# Lenses and missing reflection

I am wondering why reflected rays are not considered with lenses. If a ray strikes a surface, another is reflected off that striking point; however, this is not added when studying lenses, only refracted rays are considered.

Is there any law which gives the ratio of reflected and refracted rays with lenses?

• search for "camera lens reflection" and you will see that there is reflection. Commented Feb 19 at 5:46
• Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
– Community Bot
Commented Feb 19 at 6:06

The ratio of power reflected from an interface to the power incident is called reflectance. For a smooth (as in not rough) interface, it can be calculated using the Fresnel equations. For a ray normally incident on a lens surface from air (or vacuum), it is given by $$R_\text{normal} = \left(\frac{n - 1}{n + 1}\right)^2$$ where $$n$$ is the refractive index of the material the lens is made of. For a glass lens with $$n = 1.5$$, $$R_\text{normal} = 4\%$$.