This is great!
Just to back up what Hitman said, both British and American reports on the captured U-570 show that 1.5x and 6x are the correct magnifications for both periscopes.
http://www.uboatarchive.net/U-570.htm
American periscopes were also set up the same way.
http://www.maritime.org/doc/fleetsub/pscope/index.htm
I'm looking forward to trying this out.
