Spyglass-like Item Help

I want to make a Minecraft mod that adds a Sniper Rifle, and I want to make it so while you hold the Sniper Rifle and crouch, you will zoom inwards and have an overlay that looks similar to the Spyglass.

I basically want to make an item that works like a Spyglass, but only while you are holding it and crouching, and you can still use it as a ranged weapon.

How would I do this, and is it even possible? If so, how would I do it, and if not, what could I do instead?