Both lenses show similar levels of vignetting wide open. I'd estimate the Tamron vignetting at about 1 stop of underexposure in the corers, wide open on a full frame sensor, across the whole zoom range.

Tamron's VC mechanism employs a three-coil system, whereby the three driving coils activate the shake-compensating VC lens groups electromagnetically via three steel balls. We spent 2 hours in the store making detailed comparisons using my MacBook (with 2 other guys in the shop offering very valued, experienced but un-biased opinion) including making crops of each image. On all settings, the Tamron edged out the Canon 70-300 fairly easily, and the Canon was excellent to start with! Against the 70-200 F4L, the Tamron loses slightly when wide open, but once stopped down to F5.6/8 the differences were extremely hard to find, with the Tamron only losing marginally at the corners. In several of the images I took, we really couldn't tell any difference between the Tamron and the Canon L - it even came to the point that we couldn't remember which images were from which lens, they were that close. Even though this lens does not have a wide aperture, the relatively long 300mm focal length is still able to create aIl Tamron 70-300 F/4-5.6 Di VC USD SP, nonostante sia stato prodotto nel 2010, è ancora uno degli obiettivi fotografici con le migliori caratteristiche e funzioni nella sua categoria. The SP 70-300mm F5-5.6 Di VC USD (Model A030) employs Tamron's esteemed image stabilization mechanism-VC (Vibration Compensation).

D700 / SP 70-300mm F4-5.6 Di VC USD / 2,832×4,256 / 1/320秒 / F10 / -0.7EV / ISO200 / 絞り優先AE / WB:晴天 / 300mm Both lenses are sharp wide open and improve a little on stopping down. However they can both be used wide open without worrying too much about image quality. Technically, the Tamron overall sharpness probably peaks at around f8 (center) and f11 (corner) at all focal lengths, but the difference between wide open and stopped down is quite small and shooting wide open (and hence with a faster shutter speed or lower ISO setting) will often give the best results.The bottom line is that even a sharp lens does not deliver sharp subjects if not focused accurately. D700 / SP 70-300mm F4-5.6 Di VC USD / 4,256×2,832 / 1/500秒 / F10 / -1.7EV / ISO200 / 絞り優先AE / WB:晴天 / 70mm

I can tell you this, the tamron 70-300 is sharp! It is sharp at 300 mm, it is sharp wide open (@300mm) and focus accuracy is almost 100%. I feel it is on the same level or better than the canon 70-300 L with respect to sharpness. Both canons where less sharp at 300mm wide open. The tamron is better. Where this lens stands out is focus accuracy. It may be due to my nikon d7100 body but focus is spot on any time. Only my first version of the canon 70-200 2.8 II L had better Sharpness and color. The SP 70-300mm F4-5.6 Di VC USD employs Tamron’s esteemed image stabilization mechanism–VC (Vibration Compensation) seen in both the AF18-270mm Di II VC (Model B003) and SP AF17-50mm F/2.8 XR Di II VC (Model B005). With VC, the photographer has the freedom to shoot at a shutter speed that is an extra four stops slower without having to worry about blurring. This makes capturing handheld, evening, night, and interior shots much easier. Pincushion distortion increases over the focal length range until becoming moderately strong at 300mm. Because the Tamron SP 70-300 mm is designed for use on cameras with a full frame sensor, when using it on a camera with an APS-C sensor, you won’t be troubled by vignetting. If you ever do encounter it, it must be a picture of a bird against a smooth blue sky made at maximum aperture and the longest focal length. Vignetting is simple to correct later with software if needed. Distortion Outre cette nouvelle motorisation ultrasonique, le télézoom accueille également un système de stabilisation optique VC (Vibration Compensation). La formule optique comprend des lentilles LD (Low Dispersion) et XLD (eXtra Low Dispersion) pour limiter les aberrations chromatiques.For its low price, the Tamron 70-300mm f/4-5.6 Di VC USD Lens delivers rather impressive overall image quality. Mounted on the full-frame Canon 1Ds Mark III, the lens doesn't betray any secrets - it's just a little bit softer at wide apertures. Otherwise it's mostly the same story as above - stop down to ƒ/8 to get maximum sharpness, and don't expect anything overly sharp at 200mm or 300mm. Also typical for a lens of this class is that the Tamron 70-300mm f/4-5.6 Di VC USD Lens has a variable max aperture. Autofocus: The Tamron uses a built in focus motor Tamron calls USD. On my Sony A100 which is an older body from 2006 the focus speed is alright, on a much faster body like the Sony A700 the focus is fast indeed. It isn’t on the same level as the Sony SSM motor or the pro motors from the other companies, but for the price it is very good. Accuracy is alright on both my bodies, it can miss at times in low light, but that might just be my cameras. I would give it a 3/5 for focusing, it is fast and good, but not going to exactly blow you away either. The chromatic aberration at all focal length/aperture combinations is reasonably low. Telephoto lenses are in theory sensitive to chromatic aberration. Therefore, the design often utilizes more expensive types of glass to combat chromatic aberration. In the design of this lens, which is made up of 17 elements in 12 groups exist, there are two lens elements with a higher refractive index (low dispersion & ultra low dispersion) included. That’s relatively few, and it keeps the cost down. And it seems to be reasonably effective. In the extreme corners you will, only at large magnifications of uncorrected RAW files, sometimes find visible purple and green edges at sharp contrast transitions. Those are easy to correct with software afterwards.