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I've currently got the Tamron 90mm but have the chance to sell it to a colleague. Is the Sigma 150mm f2.8 OS a better lens? I'll be using it with a 5D mk3 that I intend buying very soon.

Has anyone compared the image quality of the two lenses directly?

(I've already discounted the Canon 100mm as I've got a couple of lenses that would cover portrait shots etc. hence the potential leap to 150mm.)

Any thoughts?

Thanks,

Guy.