Cylindrical Mirror

1. Focal length (f)

Positive and negative conditions: For the converging cylindrical mirror (concave cylindrical mirror), the focal length is negative; for the diverging cylindrical mirror (convex cylindrical mirror), the focal length is positive.

Function: The focal length determines the focusing or diverging ability of the cylindrical mirror. The shorter the focal length, the stronger the focusing or diverging effect; the longer the focal length, the weaker the effect on light.

Unit: It is usually meters (m), centimeters (cm), or millimeters (mm).

2. Radius of curvature ®

Relationship with focal length: Under the thin - lens approximation, there is a formula f=\frac{R}{2}f= 2R.

Function: The smaller the radius of curvature, the more curved the surface of the cylindrical mirror is, and the stronger the refraction effect on light; the larger the radius of curvature, the closer the surface of the cylindrical mirror is to a plane, and the weaker the refraction effect on light.

3. Cylinder power (diopter)

Representation method: On the optometrist’s report, “ - ” or “ + ” is often used to represent the concave or convex cylindrical mirror, followed by a numerical value and “DC” to indicate the cylinder power, in units of diopters (D). For example, “ - 1.50 DC” represents a concave cylindrical mirror with a power of 1.50.

Function: The higher the power, the stronger the refraction effect on light in a certain direction, and the greater the bending degree of light.

4. Axis

Function: It is extremely important in correcting astigmatism because the direction of astigmatism may vary from person to person. Only when the axis is adjusted accurately, can astigmatism be effectively corrected.

5. Aperture (D)

Function: The larger the aperture, the larger the field of view that the lens can cover. However, at the same time, the weight and volume of the lens may also increase, so it needs to be considered comprehensively in practical applications.

Unit: Millimeters (mm) or centimeters (cm).

6. Material refractive index (n)

Function: Different materials have different refractive indices. The higher the refractive index, the greater the degree of light deviation when passing through the cylindrical mirror. The refractive index of the material also affects parameters such as the focal length of the cylindrical mirror, and it is an important factor to consider in the design and selection of cylindrical mirrors.

7. Surface accuracy

Function: High surface accuracy can reduce light scattering and distortion, and improve image quality. If the surface accuracy is poor, light may undergo irregular refraction and reflection, leading to problems such as blurred imaging and ghosting.