What are uses for lens focal points?

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Focal points on a lens are essential for various optical measurements and applications, such as determining magnification and numerical aperture, which affects resolving power. They help in creating parallel beams of light, as placing a light source at the focal point allows for collimation. There is a common misconception that the focal distance equals the working distance, but they are distinct concepts; the focal point does not dictate the distance required for proper focus. Additionally, lenses have multiple planes of interest, including focal, pupil, and nodal planes, which are interconnected through Fourier transforms. Understanding these principles is crucial for effective lens application in optics.
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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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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.
 
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
 
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 ?
 
I didnt get u ?
 
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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