I have looked over some of the (less expensive) Kowa scopes, like the TSN-601 and TSN-660. The dimensions don't seem very different. What would the functional difference between the two be? 601/602 versus the 660?

Not familiar with these scopes. But a lot of optics manufacturers offer different lines of scopes that are very similar. Most cases you get better quality glass and coatings with the higher priced lines. I would suspect this is the case with these as well.

From what I understand, Kowa is one of the few Japanese companies who actually make their own lens. They build great scopes and binoculars and prices vary depending on the type of glass they use. Their FL and ED lenses are some of - if not the very best in the industry. Even their lower end stuff is very good.

The 660 series has far more features than the 600 series. I owned a 661 or 662, whichever was 45 degree. They are outstanding. The 660 is a smaller(66mm) lighter version of the 82mm series. Most of the eyepieces and accessories for the 820 series fit the 660 series.

The 600 is more of an economy model. I would go for the 660 series. I am getting another soon myself.

I jad a 660 or 661 (can't remember which) and if you were looking through the eyepiece when you turned the focus knob you could see the image jump and hear a loud click at the same time. This would occur close to the middle of the focus range. I sent it back for a refund. Wish I could have afforded one of the higher end models, their glass is awesome.

Steve E.......

I agree with the quality of their glass. I have looked through several models and have been impressed. I also noticed in a documentary about the US Army Sniper School that they use the Kowa 600 series there (even though the Army system issues the Leupold spotters to the field units).