Object Needle
Category : physics
Product Detail
An Object Needle (also referred to as an Optical Pin or Locating Pin) is a precision-pointed metal rod used as a reference target in optics experiments. It serves as the "Object" whose image is tracked through lenses or mirrors to determine focal lengths and refractive indices.
Primary Function: To act as a physical marker in ray-tracing and parallax experiments. In an optical bench setup, one needle serves as the Object, while a second needle (the Image Needle) is used to locate the position of the formed image by eliminating parallax.
The Concept of Parallax: This is the most critical use of the needle. When the image of the first needle and the physical second needle are perfectly aligned, they will move together when the observer's head moves side-to-side. If they are at different distances, they will appear to move relative to each other.
Design & Construction:
The Needle: A hardened steel or brass pin, typically 75mm to 100mm long, tapered to a sharp point at the top.
Mounting Stem: The needle is fixed into a sturdier vertical rod (usually 10mm diameter) that fits into the carriages of an optical bench.
Adjustability: Many laboratory needles are mounted on a small sliding collar with a thumbscrew, allowing the user to adjust the vertical height of the tip so it aligns perfectly with the principal axis of the lens or mirror.
