What is the difference between the effective focal length and the back focal length?

我们十分重视您的隐私

Edmund Optics 使用 cookies 来优化和增强我们网站的功能和内容。点击"确定 "以获得完整的用户体验，点击 "详细信息 "按钮可查看有关我们使用的 cookie 的其他信息。我们不会出售从营销 cookie 中获得的有关您的信息，我们仅将其用于改善您在Edmund Optics 的体验。

自定义

详情

必要的cookie能够通过启用诸如网页导航和访问网站的安全领域等基本功能以使网站可用。若没有这些cookie，网站将无法恰当运行。
- Cookiebot
  1
  了解有关此提供商的更多信息
  CookieConsentStores the user's cookie consent state for the current domain
  最大存储时长: 1 年类别: HTTP Cookie
- Google
  3
  了解有关此提供商的更多信息
  该提供商收集的部分数据用于个性化和衡量广告效果。
  test_cookieUsed to check if the user's browser supports cookies.
  最大存储时长: 1 天类别: HTTP Cookie
  rc::aThis cookie is used to distinguish between humans and bots. This is beneficial for the website, in order to make valid reports on the use of their website.
  最大存储时长: 永久类别: HTML 本地存储
  rc::cThis cookie is used to distinguish between humans and bots.
  最大存储时长: 临时类别: HTML 本地存储
- edmundoptics.com.tw
  1
  QuoteID待定
  最大存储时长: 14 天类别: HTTP Cookie
- edmundoptics.com
  eogo.edmundoptics.com
  radar.cloudflare.com
  3
  __cf_bm [x3]This cookie is used to distinguish between humans and bots. This is beneficial for the website, in order to make valid reports on the use of their website.
  最大存储时长: 1 天类别: HTTP Cookie
- eogo.edmundoptics.com
  1
  BIGipServer#Used to distribute traffic to the website on several servers in order to optimise response times.
  最大存储时长: 临时类别: HTTP Cookie
- sealserver.trustwave.com
  www.edmundoptics.com.tw
  4
  AWSALB [x2]Registers which server-cluster is serving the visitor. This is used in context with load balancing, in order to optimize user experience.
  最大存储时长: 7 天类别: HTTP Cookie
  AWSALBCORS [x2]Registers which server-cluster is serving the visitor. This is used in context with load balancing, in order to optimize user experience.
  最大存储时长: 7 天类别: HTTP Cookie
- service.mtcaptcha.com
  1
  mtv1ConfSumThis cookie is used to distinguish between humans and bots.
  最大存储时长: 临时类别: HTTP Cookie
- www.edmundoptics.com.tw
  3
  .AspNetCore.Antiforgery.#Helps prevent Cross-Site Request Forgery (CSRF) attacks.
  最大存储时长: 临时类别: HTTP Cookie
  .AspNetCore.Mvc.CookieTempDataProviderPreserves the visitor's session state across page requests.
  最大存储时长: 临时类别: HTTP Cookie
  UMB_SESSIONStores domain prefix to determine whether it holds https or http URL properties.
  最大存储时长: 临时类别: HTTP Cookie
偏好cookie能够使网站记住更改网站行为或外观的信息，就好比您的首选语言或所在地区一样。
- LiveChat
  3
  了解有关此提供商的更多信息
  __lc_cidNecessary for the functionality of the website's chat-box function.
  最大存储时长: 400 天类别: HTTP Cookie
  __lc_cstNecessary for the functionality of the website's chat-box function.
  最大存储时长: 400 天类别: HTTP Cookie
  __oauth_redirect_detectorAllows the website to recoqnise the visitor, in order to optimize the chat-box functionality.
  最大存储时长: 1 天类别: HTTP Cookie
- edmundoptics.com.tw
  1
  chatEngaged待定
  最大存储时长: 14 天类别: HTTP Cookie
统计cookie能够通过收集和匿名报告信息帮助网站拥有者了解访客与网站互动的方式。
- Convert Insight
  3
  了解有关此提供商的更多信息
  _conv_rThis cookie is used as a referral-cookie that stores the visitor’s profile – the cookie is overwritten when the visitor re-enters the website and new information on the visitor is collected and stored.
  最大存储时长: 临时类别: HTTP Cookie
  _conv_sThis cookie contains an ID string on the current session. This contains non-personal information on what subpages the visitor enters – this information is used to optimize the visitor's experience.
  最大存储时长: 1 天类别: HTTP Cookie
  _conv_vThis cookie is used to identify the frequency of visits and how long the visitor is on the website. The cookie is also used to determine how many and which subpages the visitor visits on a website – this information can be used by the website to optimize the domain and its subpages.
  最大存储时长: 6 月类别: HTTP Cookie
- Livechat
  1
  了解有关此提供商的更多信息
  _livechat_has_visitedIdentifies the visitor across devices and visits, in order to optimize the chat-box function on the website.
  最大存储时长: 永久类别: HTML 本地存储
- edmundoptics.com.tw
  2
  ce_diff_time待定
  最大存储时长: 14 天类别: HTTP Cookie
  ce_ip_address待定
  最大存储时长: 14 天类别: HTTP Cookie
营销cookie用于对网站上的访客进行追踪。其目的是为了显示对个人用户来说相关及有吸引力的广告，因此，对于发布人和第三方广告商来说更为宝贵。
- Convert Insight
  2
  了解有关此提供商的更多信息
  conv_randThis cookie is used by the website’s operator in context with multi-variate testing. This is a tool used to combine or change content on the website. This allows the website to find the best variation/edition of the site.
  最大存储时长: 永久类别: HTML 本地存储
  _conv_sptestThis cookie is used by the website’s operator in context with multi-variate testing. This is a tool used to combine or change content on the website. This allows the website to find the best variation/edition of the site.
  最大存储时长: 临时类别: HTTP Cookie
- Google
  9
  了解有关此提供商的更多信息
  该提供商收集的部分数据用于个性化和衡量广告效果。
  _ga [x2]Used to send data to Google Analytics about the visitor's device and behavior. Tracks the visitor across devices and marketing channels.
  最大存储时长: 25 月类别: HTTP Cookie
  _ga_# [x2]Used to send data to Google Analytics about the visitor's device and behavior. Tracks the visitor across devices and marketing channels.
  最大存储时长: 25 月类别: HTTP Cookie
  _gcl_au [x2]Used by Google AdSense for experimenting with advertisement efficiency across websites using their services.
  最大存储时长: 3 月类别: HTTP Cookie
  IDE待定
  最大存储时长: 400 天类别: HTTP Cookie
  NIDRegisters a unique ID that identifies a returning user's device. The ID is used for targeted ads.
  最大存储时长: 6 月类别: HTTP Cookie
  pagead/1p-user-list/#Tracks if the user has shown interest in specific products or events across multiple websites and detects how the user navigates between sites. This is used for measurement of advertisement efforts and facilitates payment of referral-fees between websites.
  最大存储时长: 临时类别: 像素追踪器
- YouTube
  19
  了解有关此提供商的更多信息
  #-#Used to track user’s interaction with embedded content.
  最大存储时长: 临时类别: HTML 本地存储
  __Secure-ROLLOUT_TOKEN待定
  最大存储时长: 180 天类别: HTTP Cookie
  iU5q-!O9@$Registers a unique ID to keep statistics of what videos from YouTube the user has seen.
  最大存储时长: 临时类别: HTML 本地存储
  LAST_RESULT_ENTRY_KEYUsed to track user’s interaction with embedded content.
  最大存储时长: 临时类别: HTTP Cookie
  LogsDatabaseV2:V#||LogsRequestsStoreUsed to track user’s interaction with embedded content.
  最大存储时长: 永久类别: IndexedDB
  remote_sidNecessary for the implementation and functionality of YouTube video-content on the website.
  最大存储时长: 临时类别: HTTP Cookie
  ServiceWorkerLogsDatabase#SWHealthLogNecessary for the implementation and functionality of YouTube video-content on the website.
  最大存储时长: 永久类别: IndexedDB
  TESTCOOKIESENABLEDUsed to track user’s interaction with embedded content.
  最大存储时长: 1 天类别: HTTP Cookie
  VISITOR_INFO1_LIVETries to estimate the users' bandwidth on pages with integrated YouTube videos.
  最大存储时长: 180 天类别: HTTP Cookie
  YSCRegisters a unique ID to keep statistics of what videos from YouTube the user has seen.
  最大存储时长: 临时类别: HTTP Cookie
  ytidb::LAST_RESULT_ENTRY_KEYUsed to track user’s interaction with embedded content.
  最大存储时长: 永久类别: HTML 本地存储
  YtIdbMeta#databasesUsed to track user’s interaction with embedded content.
  最大存储时长: 永久类别: IndexedDB
  yt-remote-cast-availableStores the user's video player preferences using embedded YouTube video
  最大存储时长: 临时类别: HTML 本地存储
  yt-remote-cast-installedStores the user's video player preferences using embedded YouTube video
  最大存储时长: 临时类别: HTML 本地存储
  yt-remote-connected-devicesStores the user's video player preferences using embedded YouTube video
  最大存储时长: 永久类别: HTML 本地存储
  yt-remote-device-idStores the user's video player preferences using embedded YouTube video
  最大存储时长: 永久类别: HTML 本地存储
  yt-remote-fast-check-periodStores the user's video player preferences using embedded YouTube video
  最大存储时长: 临时类别: HTML 本地存储
  yt-remote-session-appStores the user's video player preferences using embedded YouTube video
  最大存储时长: 临时类别: HTML 本地存储
  yt-remote-session-nameStores the user's video player preferences using embedded YouTube video
  最大存储时长: 临时类别: HTML 本地存储
- edmundoptics.com.tw
  7
  _gaexp待定
  最大存储时长: 14 天类别: HTTP Cookie
  _mkto_trk待定
  最大存储时长: 14 天类别: HTTP Cookie
  gwcc待定
  最大存储时长: 14 天类别: HTTP Cookie
  m待定
  最大存储时长: 14 天类别: HTTP Cookie
  NWB待定
  最大存储时长: 14 天类别: HTTP Cookie
  NWB_LEGACY待定
  最大存储时长: 14 天类别: HTTP Cookie
  wcs_bt待定
  最大存储时长: 14 天类别: HTTP Cookie
未分类cookie指的是我们正在同个人Cookie提供者一起分类的cookie。
- Google
  1
  了解有关此提供商的更多信息
  该提供商收集的部分数据用于个性化和衡量广告效果。
  _gcl_ls待定
  最大存储时长: 永久类别: HTML 本地存储
- Livechat
  2
  了解有关此提供商的更多信息
  @@lc_auth_token:3b0f44ba-5eb5-4bb1-a9e1-2214776a186b待定
  最大存储时长: 永久类别: HTML 本地存储
  3b0f44ba-5eb5-4bb1-a9e1-2214776a186b:state待定
  最大存储时长: 永久类别: HTML 本地存储
- service.mtcaptcha.com
  2
  jsV待定
  最大存储时长: 临时类别: HTTP Cookie
  mtv1Pulse待定
  最大存储时长: 临时类别: HTTP Cookie

Cookie 声明由Cookiebot最后更新于 4/14/25

[#IABV2_TITLE#]

[#IABV2_BODY_INTRO#]

[#IABV2_BODY_LEGITIMATE_INTEREST_INTRO#]

[#IABV2_BODY_PREFERENCE_INTRO#]

[#IABV2_BODY_PURPOSES_INTRO#]

[#IABV2_BODY_PURPOSES#]

[#IABV2_BODY_FEATURES_INTRO#]

[#IABV2_BODY_FEATURES#]

[#IABV2_BODY_PARTNERS_INTRO#]

[#IABV2_BODY_PARTNERS#]

关于

Cookie是网站为了使用我们的用户体验更加有效而使用的小文本文件。法律规定，倘若cookie对于本网站的运营来说是完全必要的，那么，我们便可以在您的设备上存储cookie。而所有其它类别的cookie则需要获得您的许可。本网站使用各种不同类别的cookie。有些cookie是由显示在我们网站上的第三方服务放置的。

您可随时从我们网站的Cookie声明中更改或撤回您的同意。

了解更多有关我们是谁、如何联系我们以及我们的隐私政策如何处理个人数据的信息。您就同意书与我们联系时请说明您的同意书ID和日期

不要出售或分享我的个人信息

What is the difference between the effective focal length and the back focal length?

The effective focal length of a lens is the distance from the primary plane of the lens to the focal point, when focusing light that is coming from infinity. The primary plane is determined mathematically and is located at a point within the lens, therefore making it extremely difficult to work with its position for mounting purposes. The back focal length is the distance from the back of the lens to the focal point of the lens when focusing light from infinity. The back focal length is much easier to use when determining a mounting position for a lens. See the accompanying diagram below:

optical lens diagram

這項內容對您是否實用？

感謝您對此項內容評分！