Are you kidding? The comparison isn't even close. Rest assured, you did not make a mistake.





The Tamron is f/3.5-6.3, which means it won't AF on any EOS body @ 270mm, whereas the 300/4L IS will, as it is over 1 full stop faster. With the EF 1.4x II Extender, the 300/4L IS becomes a 420/5.6, and you *still* have AF.


Furthermore, the 100/2.8L macro IS again has a wider maximum aperture than the Tamron. At the same focal length (100mm), the Tamron is f/5.6, which is two stops slower.


Although the Tamron says "macro," it is not a true 1:1 macro. Its maximum magnification is 1:3.45.


The Tamron is nowhere near as sharp as either Canon. Chromatic aberration is much, much more severe.


The only things that the Tamron has over the two Canon lenses is a continuous focal length range from 18-270mm, and lighter weight. But you pay for it in a significant loss of image quality, loss of true macro magnification, and no AF at the longer focal lengths.





In summary, you pretty much get what you pay for. One superzoom is not going to replace two L primes.