A plane perpendicular to the axis of an optical system and passing through the focal poit of the system
A point of convergence and divergnce of light and other radiations
Focus (only at the focal point if the incoming rays are all parallel to the axis).
By definition: "The secondary focal point is where rays that are parallel when they enter the lens cross or appear to have crossed."
Light travelling through a concave lens will spread out. In most optical systems that use a concave lens, such as a telescope that needs to magnify the focal plane image, this is a desirable effect.
When light rays travel parallel to the optical axis and pass through a convex lens, they converge at a focal point on the opposite side of the lens. This is due to the convex shape of the lens causing the light rays to refract towards the center of the lens. The point at which the light rays converge is known as the focal point, and the distance between the lens and the focal point is called the focal length. This phenomenon is governed by the lens equation, which relates the object distance, image distance, and focal length of the lens.
Focal length is related to the lens. It has nothing to do with how near or far the object is to the lens or objective.
focal length of the lens
The distance from a lens to the focal point is called the focal length.
A converging lens, such as a convex lens, has a focal point where parallel rays of light converge after passing through the lens. This focal point is where the image of an object placed at infinity will be formed.
The focal point is the point where light converges after it passes through a concave lens. The focal length is the distance of the focal point to the lens. Same for a convex lens, except that the focal point is the imaginary point from where light deflected from lens seems to have emerged.
When the curvature of a lens is larger, the focal point moves closer to the lens. This means the lens has a shorter focal length and will converge light rays at a point closer to the lens.
A focal point in a convex lens is the point where parallel rays of light converge after passing through the lens. It is located on the principal axis of the lens at a specific distance from the lens center, known as the focal length. This focal point is where an image is formed when an object is placed at an appropriate distance from the lens.
The distance from the centre of the lens to the focal point.
The focal point of a concave lens is located on the same side as the incoming light. It is a virtual focal point, meaning the light appears to diverge from this point when passing through the lens.
In a concave lens, the focal point is located on the same side as the incoming light rays. A more curved concave lens will have a shorter focal length, bringing the focal point closer to the lens surface.
If you shine a parallel (ie unfocussed) beam of light perpendicular to a convex lens it will focus to a point on the other side. That place is called the focal point of the lens. Its distance to the lens is called the focal length.
When light rays pass through a convex lens, they converge to a focal point, creating a real and inverted image. The size and position of the image depend on the distance of the object from the lens and the focal length of the lens.
It is easier to find the focal point of a convex lens because the focal point is on the same side as the incoming light, making it more accessible to measure. In contrast, for a concave lens, the focal point is behind the lens and is virtual, making it harder to locate experimentally.