One of the most important properties of microscope objectives is their magnification. Magnification usually ranges from 4× to 100×. It is combined with the magnification of the eyepiece to determine the total magnification of the microscope; A 4× lens with a 10× eyepiece produces an image 40 times larger than the object. “Objective lens Merriam-Webster.com Dictionary, Merriam-Webster, www.merriam-webster.com/dictionary/objective%20lens. Retrieved 9 December 2022. Instead of finite tube lengths, modern microscopes are often designed to use infinity correction, a technique in microscopy in which light coming out of the lens of the objective is focused to infinity. [1] This is indicated on the lens by the infinity symbol (∞). In addition to oxidized glasses, fluorite lenses are often used in special applications. These fluorite or semi-apochromat lenses adapt better to color than achromatic lenses.
To further reduce aberration, more complex designs such as apochromatic and superachromatic lenses are also used. (usually) epifluorescent light microscopy system in which a fine laser beam is scanned through the object through the lens of the objective. The distinction between lenses designed for use with and without slides is important for large numerical aperture lenses (high magnification), but makes little difference for low magnification lenses. Working distance (sometimes abbreviated WD) is the distance between the sample and the lens. With increasing magnification, working distances usually decrease. If space is needed, special lenses with a large working distance can be used. The traditional thread used to attach the objective to the microscope was standardized by the Royal Microscopical Society in 1858. [3] It was based on the British Whitworth standard with a diameter of 0.8 inches and 36 wires per inch. This “RMS feed” or “company thread” is still used today. Alternatively, some lens manufacturers use designs based on ISO metric screw threads, such as M26 × 0.75 and M25 × 0.75. Camera lenses (usually referred to as “photographic lenses” rather than simply “lenses”[4]) must cover a large focal plane and therefore consist of a series of optical elements to correct optical aberrations.
Image projectors (such as video, film, and slide projectors) use lenses that simply reverse the function of a camera lens, with lenses covering a large image plane and projecting onto another surface at some distance. [5] Some microscopes use an oil- or water-immersion lens, which can have a magnification of more than 100 and a numerical aperture of more than 1. These lenses are specially designed for use with oil or water corresponding to the refractive index, which must fill the space between the front element and the object. These lenses offer higher resolution at high magnification. Digital apertures of up to 1.6 can be achieved with oil immersion. [2] In a telescope, the objective is the lens at the front end of a refractive telescope (e.g., binoculars or telescope) or the primary mirror imaging a mirror or retro-reflecting telescope. The light-gathering power and angular resolution of a telescope are directly related to the diameter (or “aperture”) of its lens or mirror. The larger the target, the brighter the objects appear and the more details can be resolved.
In optical engineering, the lens is the optical element that collects light from the observed object and concentrates the light rays to create a real image. Lenses can be a single lens or mirror, or combinations of several optical elements. They are used in microscopes, binoculars, telescopes, cameras, slide projectors, CD players and many other optical instruments. Lenses are also called object lenses, object glasses or lens glasses. The numerical aperture of microscope lenses is typically between 0.10 and 1.25, which corresponds to focal lengths of about 40 mm to 2 mm. In the past, microscopes were almost universally developed with a finite mechanical tube length, which is the distance that light travels in the microscope from the objective to the eyepiece. The Royal Microscopical Society`s standard is 160 millimeters, while Leitz often used 170 milliliters. 180mm tube length lenses are also quite common. Using an objective and microscope designed for different tube lengths results in spherical aberration. In contrast, so-called “metallurgical” lenses are designed for reflected light and do not use glass slats.
A typical microscope has three or four objective lenses with different magnifications screwed into a circular “nose” that can be rotated to select the desired lens. These lenses are often color-coded to make them easier to use. The least powerful lens is called a scanning lens and is usually a 4× lens. The second lens is called a small lens and is usually a 10× lens. The most powerful of the three lenses is called a large lens and usually measures between 40 and 100×. The objective lens of a microscope is the one located at the bottom near the sample.