Wildlife and sports photographers immediately recognize the attractiveness of the telephoto zoom focal length range of this lens. Lenses that include 150mm in their focal length range are plentiful (and very useful), but no big brand name zoom lenses as of this review date include 600mm (other than the $7,999.00 Sigma 300-800mm f/5.6 EX DG APO IF HSM Autofocus Lens). Combining the great zoom range, vibration control and USD AF in a compact package with a value price is a recipe for an amazing lens.
Getting the right focal length range is critical in the lens selection process and focal length range is, as I already indicated, a huge attractor for this lens. Even the large, expensive Canon EF 200-400mm f/4 L IS USM Lens stops at 560mm with its built-in extender in place.
Does the 150-600 VC really go to 600mm and is it really 150mm on the wide end? While I'm glad that we don't have to deal with lenses named 93-376mm (for example), zoom lenses with unusually wide and/or long focal lengths (or lenses with an unusually long range of focal lengths) are sometimes suspect in their focal length ratings with marketing purposes being a driving force.
If I make the dangerous (but likely at least close to correct) assumption that the Canon EF 600mm f/4 L IS II USM Lens is a true 600mm lens, I can use its angle of view to compare it to the 150-600's angle of view at 600mm. On a full frame body, the 600 L IS II properly frames a 23.62 x 15.75" (600 x 400mm) target at 33.92' (10.34mm) while the Tamron (at 600mm) frames the same target at a modestly shorter distance of 32.23' (9.83m). The fractional multiplier created from those two distances would indicate that the Tamron's longest focal length is more like a 570mm lens (95% of 600mm).
The Nikon 600mm VF Lens frames this target from even slightly farther than the Canon. However, differences in distortion (the Canon 600 has negligible distortion while the Tamron has mild pincushion distortion at both focal length extents) complicate this actual focal length determination method by causing the lens to need to be closer or farther away to properly frame the target. So, we do not really know the answer to my question.
Regardless of the true focal lengths, I can tell you that 150mm is a mid-telephoto focal length that is not real wide even on a full frame body and the 600mm focal length setting has a very narrow field of view that brings your subjects in very close – incredibly close on an APS-C/1.6x body. It seems like no subject is out of reach for this lens. I love it.
For an example of the 150-600mm focal length range, I take you to the steps of the Philadelphia Art Museum for a view down the Benjamin Franklin Parkway that features Philadelphia's Washington Monument.
These above images were captured with a full frame Canon 5D Mark III with an f/8 aperture. Put this lens on an ASP-C/1.6x FOVCF sensor format DSLR and you get an amazing angle of view equivalent of a 240-960mm lens on a full frame body.
Wildlife photographers including bird photographers (who can never have too much focal length) and sports photographers needing to reach far into a field or track are the two groups who are most excited by what these focal lengths can do for them.
The male mallard with its iridescent head feathers shown below was captured at 600mm with an f/8 aperture.
There are many other photographers who can make use of this wide 4x focal length range. Photojournalists with restricted access to their subjects, paparazzi and law enforcement groups will find this focal length range useful. Portraits, especially the tightly framed variety, are on this lens' to-do list.
Landscapes are additional subjects included in this lens' capabilities. Long focal lengths are great for making colorful sky photos from even modestly nice sunrises and sunsets. While long focal lengths will make you want to photograph very distant subjects, under some situations, too-distant subjects should be avoided.
The above picture is a 100% crop from a 600mm picture of a steel railroad bridge. No, I did not use an "Art" filter on this image. Yes, the steel should be straight and sharp. No, this blurry image is not is not the fault of the lens.
When present, heat shimmer/haze will create optical distortion that will diminish the quality of long distance photos. It was 13° F (-11° C) on a clear, sunny morning when I photographed the distant railroad bridge. Apparently the warmer water in the river flowing under the bridge and in the foreground was creating turbulence for the light waves. The lesson here is that using the long focal lengths to photograph distant subjects must be done with consideration to this effect.
Sometimes, sharp is not what I'm looking for anyway:
The unique color in the above 309mm photo of Fairmont Falls (by the Philadelphia Art Museum) is thanks to mixed light sources. Getting interesting color from a monochromatic scene on a heavily overcast day involved carefully timing this shot. The image is custom white balanced using the falling water, which leaves the rest of the photo blue and red toned. The blues are from reflections of a late day cloudy sky. The reds are reflections of street lights. The motion-blurred water is thanks to a 30 second f/11 exposure.
Like most zoom lenses with long focal lengths, the Tamron 150-600mm f/5-6.3 Di VC USD Lens is a variable max aperture lens.
This means that wide open aperture exposure settings will change as the lens is zoomed from 150mm to longer focal lengths.
You camera will automatically account for the change in auto exposure modes, but manual modes require a manual exposure adjustment in most cameras.
Here is how the max aperture step down looks in the Tamron and a couple of other similar lenses:
|Canon EF 100-400mm f/4.5-5.6 L IS USM Lens||100-129mm||130-259mm||260-400mm|
|Nikon 80-400mm f/4.5-5.6G AF-S VR Lens||80-134mm||135-249mm||250-400mm|
|Sigma 150-500mm f/5-6.3 DG OS HSM Lens||150-173mm||174-312mm||313-500mm|
|Tamron 150-600mm f/5-6.3 Di VC USD Lens||150-225mm||226-427mm||428-600mm|
The Tamron 150-600mm VC Lens performs similarly to the Canon and Nikon models shown above and better than the Sigma, but with a rather narrow max-available wide aperture of f/5, this is not an ideal lens for stopping low light action. A max aperture of f/6.3 at 428mm and beyond makes this lens is even less ideal for stopping low light action at those focal lengths. The sharpness-reducing effects of diffraction kick in with some strength at f/11 through f/16 (depending on the DSLR being used), so there is a somewhat narrow range of ideal apertures remaining for use. Fortunately, those remaining apertures are quite useful.
Effects of the narrow max aperture that are especially welcomed are the size and weight savings enjoyed by this lens. Open the max 600mm aperture by 1 1/3 stops to f/4 and this lens would be a monster.
VC (Vibration Control) is important/useful with narrow max aperture lenses and especially important with telephoto lenses. The image in viewfinder jumps when VC starts, but this VC implementation is very quiet during use. With an ear near the lens, a hum can be heard while VC is working and a light click is audible when VC shuts off.
At 150mm, this is a relatively large and heavy lens. With the weight aiding to a steady hold and with ideal conditions, I can get sharp images nearly 100% of the time with shutter speeds as long as 1/15 of a second for nearly 3 stops of assistance. The keeper rates slowly drops off beyond this point until about 33% are sharp at 1/6 sec (4 stops) and about 25% are sharp at 1/5 sec (4 1/3 stops).
At 600mm, a light lens is hard to hold steady and VC is a big help. However, I still found that I need a 1/100 sec. shutter speed for solid percentage of sharp handheld shots under ideal conditions – for less-than-3-stops of assistance. Outside in the wind? None will be sharp at 1/100. Even with VC enabled and a full frame body in use, critically framing a subject while handholding this lens at 600mm is challenging.
The following with and without VC comparison photos of a pencil drawing were captured at 150mm with a 1/5 second shutter speed.
When a lens pushes the extremes, especially when it has a reasonable price, I am usually suspect of the image quality it is going to deliver. And image quality is always very high on my importance list. While the Tamron 150-600mm f/5-6.3 Di VC USD Lens is not going to challenge Canon's big super telephoto lenses in this regard, I am quite pleased with its performance.
Starting with sharpness ... wide open aperture image quality starts off decent across a full frame sensor at 150mm. At 200mm, a slight improvement can be seen with slightly better corner performance. At 300mm, a bigger improvement is seen with corners again seeing a nice improvement. At this point in the focal length range, image quality is quite good across the frame. Of course, the wide open aperture is now 1/3 stop narrower at f/5.6, but 300mm f/5.6 remains sharper than 150mm and 200mm at the equivalent f/5.6 aperture.
Results at 400mm are similar to 300mm. At 500mm, results again look similar to 300 and 400mm, but CA (Chromatic Aberration) begins to detract from corners. This lens delivers its softest results at 600mm f/6.3. That this focal length also has the strongest CA, with CA visible even near the center of the frame, compounds the image softness issue. While 600mm f/6.3 results are not terrible, they are not very exciting either.
Stopping down to f/8 at 150mm results in a nice improvement in sharpness, though full frame corners retain some blur. At 200mm, f/8 results are looking quite good across the frame. There is a sharpness improvement realized by stopping down to f/8 at 300mm and 400mm, but with already good wide open aperture sharpness, the difference that stopping down makes is not so significant at these focal lengths. At 500mm, stopping down to f/8 is only 2/3 of a stop narrower than the wide open f/6.3 aperture setting and the difference realized in image sharpness is not big. Same at 600mm which remains the least sharp focal length.
There is little difference in sharpness realized by using a narrower-than-f/8 aperture on this lens except at 600mm where there is a nice sharpness benefit to stopping down to f/11 – especially in the corners. Otherwise, there is little sharpness benefit to stopping down to f/11.
Overall, the 300-400mm range is the sweet spot for this lens, but the 200-300mm and 400-500mm ranges are quite nice, 150mm is not bad and the over-500mm focal length range is not too bad if stopped down to at least f/8 and ideally to f/11.
Though I'm sure that having "600mm" on the box is going to sell a lot of these lenses, I was thinking that it might have been better if Tamron stopped the range at 500mm. It is hard to resist going for the max focal length in the heat of the action, but how much do you really give up by stopping at 500mm – even if the subject is not framed tightly enough? In some semi-controlled outdoor testing (clouds were influencing lighting somewhat but the two images were captured about 1 minute apart), I determined that up-rezzing 500mm images to 600mm-equivalent framing (using DPP) delivers near-similar pixel-level image quality. The f/8 100% crops shown below were taken from just above center-of-the-frame captures from a 5D Mark III body.
I see a slight edge for the 600mm example, but ... the difference is very slight. I suppose that not having to up-rez an image is indeed an advantage to having 600mm.
Comparing the image quality results of this lens to the Canon super telephoto models will show you what you didn't pay for, but comparing this lens to the still-significantly-more expensive Canon EF 100-400mm f/4.5-5.6 L IS USM Lens paints a much nicer picture. I'll compare these two lenses in more depth later in the review.
A small amount of CA is apparent in Tamron 150-600mm VC images at 150mm. At 200mm, CA level are negligible. CA then gradually increases until becoming, as already mentioned, quite strong at 600mm.
With a wide open aperture, expect to see between 1.0 and 1.6 stops of vignetting in the corner of full frame body-captured Tamron 150-600 VC images. These amounts are mild with the strongest shading seen at 600mm. APS-C/1.6x format body owners will not likely notice any corner shading.
If you get a bright light, such as the sun, in the corner of a telephoto focal length frame, you should expect to see some flaring. And while this is indeed the case with the Tamron 150-600, the amount of flaring is quite low. At least through 400mm. Because of the risk of sun/heat damage to the camera, focal lengths beyond 400mm remain untested.
Most zoom lenses have barrel distortion at their widest focal length, but the Tamron 150-600 breaks the rule by showing mild pincushion distortion at 150mm. Also breaking the rules is that the distortion changes very little over the entire focal length range.
The Tamron 150-600mm f/5-6.3 Di VC USD Lens and its 9-blade aperture delivers mediocre background blur quality. Out of focus highlights are characterized by having a bright, radiating outer circle containing many concentric inner circles and a hot spot that moves from the center toward the outer circle as the location in the frame moves in the same direction.
Overall, the image quality performance delivered by the Tamron 150-600mm f/5-6.3 Di VC USD Lens is quite good for the price point of this lens. Especially so if you can avoid the over-500mm focal lengths by moving closer to your subject.
Utilizing Tamron's USD (Ultrasonic Drive), the 150-600 VC quietly internally focuses with FTM (Full Time Manual) focusing supported. Focus speed is reasonable as long as the lens locks focus immediately. I add that condition because I find this lens going focus hunting too frequently – even under good light. This issue can be a bit maddening at times and I missed some wildlife shots because of it. AF fails to lock sometimes even in good light with a high contrast subject (most frequently when in a strongly out of focus condition to start).
My Tamron 150-600 required a relatively large AFMA adjustment of -15 on the 600mm end to correct a back-focusing problem on both 5D III and a 1D X bodies. Focus calibration was correct at 150mm, so in the case of this copy of the 150-600 VC, a camera with the ability to adjust focus calibration independently at wide and telephoto focal lengths may be needed. Of course, a trip to Tamron service should accomplish the same result.
Sometimes, evaluating a lens' auto focus performance can be complicated and this was the case with the Tamron 150-600 VC. It is not realistic to test every possible auto focus situation with all compatible cameras at all available focal lengths, but I threw wide a variety of scenes, subjects, colors, motions, lighting, etc. at this lens. To remove as much camera auto focus performance influence as possible, I am primarily testing with Canon's best-available AF system in the EOS 5D Mark III and 1D X at this time.
I spent a good amount of time informally and formally testing one shot AF accuracy with overall accuracy being mostly good. I did run into situations with more varied accuracy results, but I have not been able to identify what causes this issue. I already mentioned the focus hunting issue – sometimes this lens would simply refuse to focus at all with, at most, a short focus hunt attempt. An advantage to the relatively narrow apertures on this lens is that they are not too stressing to AF system accuracy.
AI Servo with fast-approaching subjects is a much bigger challenge to AF systems. I primarily used the best-available center focus point for this testing. Overall, with over 1,500 images captured and reviewed, my results from this lens were mostly good. Occasionally, I had a complete burst of images that were out of focus and sometimes when this occurred, there was not even focus point indication showing for the raw files (in the DPP quick view window). Closer subjects at longer focal lengths and lower light levels were unsurprisingly the most challenging to this lens. Based on the amount of hunting this lens does in one shot AF mode, I was surprised at how well it worked in AI Servo mode.
Update: Tamron updated the firmware installed on the Canon mount Tamron 150-600 VC lens, specifically targeting improved AF performance. Initial reports are that the update made a noticeable improvement in AF accuracy. This update was issued sometime mid-northern-hemisphere summer 2014. Lenses with older firmware can be sent to Tamron to receive this update.
The 150-600 VC provides a focus limiter switch. Choose between the limited 49.21' (15m) - 8 range and the full extent focusing range. Limiting the focus distance can reduce focus hunting in some scenarios.
Filters installed on this lens will not rotate during focusing. Subjects remain about the same size during full extent focus adjustment at 150mm, though you can expect to see some subject size changes by the 600mm end. Of course, at 600mm, the subjects quickly become unrecognizably blurred with focus distance change.
This lens is not parfocal. While the focus distance setting does not change too much from one focal length extreme to the other, you should plan to refocus after zooming in or out.
The manual focus ring is very smooth with proper dampening. The 120° of focus ring rotation is very nice at 150mm, but feels short/touchy at 600mm. Annoying for manual focusing is that the subject framing shifts slightly to the left or right depending on the direction the focus ring is being turned. Most noticeable at 10x Live View, the shifting happens regardless of VC being on or off. The shifting diminishes rapidly/suddenly at focal lengths over 500mm.
Focus distances in ft and m are provided in a window.
The Tamron 150-600mm f/5-6.3 Di VC USD Lens' MFD (Minimum Focusing Distance) is longer than the other lenses in this class, but with significantly more focal length available, it still matches the others in MM (Maximum Magnification). The 0.20x MM is about average for all non-macro lenses.
|Nikon 80-400mm f/4.5-5.6G AF-S VR Lens||68.9"||(1750mm)||0.20x|
|Canon EF 100-400mm f/4.5-5.6 L IS USM Lens||70.9"||(1800mm)||0.20x|
|Sigma 150-500mm f/5-6.3 DG OS HSM Lens||86.6"||(2200mm)||0.19x|
|Tamron 150-600mm f/5-6.3 Di VC USD Lens||106.3"||(2700mm)||0.20x|
Extension tubes can be used to reduce the MFD, but the MM will not be dramatically reduced for this lens. However, the difference extension tubes make can be just enough to get the tighter framing you need on small subjects. Tamron considers this lens to be not-compatible with extenders, though you might find a third party model that will work – perhaps Kenko has a teleconverter that will meet this need. Note that AF may not be supported with a compatible extender mounted.
Build Quality & Features
I frequently use a 600mm lens, but not one this small and light.
Yes, I know that the hood is partially cropped out of the with-hood pictures. I have two standards for the site's product images. One is for large lenses (such as the Canon/Nikon super telephoto lenses) and the other is for more-normal sized lenses. Because I wanted to be able to directly compare this lens with the more-normal sized lenses, I opted for the smaller lens size product image standard. Here is a full extended-with-hood picture:
The Tamron 150-600mm VC Lens' rubber-ribbed zoom ring is been given a large amount of real estate and it is very easy to find. This ring has a seemingly long 148° of rotation between extents and the rotation seems even longer due to the somewhat wide diameter of the ring.
The zoom ring rotates in the Nikon direction – camera-clockwise to increase focal length. The zoom ring has mediocre smoothness – you can tell that you are moving a good amount of lens while turning the ring. Support the end of the lens while turning the ring and the adjustment happens much smoother with the slip-stick action gone.
With the size and weight of this lens, you may need to plan on needing a left hand position change or two while zooming a significant amount. As the left hand moves out from under the lens while zooming, the holding grip becomes more awkward due to the weight of the lens. Holding the camera solely with the right hand during a hand position change is also modestly challenging. Mounting on a tripod or monopod of course eliminates this small issue.
The focus ring is positioned to the rear of the zoom ring. While this design is not my preference, it is normal for similar lenses. The heavy lens requires a balanced left hand grip position, and I find myself holding this in in the space between the two rings while using my fingertips to control the zoom setting. This keeps my hand under the lens for support.
A zoom lock switch is provided for fixing the lens at its fully retracted 150mm position. There are not too many lenses made today that need such a switch (at least when they are new), but this lens definitely needs the switch. With the lens hanging downward (such as when the camera hangs from the neck strap), this lens will quickly extend as you are walking. I used gaffer tape to hold the lens fully extended for capturing some of the product images in this review.
This zoom lock switch is especially appreciated because of the rather long 3.12" (79.3mm) length of zoom extension on an already long lens. When hanging from my 5D III's neck strap, the hood on this extended lens reaches 5" (127mm) above my knee (I'm 6'/1.8m).
Ideal for outdooor use is that this is a weather sealed lens. The lens body is plastic construction (very common today). Even when fully extended, the entire lens remains solid.
The switches (3 of them) and the switch panel are nearly flush with the lens barrel. All of the switches are two-position-only (there is no getting confused with a mid-position setting) and an audible, solid click into position is felt.
Here is how the Tamron compares to a few other lenses in terms of size and weight:
|Model||Weight||Dimensions w/o Hood||Filter||Year|
|Nikon 80-400mm f/4.5-5.6G AF-S VR Lens||55.4 oz||(1570g)||3.8 x 8.0"||(95.5 x 203mm)||77mm||2013|
|Canon EF 100-400mm f/4.5-5.6 L IS USM Lens||48.7 oz||(1380g)||3.6 x 7.4"||(92 x 189mm)||77mm||1998|
|Sigma 150-500mm f/5-6.3 DG OS HSM Lens||67.0 oz||(1900g)||3.7 x 9.9"||(94 x 252mm)||86mm||2008|
|Tamron 150-600mm f/5-6.3 Di VC USD Lens||68.8 oz||(1950g)||4.2 x 10.1"||(105.6 x 257.8mm)||95mm||2013|
|Canon EF 200-400mm f/4 L IS USM Ext 1.4x Lens||127.8 oz||(3620g)||5 x 14.4"||(128 x 366mm)||DI 52mm||2013|
|Canon EF 500mm f/4 L IS II USM Lens||112.6 oz||(3190g)||5.7 x 15.1"||(146 x 383mm)||DI 52mm||2011|
|Canon EF 600mm f/4 L IS II USM Lens||138.4 oz||(3920g)||6.6 x 17.6"||(168 x 448mm)||DI 52mm||2011|
For many more comparisons, review the complete Tamron 150-600mm f/5-6.3 Di VC USD Lens Specifications using the site's Lens Spec tool.
While this lens is big and heavy when compared to most consumer lenses, it is rather small and light relative to the more serious wildlife lens options (such as the three up-to-2x heavier focal length-sharing Canon options I included in the table above). Carrying and handholding this lens is not a problem, though you will know that something is in your hand. Critically framing a handheld 600mm photo is a challenge that a heavier lens may better facilitate.
As always with a big lens, use of a tripod or monopod makes life more comfortable. The Tamron 150-600 ships with a metal tripod mounting ring to make use of those supports easier. The ring allows the lens and camera weight to be properly balanced over the support vs. a very front heavy situation created by the lens hanging from a supported camera. The ring-mounted camera is also quickly and easily rotated for the ideal orientation.
The 150-600's tripod ring is quite strong, though at 600mm, you will be able to see some flex exhibited in the viewfinder if pressure is applied. I'm also pleased with the smoothness of this ring.
The ring can be removed by loosening the thumbscrew and rotating to a marked position where the ring slides off of the mount end of the lens. A camera cannot be mounted while the ring is removed, but I appreciate the lack of a sometimes-uncomfortable hinge that this design permits. A bit disconcerting is that the thumbscrew can be completely removed from the other side of the ring. The screw is captive, but you can have the ring attached to the lens only by the rigidity of the split metal ring.
This tripod ring provides a single threaded insert, so I highly recommend using lens plates with safety nubs to prevent twisting. The Wimberley P20 Lens Plate is a good choice for this lens and can be seen in many of the pictures in this review. The additional length that this lens plate adds to the ring's foot better facilitates carrying the lens using the nicely finger-grooved foot. The P30 would give you even more range for adjustment.
That this big lens accepts filters is a positive feature, but the 95mm filters it accepts are both large and expensive. The hood (included) is so large on this lens that, if in use, a protection filter is seldom needed. A circular polarizer filter can be a valuable addition to a kit with this lens in it. The Tamron center-and-side-pinch lens cap can easily be installed and removed even with the big hood installed for use and light gloves on.
With a long focal length in use, vibrations must be guarded against and the big lens hood is quite adept at catching wind. For this reason, you might consider removing the hood in windy conditions.
A case is not included with the Tamron 150-600mm f/5-6.3 Di VC USD Lens and your standard telephoto zoom lens case will not likely be big enough to hold this very long lens. I've been carrying the 150-600 mounted to a non-gripped body (primarily the EOS 5D Mark III) in a Think Tank Photo StreetWalker. With the lens hood reversed, this combo consumes most of the length available in this case. I ran over 3 miles (5K) one evening with this lens and pack on my back with no discomfort.
Positioned above from left to right in their fully retracted positions are the following lenses:
The same lenses are shown below in their fully extended states with their lens hoods in place.
Obvious is that much of the Tamron's lens hood is not shown. The extended Tamron without the hood mounted is nearly as long as the other two extended lenses with their hoods attached. Of course, the Tamron extends 200mm longer than the other two lenses. Use the site's product image comparison tool to create your own comparisons.
The Sigma 150-500mm f/5-6.3 DG OS HSM Lens is a telephoto zoom lens that also has a very long focal length built in. Roger Cicala (LensRentals.com) graciously allowed me to buy one of his best Sigma 150-500s when the lens first became available. Unfortunately, its image quality is far enough behind the Tamron that it does not merit considering. Here is this comparison. LensRentals.com does not carry this Sigma lens in its massive inventory.
The Canon EF 100-400mm f/4.5-5.6 L IS USM Lens is the Tamron competitor that I was most anxious to make comparisons against. The Canon, though now a somewhat old design, is a very good and very popular lens. It has Canon's longest zoom lens focal length without an internal or external extender included in the optical path.
From an image sharpness comparison, these two lenses are more similar than different at wide open apertures with the Tamron holding a slight edge in the center of the frame in some comparisons. At 400mm, the Tamron is noticeably sharper. At f/8, the comparisons are even closer with the Tamron retaining a corner advantage at 400mm. The Tamron also has less CA at 400mm.
The Canon 100-400 L obviously has as wider angle focal lengths than the Tamron 150-600, so the Canon outperforms the Tamron at all focal lengths below 150mm. Similarly, the Tamron has longer focal lengths than the Canon and therefore far outperforms the Canon at all focal lengths above 400mm. Add a 1.4x extender to the Canon and it becomes a more-similar 140-560mm lens, though with a 2/3 stop narrower max aperture at 560mm. All Canon EOS DSLRs can autofocus with the Tamron's f/6.3 max aperture, but only high end 1-Series models and the 5D Mark III can autofocus with Canon combo's f/8 max aperture mounted.
Here is an image quality comparison between these two lenses at 600mm vs. 560mm and f/8. I give the Tamron the edge in the center and the Canon the edge in the outer image circle. The two lenses are very similar at f/11.
The Tamron wins the flare comparison by a considerable amount. The Canon has slightly less distortion, and has especially-tidier corners in the 560mm vs. 600mm distortion comparison.
I prefer Canon's Ring USM AF over Tamron's USD. The Canon uses a push-pull zoom design while the Tamron is rotational. A benefit to the push-pull design is that your left hand remains under the lens for constant support and fast focal length changes. A disadvantage is that it is easy to pull the lens away from your eye while zooming. Your call on which is the better option for you.
Determining which lens is better for the wallet is easy. The Tamron 150-600 VC price tag is about 2/3 of the Canon 100-400 L price tag at review time, making it a great value lens.
The Tamron 150-600mm f/5-6.3 Di VC USD Lens is available in Canon (reviewed), Nikon and Sony mounts. My standard disclaimer: There are potential issues with third party lenses. Since Tamron reverse engineers (vs. licenses) manufacturer AF algorithms, there is always the possibility that a DSLR body might not support a (likely older) third party lens. Sometimes a lens can be made compatible by the manufacturer, sometimes not. There is also the risk of a problem that results in the lens and body manufacturers directing blame at each other. Tamron USA's 6-year warranty duration is far superior to Canon's standard 1 year warranty.
This highly anticipated lens has been a very fun lens to evaluate. While autofocus performance and over-500mm image quality get my vote for this lens' weaknesses, the Tamron 150-600 still has a great deal going for it. The Tamron 150-600mm f/5-6.3 Di VC USD Lens is defined by attractive image quality over a great focal length range with a relatively compact, light, reasonably well-built design that includes Vibration Control and a very attractive price.
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