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Message: <blockquote data-quote="RJM" data-source="post: 1442804" data-attributes="member: 66340">I think the price difference accurately reflects the zoom range and the extra SLD element in the Bigma. FWIW, <a href="http://www.popphoto.com/Reviews/Lenses/Sigma-150-500mm-f-5-6.3-DG-OS-HSM-APO-AF" target="_blank">PopPhoto.com rates the 150-500 Excellent</a> across the zoom range on prints up to 8x12. Unfortunately, they seemed to have recently removed all the graphics lab charts from their lens testing . Looking at Sigma's own MTF charts for these lens, the 150-500 actually is a little sharper in the center with more contrast. It does seem to suffer from more astigmatism though at the edges. But on a cropped camera, these lens would be identical. I would say any percieved IQ differences in posted images has more to do with the human elements. I am quite pleased with the results I'm getting on the Nikon D90 with targets under 50m. At longer distances, the 82mm objective lens is not large enough to compete with the resolution typical of the 125mm objective lens in a 500mm prime.  Regardless, I am willing to sacrifice some IQ for the walkaround handheld capability the 150-500mm provides. I only print 5x7 or view the keepers on my HD TV though. cheers,Rick</blockquote>