What's a good flash for NEX 7

For powerful and very capable flashes, look for Minolta 3600 or 5600. They can be bought used for respectively under $100 and $200. The 5600 was rebadged as HVL-F56AM, very big and powerful. I have the 3600. Works perfectly with HSS and zoom.

If you're looking for a more compact flash, then yes get the F20AM. It's good enough for most occasions but very limited in functionality.

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