That is, the โholeโ in Tamron is formally f2.8, but either this is the design of the lenses, or the lens is too contrasty (its pattern is much more contrast than that of the Sigma), the output image is darker than the standard one at f2.8. That is, in fact we have not f2.8, but somewhere f3.2-3.5. Surprise awaited me when I contacted the Tamron office in Hong Kong. When I asked what converters this lens works with, they answered, theoretically, โthat it should work with 2x and 1,4xโ (I donโt quote the words verbatim, but the meaning is exactly that - that is, in the office itself they donโt know which converters their lens works and answers in theory). So 2x converter is beyond him - only 1.4x