On my NEX6 and a6300 I always used the 16+fisheye and, to be honest, never had a huge problem with corner sharpness - not because the corners were sharp, I just didn't notice that they weren't. But since I've been doing a few workshops and rubbing shoulders with the pro crowd more, and entering competitions, I have been more sensitive to the issue. I still don't think it's severe enough to stop me using the lens - as you say, stopping down helps (who needs shallow DoF with wide angle anyway?), but I haven't done detailed testing, so don't take my word for it.
What is your favourite lens for Sony A6500 if you are shooting wide angle? Macro? and fish portrait?
I heard the Sony 16mm with fisheye converter is not good in terms of corner sharpness, what about stopping down the aperture?
For my a6500 I do want to look at the alternatives, and that's why I'm splashing out on the Tokky 10-17 for my forthcoming Socorro trip. But it will have cost me over £2,000 for lens, converter and Zen dome. TF my wife doesn't read WetPixel (I hope).
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