orthocromatic film?

[MrEd31]

I was looking at some photos and I came across some striking images. The caption said that the photographer used agfa ortho 25. I am wondering how orthocromatic film works. What is it used for? I understand that it is insensitive to red light, but why not just use a red filter and pancromatic film? Some help would be appreciated, thanx!

 

[dlc]

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005ZMy