Step 1: Being careful not to touch the lens, cover the right objective lens (or close your right eye) and turn the central focusing dial until the image seen by the left eye is clear. Step 2: Cover the left lens (or close the left eye) and this time instead of turning the central focusing wheel, turn the diopter adjustment ring (located near the right eyepiece and displayed on the small image in the upper right) until the image is clear. Step 3: Finally look through the binoculars with both eyes until the image is clear and sharp. 

The hotspot can’t be hidden. Yes others can see it. But it’s only there when you turn it on and automatically shuts off after a minute if not in use. It’s turned on by a remote that is included. You need the password to connect. 

Yes, as long as you are in close proximity to the camera 

I don't see why not, remember that the filter goes on the lens, not on the camera. 

Hi, thank you for your appreciation ,this filter just for camera lens , so it couldn't be used on Sandmarc lens, thanks