Light is simply radiation. This radiation, or rays, consists of waves of varying lengths. The length is the distance between the beginning of the first wave and the beginning of the second wave. . .not unlike a wave on the ocean.
The human eye can perceive light rays between roughly 400 and 800 nanometers in length (one nanometer [nm] = one-millionth of a millimeter). The brain interprets the different wave lengths as colors. For example, blue-violet is in the 400 nm range, extending through blue, green, yellow, orange and finally red at 800 nm.
Oddly enough, the sum total of all the visible wavelengths, seen as daylight, is white. When light strikes a colored object, the object itself filters out certain wavelengths, and we perceive that object in color by the wavelengths that remain. This has definite implications for the hunter and the scope maker both. The human retina has three different types of light-perceiving cells; one for blue-violet, one for green and one for purple. Our blue-violet cells are the most sensitive.
Thus, at twilight, blue objects are seen as brighter than red objects. It is critical that the coatings used on a scope's lenses increase the transmission of all available blue light to give us the best chance of seeing what we're looking at. A good scope will transmit blue light as a neutral image, giving our blue-violet cells every possible opportunity to discern what we are seeing.
To complicate matters, completely different types of cells in our eyes—called "rods"— are responsible for black and white vision ("cones" handle the color). Rods are far more sensitive than cones. So, when we're trying to discern an animal at dusk, or even after dark, we may not see it in color, but we can see it reasonably well in black and white. That's why the transmission of blue light as a neutral image is so important.
Since 1957, we at Schmidt & Bender have studied light—and studied how it affects the hunter. Anyone can make a glorified magnifying glass and call it a riflescope. To create a sophisticated instrument that lets you truly see the light is another story altogether.
It is impossible for any scope to "gather" light. It can only transmit existing light. And, regardless of advertising claims you may have heard, there is no riflescope made that can transmit 100% of available light.
As light enters the objective end of the scope, before it reaches your eye it passes through several lenses. Each lens absorbs a small quantity of light. Residual reflection from the individual lenses will also prevent a certain amount of light from passing through the scope. In addition, undesired reflections within the metal tube can hinder the quality of the viewed image and the transmission of light.
Each lens has two surfaces. Thus, the total number of lenses within a scope (a variable-power scope can have between seven and ten) is multiplied by two, then multiplied by 0.25% to determine the amount of light lost in the transmission. Simple multiplication is not accurate, however, as each succeeding lens progressively reduces the total amount of transmitted light. It is a favorite technique of some scope manufacturers to claim light transmission values of nearly 100%. Of course, they're measuring the first objective lens only, conveniently forgetting about the other eight or nine!
Any higher transmission levels are physically impossible to achieve with current technology, and claims to the contrary are to be discounted. What does light transmission mean in practical terms? An average scope may transmit 85% or so, and inferior scopes substantially less. The human eye can distinguish transmission differences of 3% or more. Consequently, there is a very real difference in what you can see through a superior scope versus run-of-the-mill optics.
The very best rifle scopes human beings can create will transmit to your eye—under perfect conditions—a maximum of 94.5% to 95% of available light. There are but a handful of scope companies remaining that produce optics approaching these levels, Schmidt & Bender being one of them.
Under hunting conditions, when you might be trying to distinguish a target at absolute last light, these differences can be critical. It can determine whether you bag your game or whether you have long since called it a day.
The quality of the coatings utilized on rifle scope lenses (and the skill of the company applying them) are one of the most critical factors in determining the light transmission properties and low light performance of a scope. Good modern coatings are known as "broad band" coatings because they transmit a broad range of the visible light spectrum (i.e., 350 to 780 nm) with a high degree of efficiency. The weighting and mixture of different values of visible light are calculated as "day value" and "twilight value."
Lens coatings are carefully guarded secrets, formulated by skilled physicists. We calculate the makeup of our coatings in direct relation to the physical composition of the glass to which it is applied, since glass can react in differing ways to the same coating. Our coatings are weighted in favor of certain nanometer (color) values, giving preference to certain wave lengths which are most beneficial to the hunter under actual field conditions (see "what is light").
A simple test that will help you determine the quality of a scope's lens coatings is to look into the front objective lens as you would with a mirror. You should not see yourself. If you do see your reflection, it indicates that light is being reflected back instead of passing through the scope.
The glass usedin the lenses of a riflescope also has a dramatic effect on the clarity of the image you see.
Some manufacturers purchase their raw glass from several sources, making for differences in consistency and quality from batch to batch. At Schmidt & Bender, we are so concerned about the quality of our glass, that several years ago we purchased the optical company that for decades has made our lenses, thus ensuring consistent, accurate quality of all our glass.
Some glass can have a yellow or grey cast, often the case with lenses used in scopes of lesser quality. We use only glass specified as "Quality Level 2," normally specified exclusively for the finest camera and microscope lenses.
Each lens has to be milled, ground and polished. The more precise the tolerances and the more skill possessed by the lensmaker, the better the finished product. The lenses found in Schmidt & Bender scopes are made to specifications as demanding and exacting as those used in virtually any optics application in the world.
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