No, of course not
The Canon lenses were positioned further back to achieve identical framing as the Tamron at 270mm. Notice also not only the sharpness and crispness of the prime but its complete lack of color fringing (around the tire and within the metal rim). Subject distance approximately 100 feet. Anyway just a quick little comparison for those debating whether to get the Tamron VC superzoom or the Canon 300 f2.8 IS as their Hawaii honeymoon walkaround lens 
Tamron 18-270 VC @ 270mm f6.3
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Canon 70-200 f2.8 IS + Kenko Pro 1.4x @ 280mm f6.3
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Canon 300 f2.8 IS @ 300mm f6.3
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Canon 300 f2.8 IS @ 300mm f2.8 [wide open]
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Test results seem to be about on-par with what should be expected!




