Editing Optical microscope (section)

==Components==
[[File:Optical microscope nikon alphaphot.jpg|thumb|right|300px|Basic optical transmission microscope elements (1990s)]]

All modern optical microscopes designed for viewing samples by transmitted light share the same basic components of the light path. In addition, the vast majority of microscopes have the same 'structural' components<ref>{{Cite web|title=How to Use a Compound Microscope|url=https://www.microscope.com/education-center/how-to-guides/how-to-use-a-compound-microscope/|access-date=2023-02-08|website=Microscope.com|language=en}}</ref> (numbered below according to the image on the right):{{cn|date=December 2024}}
* [[Eyepiece]] (ocular lens) (1)
* Objective turret, revolver, or revolving nose piece (to hold multiple objective lenses) (2)
* [[objective (optics)|Objective lenses]] (3)
* Focus knobs (to move the stage)
** Coarse adjustment (4)
** Fine adjustment (5)
* Stage (to hold the specimen) (6)
* Light source (a [[light]] or a [[mirror]]) (7)
* Diaphragm and [[condenser (microscope)|condenser]] (8)
* Mechanical stage (9)

===Eyepiece (ocular lens)===
{{Main|Eyepiece}}

The [[eyepiece]], or ocular lens, is a cylinder containing two or more lenses; its function is to bring the image into focus for the eye. The eyepiece is inserted into the top end of the body tube. Eyepieces are interchangeable and many different eyepieces can be inserted with different degrees of magnification. Typical magnification values for eyepieces include 5×, 10× (the most common), 15× and 20×. In some high performance microscopes, the optical configuration of the objective lens and eyepiece are matched to give the best possible optical performance. This occurs most commonly with [[apochromat]]ic objectives.{{cn|date=December 2024}}

===Objective turret (revolver or revolving nose piece)===
Objective turret, revolver, or revolving nose piece is the part that holds the set of objective lenses. It allows the user to switch between objective lenses.{{cn|date=December 2024}}

===Objective lens===
{{Main|Objective (optics)}}

At the lower end of a typical compound optical microscope, there are one or more [[objective lens]]es that collect light from the sample. The objective is usually in a cylinder housing containing a glass single or multi-element compound lens. Typically there will be around three objective lenses screwed into a circular nose piece which may be rotated to select the required objective lens. These arrangements are designed to be [[Parfocal lens|parfocal]], which means that when one changes from one lens to another on a microscope, the sample stays in [[focus (optics)|focus]]. Microscope objectives are characterized by two parameters, namely, [[magnification]] and [[numerical aperture]]. The former typically ranges from 5× to 100× while the latter ranges from 0.14 to 0.7, corresponding to [[focal length]]s of about 40 to 2&nbsp;mm, respectively. Objective lenses with higher magnifications normally have a higher numerical aperture and a shorter [[depth of field]] in the resulting image. Some high performance objective lenses may require matched eyepieces to deliver the best optical performance.{{cn|date=December 2024}}

====Oil immersion objective====
[[File:Leica EpifluorescenceMicroscope ObjectiveLens.jpg|thumb|right|300px|Two Leica [[oil immersion]] microscope objective lenses: 100× (left) and 40× (right)]]
{{Main|Oil immersion}}

Some microscopes make use of [[oil-immersion objective]]s or water-immersion objectives for greater resolution at high magnification. These are used with [[index-matching material]] such as [[immersion oil]] or water and a matched cover slip between the objective lens and the sample. The refractive index of the index-matching material is higher than air allowing the objective lens to have a larger numerical aperture (greater than 1) so that the light is transmitted from the specimen to the outer face of the objective lens with minimal refraction. Numerical apertures as high as 1.6 can be achieved.<ref>{{cite web |url=http://www.olympusmicro.com/primer/anatomy/objectives.html |title=Microscope objectives |work=Olympus Microscopy Resource Center |first=Spring |last=Kenneth |author2=Keller, H. Ernst |author3=Davidson, Michael W. |access-date=29 October 2008 |url-status=live |archive-url=https://web.archive.org/web/20081101133539/http://www.olympusmicro.com/primer/anatomy/objectives.html |archive-date=1 November 2008  }}</ref> The larger numerical aperture allows collection of more light making detailed observation of smaller details possible. An oil immersion lens usually has a magnification of 40 to 100×.{{cn|date=December 2024}}

===Focus knobs===
Adjustment knobs move the stage up and down with separate adjustment for coarse and fine focusing. The same controls enable the microscope to adjust to specimens of different thickness. In older designs of microscopes, the focus adjustment wheels move the microscope tube up or down relative to the stand and had a fixed stage.{{cn|date=December 2024}}

===Frame===
The whole of the optical assembly is traditionally attached to a rigid arm, which in turn is attached to a robust U-shaped foot to provide the necessary rigidity. The arm angle may be adjustable to allow the viewing angle to be adjusted.{{cn|date=December 2024}}

The frame provides a mounting point for various microscope controls. Normally this will include controls for focusing, typically a large knurled wheel to adjust coarse focus, together with a smaller knurled wheel to control fine focus. Other features may be lamp controls and/or controls for adjusting the condenser.{{cn|date=December 2024}}

===Stage===
The stage is a platform below the objective lens which supports the specimen being viewed. In the center of the stage is a hole through which light passes to illuminate the specimen. The stage usually has arms to hold [[Microscope slide|slides]] (rectangular glass plates with typical dimensions of 25×75&nbsp;mm, on which the specimen is mounted).{{cn|date=December 2024}}

At magnifications higher than 100× moving a slide by hand is not practical. A mechanical stage, typical of medium and higher priced microscopes, allows tiny movements of the slide via control knobs that reposition the sample/slide as desired. If a microscope did not originally have a mechanical stage it may be possible to add one.{{cn|date=December 2024}}

All stages move up and down for focus. With a mechanical stage slides move on two horizontal axes for positioning the specimen to examine specimen details.{{cn|date=December 2024}}

Focusing starts at lower magnification in order to center the specimen by the user on the stage. Moving to a higher magnification requires the stage to be moved higher vertically for re-focus at the higher magnification and may also require slight horizontal specimen position adjustment. Horizontal specimen position adjustments are the reason for having a mechanical stage.{{cn|date=December 2024}}

Due to the difficulty in preparing specimens and mounting them on slides, for children it is best to begin with prepared slides that are centered and focus easily regardless of the focus level used.{{cn|date=December 2024}}

===Light source===
Many sources of light can be used. At its simplest, daylight is directed via a [[mirror]]. Most microscopes, however, have their own adjustable and controllable light source – often a [[halogen lamp]], although illumination using [[LED]]s and [[laser]]s are becoming a more common provision. [[Köhler illumination]] is often provided on more expensive instruments.{{cn|date=December 2024}}

===Condenser===
The [[condenser (microscope)|condenser]] is a lens designed to focus light from the illumination source onto the sample. The condenser may also include other features, such as a [[diaphragm (optics)|diaphragm]] and/or filters, to manage the quality and intensity of the illumination. For illumination techniques like [[dark field]], [[phase contrast]] and [[differential interference contrast]] microscopy additional optical components must be precisely aligned in the light path.{{cn|date=December 2024}}

===Magnification===
The actual power or [[magnification]] of a compound optical microscope is the product of the powers of the [[eyepiece]] and the objective lens. For example a 10x eyepiece magnification and a 100x objective lens magnification gives a total magnification of 1,000×.  Modified environments such as the use of oil or ultraviolet light can increase the resolution and allow for resolved details at magnifications larger than 1,000x.{{cn|date=December 2024}}