Looking Glass: optics explained

Time Well Spent June 15, 2022

Optical technology is hard to grasp, so the editor seeks clarity

We read all the time about technologies that make this scope better than that, or this binocular brighter than another, but what do all those buzz words really mean? For example, why do I want extra-low dispersion glass and how is a BAK-4 prism going to help me to see my quarry better? In the field of airgun optics there are few companies better qualified to answer these questions than Hawke Sport Optics. They research, design, and have manufactured some of the finest airgun hunting and competition optics you can buy, so their designers are well placed to get to the heart of what all these technologies mean to us in the real world. I’m a great believer that you should buy the best glass you can afford, be it a rifle scope or a pair of binoculars. The old adage that you can’t shoot what you can’t see has proven true in my experience. Many’s the time I’ve stumbled up on a rabbit or squirrel that saw me as I saw it, and lost the chance of an easy shot. Had I known it was there, I could have slowed my approach and held the advantage long enough to make a kill. To understand these things better I contacted Hawke Sport Optics to get their explanation of the technologies.

ED GLASS LENSES

Extra-low-dispersion glass prevents chromatic aberration (colour fringing) because it gives objective lenses an ability to concentrate and direct the wavelengths of light more effectively than standard glass objectives, in turn controlling and minimising aberrations. Usually, the better the aberrations are controlled, the cleaner and brighter

the image will appear.

HAWKE FULLY-MULTI-COATED LENSES

Most Hawke models are fully multicoated, meaning that all glass-to-air surfaces receive multiple layers of anti-reflection coatings. These special coatings are added to the lenses, decreasing the amount of surface reflection loss, and significantly increasing the transmission of light to ensure a bright, clear, and sharp image. Typically, (but dependant on model) material is usually MgF2, AI2O3, ZrO2, and light transmission is about 99.6% or higher.

BAK-4 PRISMS IN BINOCULARS

In most cases, BAK-4 prisms are considered superior to the older and cheaper BK-7 prisms because they have a higher refractive index. The result is less peripheral light being lost through internal reflection.