Chromatic aberration is an optical defect in which light passing through a lens system is partially decomposed into spectral components. This greatly spoils the image when observing through a homemade telescope or a telescope. The subject loses its sharpness and appears iridescent.
It is necessary
- - optical device with chromatic aberration;
- - cardboard;
- - scissors;
- - a set of light filters;
- - measuring instruments;
- - achromatic lens.
Instructions
Step 1
Observe the objects you want through the light filter. Most often, in homemade optical devices there is a simple large-diameter lens. To get rid of the defect, it is necessary to narrow the spectral range. Use ZhS17 or ZhS12 light filters for this. They can be taken from photosets. They are yellow in light. Place them in front of the lens or behind the eyepiece. The first option is preferable, but it depends on the size of the filter and lenses. The image will take on a yellowish tint, but will become sharper. In this way, you can observe bright objects - for example, the moon.
Step 2
Reduce the relative aperture of the optical instrument. The fact is that the larger the lens diameter, the greater the chromatic aberration. But there is a certain ratio between the lens diameter and the focal length, at which it is hardly noticeable. Cut a circle out of cardboard that is the same diameter as the inside diameter of your spotting scope or telescope. In the center of it, make a round hole with a diameter of 1.5-2 times smaller than the diameter of the lens. Paint the resulting diaphragm black. Place it inside the tube a short distance from the lens. Observing through an optical device, select such a distance from the circle to the lens, at which the aberration will be minimal. You can experiment with the diameter of the aperture opening. Here it is necessary to take into account that the farther from the lens the aperture is, the smaller the diameter of the hole should be.
Step 3
The most radical way to combat chromatic aberration is to use achromatic lenses. In the simplest case, such a lens consists of two lenses made of different types of glass. The refractive indices of various spectral components of light are opposite in them, and the total focal length corresponds to that required in an optical device. Such lenses are found in camera lenses, binoculars, theodolites and professional telescopes. Try using a telephoto lens with a long focal length instead of your device lens. Chromatic aberration in such a device should practically not be felt.
Step 4
If possible, replace the lens optical system with a mirrored one. They are used in powerful professional astronomical instruments. If you come across an MTO brand photographic lens, try making a telescope based on it. To do this, you just need to add an eyepiece to it. These lenses are quite common in thrift stores. It is just a mirror-lens system. The device will be practically free from all types of aberrations.
