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Tested the new GM FE100400 lens on my A7RM2 today with a quality printed color and B&W target. The GM100400 is an excellent sharp lens at f6.7 and outstanding at f8 and f11. Wide open (f5.6) at 400mm it is quite good but some blurring of 2 & 3 point type is seen. At f8 2 point type is SHARP at 400 mm and almost equally sharp at 560 mm and f8-11 with the Sony 1.4X TC. The 100-400mm lens even operates reasonably well at 800mm with the Sony 2X TC, where 3 point type is fairly good and 6 point type is sharp. Of course contrast is lowered with the TC’s but not significantly for the 1.4X TC. No chromatic aberration was noted with this lens. I compared the GM 100400 with my (generation 1, 2014) Tamron 150-600mm lens. With a Sigma 2X TC at 720mm, 3 point type was good and 5 point type reasonably sharp. Without TC, at 600mm the Tamron is known to be much less than optimal and in this comparison test that proved to be the case: at 600mm very good type had to be 5-6 point type and even larger type could not be said to be truly sharp. Plus all tests required chromatic correction with the TAMRON lens. I did not test tonight at 500mm with the TAMRON, which should give better results than the 720mm using the 2X TC. In each test I moved the tripod so as to fill the frame with the target, so there is no correction needed for distance.