Hi,
did this topic not made it to these forums?
Fallout 4 obviously has a problem with performance when using scopes.
Some mentioned that this is a flaw by design, when scoping in you have to load more detailed version of the area around you for a lot more range - which causes the frame drop, as per default the game engine does not just forget everything else around you and is still rendered (in case you zoom out again).
Though a lot of games do fine with that (maybe there are some workarounds or tricks to optimize performance for zooming in), some other don't.
But imho Bethesda should do something about that as the performance drop is very severe in FO4!