How do I go into first person aim with bow?

ok if you are using the bow in your right press ( V ) to get it out in your hand and ( C ) for left handed

then press ( SHIFT ) it will start holding it with tow hand and if you press it again you will change it into
FPS mode .

but keep in mind that the heavy bow ( not bow it kind of like a gun ) can't get into FPS mode

and if your using gamepad press LB (XBOX CONT ) ot L1( PS3 CONT )