This what I would call a Grand Bascinet or Battle Helm
This style of Helm was from around the period of 1450 so was worn from the end of the Hundred Years War with France and just before the War of Roses kicked off.
Made by the great armourer David Hewitt of White Rose Armory in his early learning years, his stuff is full on museum quality today.
I have no picture of me in my full armour wearing this helmet, last worn in battle I believe at a re-enactment of Jack Cades rebellion in 1450 or 1990 in the real world.
The helmet is designed to fix firmly to the back and breast plate, it offers no head movement other the limited movement from space inside the helmet, I found this not my cup of tea for foot combat while you feel pretty invulnerable, you need to be constantly twisting your shoulders to see what is behind you and this effect good balance and your fighting stance, I much prefer a beaver and sallet.
The helmet hinges apart for access as can be seen above.
Vision is not bad actually you mainly see through the vent holes.
