O-flash

A big issue with these things is that a lot of people get low-cost ring-lights that are really just a bunch of LEDs. Some of them are so dim they don't even publish their guide number, or the guide number isn't anything close to the amount of light from a real flash. If you're hoping to do macro shots, then you'll need a lot of light to allow small apertures that give you more DOF, and you want to use real flash with a pretty high guide number.

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Jeremy Birn