also
in the lower end bonos porro prism are the better to get over the roof prism models.
the porro prism models are clear birghter and crisper than the roof prims models that arent phase corrected. but the roof prisms that are phaser correcte are more rugged than the porros and just as good opticaly.
most all roof prism glasses more than 250 and up are phase corrected.
these are what i want but i dont see it happening anytime soon.
http://www.riflescopes.com/products/..._binocular.htm