Just like all of Olloclip’s older attachable lenses, the Active is a double-ended accessory that you slip onto your iPhone with the aid of a non-included phone case. While you don’t need the special Olloclip case in order to perfectly line up the lenses with the iPhone’s camera, the added shell helps keep the Active firmly attached to the handset.

The case itself is nice enough, a tinted polycarbonate shell that still lets you see your phone while adding a protective and grippy rubber bumper around the edge. Most of your phone will be safely encased, bear in mind there’s a large window left open around the camera lens to accommodate the Active.
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https://www.techradar.com/reviews/phones/mobile-phone-accessories/olloclip-active-1302346/review