Throughout this review, I intend to make comparisons between the Tamron 24-70 and the Canon 24-70mkII
as I know many people (myself included), debate long and hard between the purchase of these lenses.
A bit of background:
I've owned this lens for about 2 years now and have used it exclusively on the 5D3. To give you an idea of how much it gets used in comparison to my other lenses, take into consideration these numbers from my lightroom catalog; I currently have 2663 images in my catalog and 952 of those images (35%) were captured through the Tamron SP 24-70mm f/2.8 Di VC USD. The next closest lens is my 70-200II with 424 images (16%) . That comparison alone is strong testament to how well this lens has performed. I find myself grabbing this lens quite often for those times that I don't have any one specific objective. Going to a fair/festival? Family party? Wedding? Hike? Day at the park? Winery? Yup...this is the one lens that almost always makes the trip. Three reasons for this; versatility of the focal range, sharpness, and IS. This lens does everything quite well.
It is extremely difficult to find anything negative to say about the images coming from this lens. Sharpness, even wide open @ f/2.8, is never a factor in my decision to use the aperture. Is the Canon 24-70mkII sharper? At 70mm, yes. At 24mm, no. (This was compared between my copy of the Tamron and a friends copy of the Canon) Are both lens beyond sharp enough for large prints or heavy crops? I would say, absolutely yes. There comes a point when one has to ask the question how sharp is sharp enough. I'm extremely picky and admit to pixel peeping, but I'm quite satisfied. Corner sharpness is comparable between the two, but Canon does have the edge. If you are looking at corner sharpness @ f/2.8, I would say "Who cares?". Personally, I've never needed sharp corners in an image that I intentionally shot wide open (not to say that it can't happen). If you are looking at corner sharpness @ f/5.6 - f/8, then the differences between the two lens is negligible IMO. Point here being, if you are planning to shoot landscapes and absolutely need razor sharp corners, then my opinion is that neither of these lenses will get the job done. See below for full size and 100% crops taken at 24mm.
There are many people that regard the bokeh of this Tamron as a major negative point, citing "onion" bokeh as the problem. The characteristics of bokeh are multi-factorial and vary based on the setup of each individual shot. I have yet to take a shot and notice this "onion bokeh" without actually looking for it. For all practical purposes, it has not been an issue for me, not even once. See below for full-size and 100% crop images taken @ f/2.8.
AF Accuracy and Speed:
This is the Achille's heel of this lens. I have had the opportunity to use the Canon 24-70mkII side by side with this lens and I was able to appreciate a practical difference. The Canon is a bit more "snappy" when locking focus and overall a bit more accurate under certain circumstances. The Tamron does not perform poorly in this area, and actually quite the opposite. However, the Canon just performs slightly better. It's difficult to quantify how much better, but after using the two lens, my gut tells that the Tamron is about 80% as fast as the Canon when focusing from MFD to infinity, 99% as accurate in good lighting, and 80% as accurate in poor lighting. I have been able to overlook this shortcoming due to the fact that during important, difficult low-light situations, I'm reaching for a fast prime, not a 2.8 zoom.
This one is easy. Tamron has it and Canon doesn't. Do you need IS in this focal range? That's for you to decide, but personally, it has helped me get shots that I wouldn't have been able to capture without the stabilization. I don't recall how many stops of stabilization Tamron claims, but I can get about 3-stops in real life situations. For handheld shots, that's about 1/10sec shutter speeds at 70mm and almost a full 1sec exposure at 24mm.
Both lenses are built like tanks. The first thing I noticed when picking up the Tamron was the weight of the lens. It was heavy, it felt solid, and there was nothing that seemed as though it could easily break. The same goes for the Canon. The switches for AF/MF, VC On/Off, and Zoom Barrel lock can be "difficult" to locate and operate blindly. The switches could have been slightly larger with more tactile surface area. (I'm nit-picking here). Both lenses are weather sealed. Canon has the typical 1yr warranty. Tamron has a 6 year warranty. That is a huge plus IMO and proof that the company believes in the quality of their product.
Current Cost (1/27/15):
Tamron $1300 new
Canon $2000 new
IMO, the winner in this category is quite obvious. The Tamron is the better value lens.
Overall Performance and Image Quality:
Canon is superior.
However, the grey area begins to creep into the frame...
For the pro-shooter who uses photography as a primary source of income, and/or is using the lens for weddings and can't afford to miss a key shot, Canon comes out on top by a slim margin. (Slim because as mentioned above, Tamron suffers in low-light but most photogs are using their primes for these situations). For just about everybody else, I believe the IS (VC) of the Tamron at least evens the playing field between the two lenses, and may even elevate it to the top spot (and not just because of the cost difference).
Photography is my primary hobby and also a source of supplemental income. For these reasons, I would have a hard time justifying an additional $700 for what I would consider better AF and a marginal improvement in sharpness. In doing so, I would also have to justify paying $700 to lose image stabilization and a 6 year warranty. Still, the cost was NOT the reason I decided to purchase the Tamron 24-70...it was the IS (VC). A highly effective stabilization system coupled to the high ISO capability of modern sensors allow for great performance in a variety of shooting situations.
When I first received this lens, I literally tried to convince myself not to like it. Deep down, I was hoping to find reason to return the lens and order the new Canon 24-70. It took me a solid 3-4months to completely lose the lust, but I believe it's finally gone. The Tamron has been more than good enough for my purposes, even with knowing that the Canon outperforms the Tamron in AF speed and accuracy. I don't know that I will sell this lens any time soon, and certainly not until Canon releases a 24-70 f/2.8 with IS. If you are on the fence, try the Tamron first.