ORIGINAL: okcmco
I beleive the most important difference is that the 3200 is multi coated and the 4200 is FULLY multi coated. For those who don't know, multi coated means that the lenses surfaces that are coated have multiple coatings. This does not mean that all surfaces are coated. In fact it means that NOT ALL of the surfaces are multicoated.
The 4200 is FULLY MULTI COATED which means all surfaces have multiple coatings. This explains why the 4200 has up to 95% efficiancy as regards light transmission. That is about the brightest on the market and is probably the theoretical limit.
The 4200 is an almost perfect scope. The reason I don't use them is that the eye relief is not very forgiving. But as to image quality the 4200 is exceptional.
okcmco
at my company, we coat lenses for different applications, and once the equipment is set up, it cost pennys to coat. Its expensive to calibrate and get the coatings so it matches the index of air perfectly. But they charge a serious premium for it. The technology has been around for decades, but only being seriously ultilized now.