, and their technical support team confirmed that their teleconverters are not compatible with this lens as Tamron engineers have officially discontinued all TC's and did not design this lens with the 1.4x or 2x in mind. Additionally, they confirmed that both converters should not be used with the lens, as unpredictable results can occur and are not guaranteed to work properly.
Static shots are amazing with very comparable MTF chart optical clarity to Canon, and portability of the lens is great
; nevertheless, I need a telephoto lens that is fast, reliable, and has excellent build quality for shooting Ospreys, Eagles, King Fishers, Herons, etc. while panning for fast track motion. Sorry everyone, but this lens is not quite the "big white killer" that many individuals thought that it would turn out to be. I too thought that this was the lens that would allow me to save several thousand dollars; however, I have now returned the Tamron 150-600mm lens for a full refund and consequently have to save up in order to purchase the real Canon 600mm f/4.0 L II (weather sealed, improved pre-set focus ranges, stabilization modes, etc.). On another note, even though the "Sigmonster" 800mm f/5.6 is less expensive than the Canon 600mm, I am not even going to touch it, given that it too is not weather sealed and that other professional birders have complained that the focus ring breaks over time, has a fragile body shell, and is extremely sluggish to maneuver; being confined to a gimbal for the majority of the time. In the end, you get what you pay for!