Wednesday, June 3, 2015

Tamron SP 24-70mm F/2.8 Di VC USD Review


Tamron SP 24-70mm F/2.8 Di VC USD

Image stabilization is the closest thing photographic-wise to Pavlov's conditioning stimuli experiments. Just the mere mention of it gets people salivating, even with lenses that don't particularly suffer without it. Normal-zoom lenses fall into that particular category; the two pro-spec lenses by Canon and Nikon don't have it and many people get by well with out it. Still, the thinking goes that more must be better; if a constant f/2.8 zoom is good than adding image stabilization must be better.

To that end, we have the Tamron SP 24-70mm F/2.8 Di VC USD, the first stabilized full frame professional-quality 24-70mm lens, though likely not the last. If you read between the lines, neither Nikon or Canon have introduced image stabilization into their designs because of compromises that it would introduce into the optical quality of their lenses. This also seems true for crop lenses as well; early Fujfifilm roadmaps had the XF 16-55mm f/2.8 R LM WR including an image stabilization feature, only to be left out in favour of outright optical quality. Tamron themselves are perhaps the most classic example of this; the venerable original  17-50mm f/2.8 was a near-pro quality lens, at least in terms of image quality; the VC version lost a bit of something and became more of a hobbyist's lens.

So, we all want image stabilization and a fast aperture. Did Tamron get it right this time?

Construction and Usage


Tamron 24-70 VC on Nikon D750

The lens is unmistakably by Tamron. Like the 150-600mm and the 15-30mm, the overall impression is of a sleeker version of the classic gold-ring Tamron lenses from the early 2000's. The lens is still plastic, but the texture has a unique flat semi-gloss texture. What catches people off guard with this lens is how big it is. Traditionally, Tamron has been known for producing lenses that are smaller and more compact than the competition. This was especially true of the fondly-remembered and venerable Tamron 28-75mm f/2.8 XR Di LD. However, the company's lens designers seem to have taken a different tack in different years, as both this and the Tamron 15-30mm f/2.8 Di VC USD are as large as their first-party counterparts. The weight savings is gone as well; it is heavier than the Canon 24-70mm f/2.8 II, but not as heavy as the Nikon.

Dimension-wise, the Tamron is virtually the same size as the second version of the Canon 24-70mm f/2.8. Though not as long as the Nikon, it also means that it shares 82mm filters with the Canon; in other words, this is a fat lens that will also drive up the cost of filter usage. Build quality-wise, the Tamron is the least solid-feeling of the three, but it isn't necessarily cheap feeling. Though all of these lenses have a rubber lens-mount gasket, only the Nikon is completely sealed in that the rear lens element is flush to the chassis and does not move. On the Tamron and Canon lenses, the rear lens element moves during zooming, leaving an air-gap at the lens mount. Theoretically this means that the Nikon is less prone to getting dust inside the lens, but the real world difference is likely academic.

Which brings us to the first and last word about crop-frame use with this lens. Though it can be used on a DX Nikon or an EF-S Canon camera, the size and weight make for something an unwieldy walk-around combination. The Tamron is good as a flexible portrait-zoom type lens on crop frame, but there are cheaper and smaller alternatives for APS-C users.

Operation


Tamron's USD focus mechanism works in the same manner as Canon's USM or Nikon's AF-S technology. Autofocus action is quick and sure; just slightly behind the speed of the first party lenses, but not enough to make a difference in real world shooting for the vast majority of shooters.

Likewise, the VC system works as advertised, allowing for roughly four stops of hand holding advantage; three stops with a higher hit rate. That translates into a working minimum shutter speed of  of approximately 1/5s to 1/10s with the lens zoomed out. You won't see the same amount of advantage at the wide end, as this (and most) image stabilization system bottoms out around 1/5s in any case.

Optical Quality


Being of the same purpose, the Tamron, Canon and Nikon lenses all behave similarly with barrel distortion at the wide end, and pincushion-to-little distortion at the long end. The Tamron has slightly more barrel distortion at 24mm, but not enough to be objectionable for most photographers.Likewise, all three lenses show similar characteristics when it comes to vignetting: heaviest at the wide end and at widest aperture, while being minor when zoomed-out and stopped down. Vignetting for the Tamron is more or less inconsequential at the middle 35-50mm focal lengths when used wide-open, where it improves slightly from the long and wide ends. This is good news for the Tamron; the build in vignetting and distortion control that Canon and Nikon use for their in-camera JPEG engines don't apply to third party lenses; in order for a lens like the Tamron 24-70 to have a good showing, it needs to be optically good without the software correction. 

Detail and resolving power are comparable as well. All three lenses are sharpest at the wide end and lose some bite as you zoom out. There isn't much to differentiate other than the fact that the Nikon might be a bit more consistently sharp across the frame when zoomed out. Thankfully, the field curvature of the Tamron is fairly flat (like the Canon), meaning that the plane of sharpness doesn't curve away from the user towards the corner of the image. This may matter to some users more than others, but it is a generally good for the overall rendition of the image as the amount of defocus blur falls off more progressively as the distance to the focus point increases.

Lateral chromatic aberration is extremely well controlled. Usually this is where the difference between third-party lenses and mainline lenses shows up, but the Tamron is fairly close to the Canon in terms of fringing in harsh light, and is actually better than the Nikon. The story is the same with longitudinal chromatic aberration; the Tamron may be a tad bit behind, but the difference is imperceptible in real-world shooting.

Bokeh



Because lens optical performance is a complex topic, the objective description of such is beyond the scope of this blog. Though there are many aspects to quantify (resolving power, field curvature, distortion, aberrations, etc.), a general sense of a lens’ character can be determined without resorting to lab testing. The following  are two aspects; background blur ("bokeh") with the subject short distance, as well as differences in perceived sharpness at the extreme edge of the image frame.

All of these lenses have "good bokeh" by undemanding standards. Both the Tamron and the Canon generate smooth circular out-of-focus highlights. Both also display an "onion bokeh" pattern, though the Tamron is a bit harsher. Subjectively the Nikon has the smoothest background bokeh of the three, though it doesn't produce perfectly round highlights when used wide open.

Vs. Canon EF 24-70mm f/2.8L II USM


Here is the lens set at 50mm vs the Canon f/2.8 II using EF-mount lenses on a Canon 5D Mark III. First, here is the sample seen. Crops are taken from the focus target and from the display rack behind. For reference, the focus target is approximately 4-5 feet in front of the camera.

Tamon 24-70 VC, f/2.8 (Canon Mount)

And now the crops, with the area of focus at the top and a crop taken from the center of the image, roughly six feet behind the focus target.




Here is how the lenses compare when you compare the extreme edge of the frame


Overall it's a good show. The level of detail is comparable between the two lenses, but the Canon has just a bit more contrast, which shows up in the slightly deeper blacks.

Vs Nikon AF-S NIKKOR 24-70mm f/2.8G ED


Here is the lens set at 50mm vs the Nikon f/2.8, which was shot on a different day using F-Mount lenses on a Nikon D750. First, here is the sample seen. Crops are taken from the focus target and from the display rack behind. For reference, the focus target is approximately 4-5 feet in front of the camera.

Tamon 24-70 VC, f/2.8 (Nikon Mount)
Once again, the crops. Setup is similar, but not exactly the same as the previous set.


Here is how the lenses compare when you compare the extreme edge of the frame



Same story again. Similar detail rendition, only in this case, the Nikon shows a slightly softer background blur.

Overall, the Tamron 24-760mm is a lens that is competent and easy to work with, but it falls just short of giving the optical "wow" factor that the best lenses produce. The resolution is definitely there, but there are some apparent drawbacks... not obvious ones, but just a few ticks here and there that fall short of what Nikon and Canon are able to do with their lenses. The overall rendition is also a fairly neutral; it is certainly sharp in the centre, but again, it doesn't have that microcontrast "bite" that really good lenses can produce.

All that is moot, of course. What shortcomings there are optically pale in comparison to the benefit of in-lens image stabilization. Simply put, it's a lens that can be shot in a more care-free manner, and it opens up more possibilities to stop down in lower light situations.

Comparisons


Left to Right: Canon 24-70 f/4, Canon 24-70 f/2.8 II, Tamron 24-70VC and Nikon 24-70 f/2.8

The Canon f/2.8 II lens is the priciest of the bunch. In some ways it is better than the Tamron, particularly in build quality and overall bokeh rendition, but the Tamron has better overall sharpness when zoomed out and is for all intents and purposes, closely matches the Canon in all other measures of optical quality. The difference in price is considerable, and is likely the first and most pressing matter for most people.

The Canon EF 24-70mm f/4 USM L IS is the logical price alternative to the Tamron.  Both lenses cost roughly the same amount of money, and both are image-stabilized. The f/4 Canon shares a similar optical quality to the f/2.8 II; that is to say, it is like the bigger lens, just that it stops at f/4.The Canon is the more compact of the two, being shorter and smaller in diameter. It is often overlooked because the f/2.8 II is the object of most people's lust, which is a shame because the 24-70mm f/4L is a terrific lens in its own right. That said, the obvious advantage of the Tamron is that the maximum aperture is one stop larger, and to add to that, the lens is most definitely usable with the aperture wide open.

For Canon users, the first 24-70mm f/2.8 might be an option, but only if obtained from the used market. It's the value choice, but its a conscious choice to spend less at the cost of less image quality.

In the same vein the Sigma AF 24-70mm f/2.8 EX DG HSM is a the value choice for both Canon and Nikon users. This lens shows its age, as it pre-dates the Global Vision "ART" era, but the saving grace is that it is cheap compared to the other choices. Like the first Canon 24-70mm f/2.8, the optical quality is a step behind all of the other lenses mentioned in this group, but that is mitigated by its lower price.

The Nikon 24-70 f/2.8 is the longest and heaviest of these lenses, and is the one that is likely the next in line to be updated...with it be with VR image stabilization or with PF fresnel technology... and whenever that may be. Build quality is substantially better than the Tamron. Image quality is just a tad bit better in all regards, except at the wide end where it where it is let down by high lateral colour fringing and a non-flat plane of focus. Assuming that hand-holding stability is not an option, the Nikon is a better lens. Neither of these lenses are small, but the Nikon feels particularly weighty... partly because of its length and partly because it truly is a heavy lens. The Nikon 24-70mmm doesn't feel truly at home until it's on a metal-frame camera like the D810; mount this lens on that camera and the combined heft mitigate some of the need for image stabilization.

Conclusions



It's time to come clean. During the assembly of this blog post, the sample files got mixed up and it took some time to accurately sort out which file came from which lens. That's the crux of the issue; if you know what you are looking  for the Tamron 24-70VC isn't quite as good as the mainline competition, but for significantly less money, the difference is minor for all except the most demanding people. In this regard, the Tamron is closer in spirit to the ideal of what a normal-zoom is than the Canon or Nikon alternatives. Normal zooms are about convenience; they shine in run-and-gun situations where the environment is changing and its important to get the shot and move on. In situations like that, it's not necessarily about getting the perfect shot, but adapting to get the shot that you need... as perfectly as possible. To that end, the Tamron 24-70mm f/2.8 Di VC USD works as well as you would hope it would.





With thanks to Broadway Camera

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