Tamron's design philosophy for mirrorless lenses has been clear: light, compact, and priced so mere mortals can afford them. Most of its models are strong optically, using shorter zoom ratios to keep size and costs down. The 70-300mm F4.5-6.3 Di III RXD ($549) is in line with others in the series in sizing—it's the smallest, lightest 70-300mm you can get for a full-frame camera—but it isn't as good a lens optically as others, like the 70-180mm F2.8 or the Sony FE 70-300mm F4.5-5.6 G OSS.
Affordable, But Not Cheap
The 70-300mm F4.5-5.6 comes in at half the price of the Sony FE 70-300mm, but doesn't feel cheaply made. Its outer barrel is quality composite plastic, similar to what you get with many pricier lenses, and Tamron includes internal seals to prevent moisture from creeping into your camera system.
It measures 5.8 by 3.0 inches (HD), weighs 1.2 pounds, and supports 67mm filters, the same size used by all of the Sony E mirrorless lenses Tamron has released to date. The lens isn't too far off in size when compared with the Sony FE 70-300mm, but is notably lighter—Sony's first-party option weighs 1.9 pounds.
A reversible lens hood is included, as are front and rear caps. The barrel telescopes out when zooming, standard for a compact telezoom, so the lens is nearly twice as long at 300mm as it is at 70mm. There's no sort of lock to keep it short for travel, but tolerances are tight enough and the optical block is lightweight, so I didn't notice the zoom creeping outward when stowing my camera at my side, at least not with a new copy.
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On-lens controls are minimal—you just get control rings to set the zoom and focus manually. The manual focus ring sits close to the mount and is finished in plastic, with the raised ridges that are common on camera lenses. The focus ring has a softer, rubberized wrap, with the same ridged texture.
Autofocus is quick and essentially silent; the lens supports all of Sony's focus features, including eye detection and tracking. The manual focus experience is also quite good—automatic frame magnification kicks as an assist, and the lens is able to make very fine adjustments. Breathing is minimal, but the focus ring doesn't offer a linear response, nor can it be easily geared for follow focus, so I'd recommend sticking to autofocus for video.
The macro capability isn't fantastic, nor is it overly limiting. The minimum focus is 31.5 inches, measured from the image sensor at 70mm, for a meager 1:9.4 macro, and while you'll need to pull back to 59.1 inches at 300mm, you'll net a larger 1:5.1 reproduction ratio. You won't find it limiting for portraiture, but be prepared to pull back, instead of leaning in, if you want to hone in on the details of the world. The Sony FE 70-300mm is a better option here, it focuses close enough to capture objects at 1:3 life-size.
Stabilization is also left out. It's less of a concern for full-frame owners—all but Sony's now discontinued first-generation a7 series include 5-axis in-body image stabilization. With the our standard body for lens testing, the Sony a7R IV, I netted blur-free shots at shutter speeds as long as 1/15-second at 300mm. It's important, especially considering the narrow aperture—in dim light, you'll need to use a longer shutter speed, or push the ISO higher, to net a sharp photo.
If you use an APS-C model without IBIS, you'll want a lens with an optical stabilization system. The Sony E 70-350mm F4.5-6.3 G OSS is a better fit—it's priced higher, around $900, but it's a better match for an a6400 or a6100.
Blurred Edges
I tested the Tamron 70-300mm F4.5-6.3 Di III RXD along with the 60MP Sony a7R IV and Imatest software. Lab tests show the lens to be a good performer in the central area of the frame, but results are very soft as you look away from the middle of your image.
At 70mm f/4.5, the pair nets very good resolution in the middle third of the frame (4,200 lines), but softens considerably when you look anywhere toward the periphery; the off-center average is just 1,400 lines, resulting in blurred details on the a7R IV.
See How We Test Cameras and Lenses
Narrowing the aperture a bit lessens the effect, but you'll want to go down to f/11 to get off-center results that show good resolution. Compare this with the Sony FE 70-300mm—we've not had a chance to test it on the a7R IV, but with the 42MP a7R II it captures photos with much more consistently good resolution from center to edge.
Tamron's 70-300mm gets a little bit better when zoomed in. At 135mm f/5, it nets nearly excellent center resolution (4,400 lines), and while there's definitely some off-center softness, it's not as extreme as at 70mm—we see 2,800 lines on average, a decent result. At f/8, resolution improves through almost all of the frame, and at f/11 and f/16 we see clear results from center to edge.
It takes a step backward at the 200mm and 300mm focal lengths, though. At 200mm, we once again see strong central sharpness give way to significant blur when shot at f/5.6 or f/8—you don't see images with good off-center resolution until f/11.
At 300mm, the maximum aperture is just f/6.3. The lens shows more consistent performance here, but resolution takes a step back overall. It delivers an okay 3,300 lines at the center, with off-center results dropping a bit, but not too much, to bring the average down to 3,000 lines—an acceptable result.
In-camera corrections do a good job with other aspects of performance. We see no visible distortion in images and very little darkening at the corners and edges of the frame. If you work in Raw format, you'll see some of the latter, as well as some pincushion distortion when zoomed in. Adobe Lightroom, our standard for processing Raw images, includes a profile to match in-camera corrections—it cleans up those issues with a single click.
Worth Spending More
Tamron has done an overall excellent job with its lenses for the Sony full-frame mirrorless camera system. Its series of F2.8 zooms cost much less than first-party options, and while they don't quite offer the same level of quality as a G Master, we recommend the 17-28mm, the 28-75mm, and the 70-180mm F2.8 quite highly.
The 70-300mm F4.5-6.3 Di III RXD isn't quite as successful. It meets a very aggressive price point—$549, less than half the cost of Sony's full-frame FE 70-300mm—and is built well, including seals to protect your camera system from moisture. But there are some real drawbacks.
If you're on a budget and you want a zoom for your full-frame Sony with some reach, another Tamron lens, the 28-200mm F2.8-5.6, is just an overall better performer, with an attractive $729 asking price. It doesn't offer the 300mm reach, but it ticks all the other boxes you'd want for a light, affordable full-frame zoom.
If you use an APS-C camera, the Tamron 70-300mm is a bit more attractive thanks to strong center sharpness across the APS-C confines of the full-frame sensor. The lack of optical stabilization is a concern, though, and Sony's E 70-350mm G OSS is there as an alternative—it's a better lens with more zoom power, for around $1,000.
The Tamron 70-300mm F4.5-6.3 Di III RXD is a telephoto lens that costs and weighs less than competitors, with serviceable image quality for a modern optic.
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