Q: When it is within one focal length from the lens?

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A converging lens is a simple magnifying glass when the object is within one focal length of the lens. The image is then virtual, magnified, and right-side up.

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If an object lies within the focal length of a convex lens, its image will be erect, bigger in size and virtual. It will be on the same side of the object.

It means that if you combine two or more lenses (one after the other), the effect (for many purposes) would be similar to a single lens that has such-and-such properties.

-- The distance from the center of the lens to the plane in which the rays converge is the 'focal length' of the lens. -- If the rays emanated from one point on an object, then rays from all the other points on the object do the same thing, and a real image is formed.

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The distance from the center of a lens to one of its focal points is the focal length of the lens.

A zoom lens you can go from one focal length to another such as 70-200mm and a fixed is one focal length such as 50mm

there can be two ways to cut a convex lens into two equal parts-- one, along the principal axis and another, perpendicular to the principal axis. If the lens is cut along the principal axis, then there will bo NO change in the focal length of the lens. But, if it is cut perpendicular to the principal axis, then the focal length will be twice the original one.

A converging lens is a simple magnifying glass when the object is within one focal length of the lens. The image is then virtual, magnified, and right-side up.

The one with the largest available focal length.

A Prime lens is one that a fixed focal length. An example would be a 35mm lens. Prime lenses tend to have higher aperture capabilities at a lower cost. They also tend to focus faster because the focal length never changes.

MM refers to the focal length of the lens. In the old, old days of Paul Rudolph's original Tessar lens, "focal length" meant the distance between the middle of the lens and the "focal point" - the point at which all the rays of light coming out of the lens converge on one spot. That lens was first introduced in 1902, and since then we've learned that different focal lengths of lenses have different angles of view...so now, if a lens has an angle of view equal to that of a 50mm lens, we call the lens a "50mm" regardless of the actual length of the lens.

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That number is the focal length of the camera's lens ... which focuses light from the scene to form an image on the 'film' or CCD inside the camera. The longer the focal length of the lens, the larger (nearer) the objects appear to be in the picture. (One radian of angle as seen by the lens ===> One focal length on the film.) On the cameras described in the question, the focal length is given as a range ... "from 18 to 200 mm", and "from 55 to 200 mm". Each of these is a "zoom" lens, whose focal length can be changed over the range, enabling the user to cause objects in the picture to appear somewhat nearer or farther away.

For visual observation: Magnification = (Focal Length of Objective Lens) divided by (Focal Length of Eyepiece) (They have to be measured in the same units.) For prime-focus photography: (One focal-length of the Objective Lens on the film) = (one radian in the sky)

The formula for focal length is given byÊ1 divided by 1/a plus 1/b, where 'a' is the distance to a lamp or light source and 'b' is the distance to the wall. You find the focal length by placing a lens parallel to a white wall and focus a light source through the lens until one gets a clear image. The lamp has to be positioned so that it is close to the optical axis of the lens.

The magnification (MA) equals the focal length of the objective lens (fo) divided by the focal length of the eyepiece (fe), which is this: MA = fo / fe = 10 feet / .25 inches = 120 inches / .25 inches = 480 A link to the Wikipedia article on magnification is included.