This lens does not need to be stopped to focus, it maintains sharp images even in the most extreme conditions. I have owned this lens for over 3 years; Bought by Revain in February 2010 for $1,600 (yes, Sony has raised the price several times since). This lens replaced my old Minolta 100-400 which was a 'good' lens but was a bit disappointing at 400mm unless it had an aperture built in. This lens will not disappoint you! Sharp at all focal lengths. I usually shoot with my hand wide open to get the fastest shutter speed and NO loss of sharpness at this setting. It's worth every penny. For 30 years I've been told to buy the best glass you can afford and have always tried to make do with sub-par lenses. so far this lens, and wow. With quality Sony glass, you definitely get what you pay for. This one really convinced me. I've since added the 70-200G and the CZ24-70 to my lineup and they're all definitely Keepers!
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