I once had an Incase snap case for my iPhone 4. It came with a feature call flash ring. Which is just a black ring (rubber?) fitted around the hole exposing the camera and flash. I didn’t think at that time that Incase was keeping it real. Later on when I tried a generic snap case (this one made of blue plastic and no flash ring), I realize Incase wasn’t kidding. All pictures taken with flash had a halo of bluish haze around the border. The darker the subject the worse the haze. Apparently, the flash bounces off the rim of the case and reflected into the camera causing all sorts of trouble. I replace the generic case with my Incase and experimented with the same scene and there was no hazing or so little I didn’t notice. Strangely enough, Incase no longer trumpets this feature on its website. Maybe other manufacturers have caught on and it is no longer a competitive advantage. Still credit is to be given where it is due. The classic Incase snap case for iPhone 4/4S available from Amazon in Clear, Clear Frost or Black Frost.
