My first experience with Schmidt and Bender scopes was when I transferred from a regular Special Forces A-team to a dedicated sniper team. I couldn't wait to take a stroll through the arms room to see what I'd be getting issued, as many of the guns were not available anywhere else, even in Special Forces.
As I was perusing the soon-to-be-issued hardware, I noticed a handful of scopes unlike any others I had used in the past. Closer inspection revealed that Schmidt and Bender made a few of them. Scopes are one of the areas where some military units are free to experiment and can purchase whatever they choose to take overseas. They are not regulated like issued small arms, which is why we often see a wide variety of optics show up in pictures taken by our servicemen.
Over the course of the next two years spent in uniform and in all the years since, I've always had an appreciation for Schmidt and Bender optics. They're expensive, but they are some of the most popular scopes for the more well-heeled Special Operations units. In these circles, the 5-25x56mm is a prominent feature in the optical landscape. The reason for Schmidt and Bender's popularity is its products' performance.
Optically, the Schmidt and Bender 5-25x56 continues to be the yardstick by which all premium scopes get measured. Ten years ago, there was quite a gap in performance between the Schmidt and Bender 5-25X and everybody else's offerings, but the newest scopes from the competition are so similar, it's hard to tell which is which once you're behind the ocular. Even still, the old 5-25X remains the one to beat just because it's been so good for so long.
The 3-20x50 is one of Schmidt and Bender's newer scopes, and it brings a lot of the 5-25X's DNA into a more updated package. The two scopes are similar is size and weight, the real differences being in magnification range and optical performance.
The 3-20x50mm has a smaller objective lens, giving this model better pure optical performance over the 5-25x56mm. The reason the 3-20X performs better than the 5-25X when set at the same magnification is that the smaller objective lens doesn't have to bend the incoming light as aggressively prior to the focused image reaching the next internal lens. Optical engineers refer to this phenomenon as a scope's "speed."
Fast scopes will have worse image quality when compared with slower scopes made from the same materials. Fast scopes have large objective lenses, high magnification and short overall length. The 3-20x50 has a smaller objective and a touchless magnification, so the pure optical performance is better than the venerable 5-25X. Of course, the extra magnification of the 5-25X will usually make up for the difference in resolution between the two.
The point to remember with the smaller objective lenses is that they will also yield a smaller exit pupil. This means that smaller objective lenses require our head to be more precisely placed behind the scope in order to gain a full field of view. This helps when we're going for maximum precision and hurts when we're trying to shoot fast.
Regardless of which Schmidt and Bender scope can best suit your needs, believe me when I tell you that they are proven optics that have been serving well in elite military units for more than a decade. There's so much history and performance behind the 5-25x56mm that I fully intend on buying one someday. It'll probably be used in order to save a few dollars. However, if money were no object, I'd buy the 3-20x50mm, too.