Can you still fit the gopro in the waterproof case with an aftermarket lens? I use mine for both scuba and multicoptery.
You want the one from OSTRC. It's the same lens as Ragecams. You will have to make sure you pack in some material around the lens barrel as the sensor is somewhat exposed after the swap. I used o-rings. Also, focus will be a pita, but the nice part is you can set some marks on the lens and refocus it as needed. You may not always want it at infinity.
Finally, be prepared to have any shot that's even remotely in to the sun ruined by lens flare and nasty reflection. It's not the kind that adds to the image.. it makes it unusable. And as an added bonus, the effects of jello are greatly enhanced due to the narrower FOV. Balanced props and shooting in lower light are important.
I've done three of these conversions with the exact same results. But it's well worth it in certain cases. You will want a OEM lens GoPro to have as well. The modified camera does not fit into the waterproof case without removing some of the cushion material.
YMMV.
