i would think the materials, manufacturing processes and chemistry that goes into quality optics, or anything else, determine the cost.
You may pay more for the high end but you also have a better chance of getting a better product.The less you pay the better chance you have of getting a lesser product. I shy away from products that talk too much of the great warranty. I would rather hear why their product won't need the warranty or what the return rate is. A product with free replacement means it did not cost much to produce. with me a free replacement will be sent down the road. A lifetime warranty just tells me the manufacturer does not have confidence in what they are selling.
As far as a 1500$ scope. An nxs nightforce would be near the top, it may not be the brightest, but the resolution and mechanics will be excellent. a used s&b, or a german zeiss(not the american market zeiss) would be a choice.. i am sure there are others, but i have experience with these.

Last edited by foogle; 08/13/17. Reason: spell
"We are building a dictatorship of relativism which recoqnizes nothing as definitive and whose ultimate goal consists solely of ones own self ego and desires."Cardinal Rathzinger