You do not have permission to edit this page, for the following reasons:

This IP address has been blocked from editing Wikipedia.
This does not affect your ability to read Wikipedia pages.
Most people who see this message have done nothing wrong. Some kinds of blocks restrict editing from specific service providers or telecom companies in response to recent abuse or vandalism, and can sometimes affect other users who are unrelated to that abuse. Review the information below for assistance if you do not believe that you have done anything wrong.

The IP address or range 44.201.0.0/16 has been blocked (disabled) by ‪ST47‬ for the following reason(s):

The IP address that you are currently using has been blocked because it is believed to be a web host provider. To prevent abuse, web hosts may be blocked from editing Wikipedia.
You will not be able to edit Wikipedia using a web host provider because it hides your IP address, much like a proxy or VPN.
We recommend that you attempt to use another connection to edit. For example, if you use a proxy or VPN to connect to the internet, turn it off when editing Wikipedia. If you edit using a mobile connection, try using a Wi-Fi connection, and vice versa. If you are using a corporate internet connection, switch to a different Wi-Fi network. If you have a Wikipedia account, please log in.
If you do not have any other way to edit Wikipedia, you will need to request an IP block exemption.

How to appeal if you are confident that your connection does not use a web host's IP address:
If you are confident that you are not using a web host, you may appeal this block by adding the following text on your talk page: ((unblock|reason=Caught by a web host block but this host or IP is not a web host. My IP address is _______. Place any further information here. ~~~~)). You must fill in the blank with your IP address for this block to be investigated. Your IP address can be determined here. Alternatively, if you wish to keep your IP address private you can use the unblock ticket request system. There are several reasons you might be editing using the IP address of a web host (such as if you are using VPN software or a business network); please use this method of appeal only if you think your IP address is in fact not a web host.

Administrators: The IP block exemption user right should only be applied to allow users to edit using web host in exceptional circumstances, and they should usually be directed to the functionaries team via email. If you intend to give the IPBE user right, a CheckUser needs to take a look at the account. This can be requested most easily at SPI Quick Checkuser Requests. Unblocking an IP or IP range with this template is highly discouraged without at least contacting the blocking administrator.

This block will expire on 23:54, 31 July 2024.

Even when blocked, you will usually still be able to edit your user talk page, as well as email administrators and other editors.

For information on how to proceed, please read the FAQ for blocked users and the guideline on block appeals. The guide to appealing blocks may also be helpful.

Other useful links: Blocking policy · Help:I have been blocked
Your IP address is in a range that has been blocked on all Wikimedia Foundation wikis. The block was made by ‪AntiCompositeNumber‬. The reason given is Open proxy/Webhost: Visit the FAQ if you are affected .
- Start of block: 13:55, 18 August 2022
- Expiry of block: 13:55, 18 April 2025
Your current IP address is 44.201.28.123. The blocked range is 44.201.0.0/16. Please include all above details in any queries you make. If you believe you were blocked by mistake, you can find additional information and instructions in the No open proxies global policy. Otherwise, to discuss the block please post a request for review on Meta-Wiki. You could also send an email to the stewards VRT queue at stewards@wikimedia.org including all above details.

You can view and copy the source of this page:

((More citations needed|date=December 2023))((Short description|Optical lens))
[[File:Bi telecentric lens.jpg|thumb|Bi-telecentric lens with 208&nbsp;mm diameter front element and a ((nowrap|[[C mount|C-mount]])) camera interface]]
A '''telecentric lens''' is a special [[lens (optics)|optical lens]] (often an [[objective lens]] or a [[camera lens]]) that has its [[entrance pupil|entrance]] or [[exit pupil]], or both, at infinity. The size of images produced by a telecentric lens is insensitive to either the distance between an object being imaged and the lens, or the distance between the image plane and the lens, or both, and such an optical property is called ''telecentricity''. Telecentric lenses are used for precision optical [[two-dimensional]] measurements, reproduction (e.g., [[photolithography]]), and other applications that are sensitive to the image magnification or the [[Angle of incidence (optics)|angle of incidence]] of light.

The simplest way to make a lens telecentric is to put the [[aperture stop]] at one of the lens's [[Focus (optics)|focal point]]s. This allows only rays including the [[chief ray]]s (light rays that pass through the center of the aperture stop), that will be about parallel to the optical axis on the other side of the lens, to pass the optical system for any object point in the [[field of view]]. Commercially available telecentric lenses are often ''compound lenses'' that include multiple lens elements, for improved optical performance. Telecentricity is not a property of the lenses inside the compound lens but is established by the location of the aperture stop in the lens. The aperture stop selects the rays that are passed through the lens and this specific selection is what makes a lens telecentric.

If a lens is not telecentric, it is either [[entocentric lens|entocentric]] or [[hypercentric lens|hypercentric]]. Common lenses are usually entocentric. In particular, a single lens without a separate aperture stop is entocentric. For such a lens the chief ray originating at any point off of the optical axis is never parallel to the optical axis, neither in front of nor behind the lens. A non-telecentric lens exhibits varying [[magnification]] for objects at different distances from the lens. An entocentric lens has a smaller magnification for objects farther away; objects of the same size appear smaller the farther they are away. A hypercentric lens produces larger images the farther the object is away.

A telecentric lens can be ''object-space telecentric'', ''image-space telecentric'', or ''bi-telecentric'' (also ''double-telecentric''). In an object-space telecentric lens the image size does not change with the object distance, and in an image-space telecentric lens the image size does not change with the image-side distance from the lens.

==Object-space telecentric lenses==
[[File:Telezentrische.Abbildung.objektseitig.png|thumb|Object-space telecentric imaging where the aperture is in the back focal plane of the objective. The entrance pupil is located at infinity, and chief rays before the objective are parallel to the optical axis.|330x330px]]
An object-space telecentric lens has the entrance pupil (the image of the lens's aperture stop, formed by optics before it) at infinity and provides an [[orthographic projection]] instead of the [[perspective projection]] in an entocentric lens. Object-space telecentric lenses have a ''working distance''. Objects at this distance are ''in focus'' and imaged sharply onto the image sensor at [[flange focal distance]] in the camera. An object that is closer or farther is [[defocus|out of focus]] and may be blurry but will be the same size regardless of distance.

Telecentric lenses tend to be larger, heavier, and more expensive than normal lenses of similar [[focal length]] and [[f-number]]. This is partly due to the extra components needed to achieve telecentricity, and partly because the first element in an object-space telecentric lens must be at least as large as the largest object to be imaged. The front element in an object-space telecentric lens is often much larger than the camera mount. In contrast to entocentric lenses where lenses are made larger to increase the aperture for increased collection of light or shallower [[depth of field]], a larger diameter (but otherwise similar) object-space telecentric lens is not [[lens speed|faster]] than a smaller lens. Because of their intended applications, telecentric lenses often have higher [[Optical resolution|resolution]] and transmit more light than normal photographic lenses.

Commercial object-space telecentric lenses are often characterized by their magnification, working distance and maximum image circle or image sensor size. A truly telecentric lens has no [[focus ring]] to adjust the position of the focal plane. Some commercial telecentric lenses, however, do feature a focus ring. This can be used to slightly adjust the working distance and magnification while losing a little bit of telecentricity. Sometimes, manufacturers specify a sensor resolution or pixel size to describe the optical quality of the lens and the maximum [[optical resolution]] it can achieve due to the lens's [[Optical aberration|aberrations]].

Because their images have constant magnification and constant viewing angle across the field of view, object-space telecentric lenses are used for [[metrology]] applications, where a [[machine vision]] system must determine the precise size and shape of objects independently from their exact distance and position within the field of view.

In order to optimize the telecentric effect when objects are [[Backlighting (lighting design)|illuminated from behind]], an additional image-space telecentric lens can be used as a ''telecentric (or collimated) illuminator'', which produces a parallel light flow, often from [[Light-emitting diode|LED]] sources.

==Image-space telecentric lenses==
[[File:Telezentrische.Abbildung.bildseitig.png|thumb|Image-space telecentric imaging where the aperture is in the front focal plane of the objective. The exit pupil is located at infinity, and chief rays after the objective are parallel to the optical axis.|330x330px]]
An image-space telecentric lens has the exit pupil (the image of the aperture stop formed by optics after it) at infinity and produces images of the same size regardless of the distance between the lens and the [[photographic film|film]] or [[image sensor]]. This allows the lens to focus light from an object or sample to different distances without changing the size of the image. An image-space telecentric lens is a reversed object-space telecentric lens, and vice versa.

Since the [[Ray (optics)|chief rays]] (light rays that pass through the center of the aperture stop) after an image-space telecentric lens are always parallel to the optical axis, these lenses are often used in applications that are sensitive to the angle of incidence of light. [[Interference filter|Interference-based]] color-selective [[beam splitter]]s or [[Optical filter|filters]] but also [[Fabry–Pérot interferometer]]s are two examples where image-space telecentricity is used. Another example is minimizing [[crosstalk]] between pixels in image sensors and maximizing the [[quantum efficiency]] of a sensor. The [[Four Thirds System]] initially required image-space telecentric lenses, but with the improvement of sensors, the angle of incidence requirement has been relaxed.<ref>((cite web |title=Micro Four-Thirds and Telecentricity |url=https://theonlinephotographer.typepad.com/the_online_photographer/2008/08/micro-four-thir.html))</ref> Since every pixel is illuminated at the same angle by an image-space telecentric lens, they are also used for [[radiometry|radiometric]] and [[color measurement]] applications, where one would need the [[irradiance]] to be the same regardless of the field position.

==Bi-telecentric lenses==
[[File:Telezentrische.Abbildung.beidseitig.png|thumb|Bi-telecentric imaging where the aperture is in the common focal plane of two [[confocal]] lenses.|330x330px]]
In a bi-telecentric (or double-telecentric) lens, both entrance and exit pupil are at infinity. The magnification is constant despite variations of both the distance of the object being observed and the image sensor from the lens, allowing more precise object size measurements than with a mono-telecentric lens (i.e., the measurements being insensitive to placement errors of the object and the image sensor). A bi-telecentric lens is [[Afocal system|afocal]] (a system without focus) as the image of an object at infinity formed by the first part of the lens is [[collimated beam|collimated]] by the second part.

Commercial bi-telecentric lenses are often optimized for very low [[image distortion]] and [[field curvature]] for accurate measurements across the entire field of view at great [[Optical resolution|resolution]]. These lenses often comprise more than 10 elements.

Large and heavy bi-telecentric lenses with many optical elements are commonly used in [[optical lithography]] (that copies a template of an electrical circuit to print or fabricate onto [[semiconductor]] [[Wafer (electronics)|wafers]] for mass semiconductor device production) because small image distortion and placement errors can be critical for manufactured device functionality.<ref>((cite journal |last1=Matsuyama |first1=Tomoyuki |last2=Ohmura |first2=Yasuhiro |last3=Williamson |first3=David M. |editor-first1=Donis G |editor-last1=Flagello |title=The Lithographic Lens: its history and evolution |journal=Proc. SPIE |series=Optical Microlithography XIX |date=2006 |volume=6154 |page=615403 |doi=10.1117/12.656163 |bibcode=2006SPIE.6154...24M |s2cid=7395678 |url=http://www.lithoguru.com/scientist/litho_history/Lithographic_lens_history_and_evolution_Matsuyama_2006.pdf))</ref>

== References ==
((reflist))

[[Category:Optical microscope components]]
[[Category:Photographic lenses]]
[[Category:Machine vision]]

Pages transcluded onto the current version of this page (help):

Telecentric lens (edit)
Template:Ambox (view source) (template editor protected)
Template:Cite journal (view source) (protected)
Template:Cite web (view source) (protected)
Template:Find sources mainspace (view source) (template editor protected)
Template:Main other (view source) (protected)
Template:More citations needed (view source) (template editor protected)
Template:Nowrap (view source) (protected)
Template:Pagetype (view source) (protected)
Template:Reflist (view source) (protected)
Template:Reflist/styles.css (view source) (protected)
Template:SDcat (view source) (protected)
Template:Short description (view source) (protected)
Template:Short description/lowercasecheck (view source) (protected)
Module:Arguments (view source) (protected)
Module:Category handler (view source) (protected)
Module:Category handler/blacklist (view source) (protected)
Module:Category handler/config (view source) (protected)
Module:Category handler/data (view source) (protected)
Module:Category handler/shared (view source) (protected)
Module:Check for unknown parameters (view source) (protected)
Module:Citation/CS1 (view source) (protected)
Module:Citation/CS1/COinS (view source) (protected)
Module:Citation/CS1/Configuration (view source) (protected)
Module:Citation/CS1/Date validation (view source) (protected)
Module:Citation/CS1/Identifiers (view source) (protected)
Module:Citation/CS1/Utilities (view source) (protected)
Module:Citation/CS1/Whitelist (view source) (protected)
Module:Citation/CS1/styles.css (view source) (protected)
Module:Disambiguation/templates (view source) (protected)
Module:Find sources (view source) (template editor protected)
Module:Find sources/config (view source) (template editor protected)
Module:Find sources/links (view source) (template editor protected)
Module:Find sources/templates/Find sources mainspace (view source) (template editor protected)
Module:Message box (view source) (protected)
Module:Message box/ambox.css (view source) (protected)
Module:Message box/configuration (view source) (protected)
Module:Namespace detect/config (view source) (protected)
Module:Namespace detect/data (view source) (protected)
Module:Pagetype (view source) (protected)
Module:Pagetype/config (view source) (protected)
Module:Pagetype/disambiguation (view source) (protected)
Module:Pagetype/setindex (view source) (protected)
Module:Pagetype/softredirect (view source) (protected)
Module:SDcat (view source) (protected)
Module:String (view source) (protected)
Module:Unsubst (view source) (protected)
Module:Wikitext Parsing (view source) (protected)
Module:Yesno (view source) (protected)

Return to Telecentric lens.

Retrieved from "https://en.wikipedia.org/wiki/Telecentric_lens"