Optical system with a medium different from air

In summary, the conversation discussed an optical system consisting of a circular LED source, a smaller circular diaphragm, a smaller lens, and a CMOS sensor. The image is optically after the focal plane, but practically it will lie on it due to the sensor. The group then discussed the effects of inserting an empty cuvette and filling it with water on the light spot seen on the sensor. The conclusion was that the spot widens when light passes through water, which was initially thought to be due to double refraction but was actually due to the index of refraction of water being greater than air.
  • #1
Frank-95
52
1
Hi all!

I have an optical system made up like this:

Circular led source -> smaller circular diaphragm -> circular even smaller lens -> cmos sensor at the posterior focal plane

This is the in scale model:
AAA.png


The image is optically after the focal plane, but practically it will lie on it due to the sensor.

Now what happens is this.
Firstly I insert an empty cuvette between the led and the diaphragm. The cuvette fills completely the gap, and is 12mm and it is made by 1 mm of plastic per side.

What I see upon the sensor is the same light spot, attenuated though. This means that the real part of the plastic refraction index, and/or the small plastic width light has to pass through, is not high enough to see size changes in the spot. The imaginary part is, though, since I can see an attenuation.

Then I fill the cuvette with water, so that I have 1 mm plastic, 10 mm water, 1 mm plastic. What I see in the sensor is a visible widening of the spot.
At first I thought it was because of double refraction rays movement, but then I realize that since water index is greater than air one, rays should focus better than air so the spot should be smaller.

Why does the light spot broads when the light passes though water?

Thank you very much.
 
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  • #2
Why do you say that greater index of refraction should focus better? It depends on the focal point of the lens.
 

Related to Optical system with a medium different from air

1. What is an optical system with a medium different from air?

An optical system with a medium different from air refers to any system that utilizes a material other than air to manipulate light. This can include materials such as water, glass, or other transparent substances.

2. How does the presence of a medium other than air affect light propagation in an optical system?

The presence of a medium other than air can affect light propagation in several ways. For example, the speed of light may change as it travels through the medium, causing refraction. The medium may also absorb some wavelengths of light, resulting in color distortion.

3. What are some common examples of optical systems with a medium different from air?

Some common examples of optical systems with a medium different from air include lenses, prisms, and fiber optic cables. These systems use materials such as glass or plastic to manipulate and transmit light for various purposes.

4. How does the refractive index of a medium affect the behavior of light in an optical system?

The refractive index of a medium determines how much the speed of light will change as it travels through the material. This affects the angle at which light is bent, and ultimately, how the image is formed in an optical system.

5. What are some advantages of using a medium other than air in an optical system?

Using a medium other than air in an optical system can offer several advantages. For example, it can allow for more precise control of light, as well as the ability to manipulate different wavelengths of light. Additionally, some materials may be more resistant to environmental factors such as temperature and humidity, making them more reliable for certain applications.

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