What are uses for lens focal points?

In summary, focal points on a lens are important for various measurements, such as determining magnification and numerical aperture. They also help in producing a parallel beam of light by placing the light source at the focal point. While the focal point itself may not have much use, the location of the focal planes can provide valuable information about the lens. There is a common misconception about the focal distance and working distance, but this is not true. The object distance is typically measured from an imaginary point between two lenses, but it can also be measured from the center of either lens.
  • #1
mkbh_10
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Can you tell me the need & use of the pocal points on a lens , why do we need to have them , why do we measure them .

focal points can be used for various measurements but other than that ?
 
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  • #2
A focal point is not much use at all, since it is not a constant point... maybe useful for burning ants, but that's about it. The location of the focal *planes*, however, are of use- they give you an idea of the magnification of an object, for example. They also help determine the numerical aperture, which sets the resolving power of the lens.

All lenses/lens systems have 6 planes of interest: 2 focal planes, 2 pupil planes, and 2 nodal planes. The optical field at the pupil and focal planes are related via a Fourier transform. Telecentric lenses place one or both of the pupil planes at infinity.

One common misconception I see is that the focal distance is confused with the working distance- that is, the assumption is made that a lens with a 200 mm front focal length needs to be 200 mm from an object to correctly focus it.
 
  • #3
Would u please clear that misconception that u have stated , if the object is placed at the focal point of a convex lens then image is formed at infinity & if the object at infinity is focused then it will come to focus at focal point of a lens
 
  • #5
Question related to combination of two convex lenses ?

The object distance (u) is measured from an imaginary point b/w the two lenses , why so , it does not exist in reality but we use it to find out (V) .

If the object distance is measured from the center of 1st lens or 2nd lens ,will it make any difference ?
 
  • #6
I didnt get u ?
 
  • #7
mkbh_10 said:
Can you tell me the need & use of the pocal points on a lens , why do we need to have them , why do we measure them .

focal points can be used for various measurements but other than that ?

One application is if you want to produce a "parallel beam" with a small bulb.
How do you do this? You put the bulb at the focal point of the lens. Have a look at http://kottan-labs.bgsu.edu/teaching/workshop2001/chapter2_files/image040.gif . This is also called "collimating" the light from the bulb.
 
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1. What is a focal point?

A focal point is a specific point in space or on an object where the majority of light rays converge or diverge. It is the point at which an image is formed, either on a screen or on the retina of the eye.

2. How is a focal point determined?

A focal point is determined by the curvature of the lens or mirror and the distance between the object and the lens or mirror. It is also affected by the wavelength of light and the refractive index of the medium through which the light is passing.

3. Why are focal points important?

Focal points are important because they allow us to create clear and sharp images. Without a focal point, images would appear blurry and distorted. Focal points also play a crucial role in various optical devices, such as cameras and telescopes.

4. Can focal points be changed?

Yes, focal points can be changed by altering the distance between the object and the lens or mirror. This can be done manually in devices like cameras, or automatically in devices like eyeglasses with adjustable lenses.

5. What happens if an object is placed at a focal point?

If an object is placed at a focal point, the light rays from that object will be parallel to each other after passing through the lens or mirror. This means that they will not converge or diverge, resulting in a blurred image or no image at all.

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