During my telelens tests I had an opportunity to try allmost all of the Sigma models, except for 100-300 f4 that was not available at Sigma representative stock. Thanks to my fellow nikonian, Mr. Kerry Pierce from Detroit, I did get one for testing, but in remote, "cyber" way. What we did was splitting the procedure: Kerry did the toughest part; shooting the selected subject the way I usually do. He send the pics and I did the editing in PS. Sigma 100-300 f4 was shot at f4, f5.6 and f8, while Bigma full open only. No postprocessing done for 100-300, but 50-500 shots were corrected for brightness (all of them were slightly underexposed). Besides, an experiment was made with contrast enhancing and sharpening for the Bigma pics. This can be seeing in the lower left corner of all 3 tests. Result is pretty close to otherwise better 100-300 pics!