During benchrest shooting I use spotting scope Praktica Hydan 25-75x90. But leaving rifle to watch target through spotting scope was quite enoying, so I designed and printed an adaptor for my cell phone (currently I use Samsung Galaxy S8).
More details (3D models to print, build comments and some more photos) are here:
https://www.thingiverse.com/thing:4583429
But just for a quick view:
More details (3D models to print, build comments and some more photos) are here:
https://www.thingiverse.com/thing:4583429
But just for a quick view: