I mentioned the changing of the binoculars mod, but it turned out that I couldn’t implement the ideas, because of the limitation of minetest engine.
I chose this description:
You only can see farther when you’re holding the binocular and use it. You must hold it on your hand.
+ Wield the binocular by using it, un-wield it when you use it again.
The problem is that:
+ The original fov couldn’t be got. (can be now)
+ The first-view person and third-view person couldn’t be changed.
* There’s no customization for the key configuration.
Hopefully those problems can be solved in the up-coming releases of minetest engine.