Go to the following URL, which is Graham Patterson's Mamiya TLR faq.

http://webdisk.berkeley.edu/~grahamp...html#Heading72

In short, the older design is 4 elements in 3 groups, and the new one 5 in 4. It's supposedly sharper, but I have the old 180 chrome lens, and it makes perfectly acceptable 15x15s. It takes a 49mm filter (which you've noticed by now), so it will take a 49mm Pentax lenshood meant for the 105 takumar, if you're looking for a cheap lens shade.