Learn About Optic Components & Image Quality

Lenses

No other factor influences image quality more than the lenses in an optic. Numerous conditions determine overall performance, and as the precision and quality of the lenses, coatings, and glass increase, so does the cost. Light interacts with glass surfaces in complex ways, and the goal is to utilize the light entering the optic to produce the brightest and sharpest image possible.

Different colors (or wavelengths) of light pass through lenses and bend at slightly different angles, similar to a prism. Multiple lenses made from various types of glass are required to correctly focus each color in the image. Uncorrected elements lead to blurred images with distortions and muddied colors. Modern optics use specialized glass, such as Extra-low Dispersion (ED), High Density (HD), or fluorite (CaF2) glass, along with sophisticated designs to mitigate these issues.

Mirrors

Mirrors, or prisms, within an optic are as critical as the lenses. Roof prism designs generally include anti-phase shifting coatings to prevent interference issues. Coatings are applied to mirrors to enhance light transmission and prevent scattering. Lower-priced optics often use BK7 prisms, which produce an exit pupil with shaded edges, while higher-quality optics use BAK4 prisms, which produce a round exit pupil, offering better image quality, especially in low-light conditions.

Coatings

Light transmission through a lens can result in reflective loss. Thin coatings on lens surfaces reduce this loss and enhance light transmission. Each lens in a binocular or scope can lose up to 5% of light without coatings. High-quality optics with multi-coatings can reduce this loss to tenths of a percent, significantly improving image brightness and clarity.

Types of Coatings:

• Coated (C) Optics: A thin anti-reflective coating on one or more lens surfaces.
• Fully Coated (FC) Optics: Anti-reflective coatings on both sides of the objective and ocular lens systems and the long side of the prism.
• Multi-coated (MC) Optics: Multiple coatings on one or more lens surfaces. Even some high-quality optics only have a single coating on the outer surface for durability.
• Fully Multi-coated (FMC) Optics: Multiple coatings on all lens surfaces, indicative of top-tier optics design and execution.

Distortions

Modern optics typically present a normal image, though perfect images are nearly impossible to achieve. Curvature of Field is the most common distortion, noticeable when a straight object, like a telephone pole, appears to curve at the edge of the view. Pincushion and barrel distortions are less common, caused by varying magnifications across the field of view, leading to warped shapes.

Aberrations

Aberrations, often interchangeable with distortions, refer to defects that prevent orderly focus, reducing image sharpness and color fidelity. Chromatic aberration is the most common, where different colors focus at different points, leading to muddy fringes and poor contrast. High-density glasses like ED, HD, or SD, reduce these effects, providing better color fidelity and contrast. Coma and spherical aberration are other notable aberrations, affecting sharpness and detail.

Alignment

Proper alignment of optical elements, including mirrors, is crucial for image quality. Misalignments, especially in scopes where distances are greater, can significantly degrade image quality. In binoculars, misalignment between barrels, known as collimation, can cause fatigue, eyestrain, and double images. The hinge connecting the barrels must be precise to maintain proper collimation and prevent alignment issues.

Conclusions

• Lenses: Critical for image quality, with modern materials enhancing color purity and contrast.
• Coatings: Essential for improving light transmission and reducing internal light scatter, crucial for image brightness and clarity.
• Distortions: Less impactful on image quality and increasingly well-controlled in modern optics.
• Aberrations: Typically a combination of intrinsic defects, affecting image quality, contrast, and color fidelity.
• Alignment: Precise and secure alignment of optical elements is vital for optimal performance. Misalignment can severely impact image quality.

By understanding these factors, you can better appreciate the complexities involved in achieving high-quality images and make more informed choices when selecting optics.