Optics 101: Understanding Your Binoculars
May 30, 2022
How to see faraway things more clearly? The first idea that comes to your mind can be the telescope, which is an amazing device that can make the distant objects appear closer. But how does the telescope works? Let’s find out together.
Imagine that if you had a “bigger eye”, you could collect more light from the object and create a brighter image, and then you could magnify part of that image so it stretches out over more pixels on your retina.
Two pieces in a telescope make this possible:
- The objective lens collects lots of light from a distant object and brings that light, or image, to a point or focus, and determines the shortest amplification distance.
- An eyepiece lens takes the bright light from the focus of the objective lens or primary mirror and "spreads it out" (magnifies it) to take up a large portion of the retina, and it determines the sharpness of the image edges.
Of course, only seeing the image is the most basic thing. If you want to see a clearer and more realistic image, you also need to understand the following few things.
- The dielectric film.
When the light hits the normal telescope glass surface, it cannot reflect light completely, 4-5% of the light is lost by the reflection of the glass surface. While adding the dielectric film ensures full reflection and increases the light passing rate, in which way will reduce the loss of reflected light and make the image look more real.
- The phase film.
After the light hits the glass, it will be reflected twice in a row and form a 90 °phase difference from the original image, resulting in a decrease in resolution rate. The phase film ensures that the refraction of different spectra does not shift, making the image clearer.
- The light transmittance.
It is the measurement of visible light passing through a piece of glass, the higher the transmittance, the clearer and more realistic the image will be. Remember that lens material and coating jointly determine the light transmittance.