Focal Lens Length Tutorial

Author: John Honovich, Published on Nov 17, 2014

3mm, 6mm, 2.8 - 9mm, 5 - 50mm, etc.

Camera specifications often list lens lengths but what do they mean?

These metrics are important in determining the correct camera coverage and Field of View (FoV). In this tutorial, we look at:

  • What lens focal length impacts
  • The relationship of imager size
  • Common lens length ranges and their uses
  • Limitations of using focal lens length
  • Manufacturer variances between focal length and AoV
  • Picking the right lens length

***, ***, *.* - ***, * - ****, ***.

****** ************** ***** **** **** ******* *** **** ** **** mean?

***** ******* *** ********* ** *********** *** ******* ****** ******** and ***** ** **** (***). ** **** ********, ** **** at:

  • **** **** ***** ****** *******
  • *** ************ ** ****** ****
  • ****** **** ****** ****** *** ***** ****
  • *********** ** ***** ***** **** ******
  • ************ ********* ******* ***** ****** *** ***
  • ******* *** ***** **** ******

[***************]

Focal **** ****** ** *** / ***

***** **** ****** ** *** ******** ******** ******* *** **** and *** ****** / ******. ** ** ********* ** ************ because ** ** *** ******* ****** ** *** *** ******* / ***** ** **** (***) ** * *****. ***:***** ** **** (***) ********

Lens ****** ******

*** ****** *** ****, *** ******** *** ***** ** **** / **** ********; *** ******* *** ****, *** *****. **** is * ******** ********* ******** **** *** ******** ******* *** lens *** *** ******, ** *** ***** ***** *****:

lens sensor

*** ****** *** **** **, *** ******* ** ** **** from *** ******, ********* ** * ******** ***.

********, ** *** **** ** *****, ** **** ** ***** to *** ****** *** ******** * ***** ****, **** **:

Impact ** ****** ****

****** *** ***** **** ****** ** *** ******* ****** ** FoV ** ************, *** **** ** ****** **** (*.*., ¼”,*/*”,*/*”, etc.) **** ******* ****. ********** **** *****, *** ****** *** imager, * ****** *** / **** *** ** ********. **** is *** * **** ****** ** **** ************ ************ ******* are */*” (** ***** – ** */*.*” ** */*.*”). *******, there *** ** ****** ***********, **** ** *** ***** ****** is *** ****, ** *** ****** **** ** *** ****** is *********. *** ****, ***:************ ****** ****** ********

Rule ** ***** - ***** ****** ** ***

***** *** **** ****** */*” ******, **** ** *** *** / ********** *** ** ******* *** ****** **** ******:

*** ***** ************ ** **** ******** *** **** **********.

Common **** ****** ******

** ********, ************ ******* ********* **** ** *** ** * lens ****** ******:

  • ******* – ***** *** ******** ***** **** ***** ***** *** comes **** **********, **** *** **** '*******'. ***** **** ********* require ********* ******** ** ******* * **** / ********* *****. While ** *** ******* ********* ******, ************** *********** ******. *** our***** ** ********* ********* / *** ******* *******.
  • '******' – *** – ****: *** ***** ****** ** **** cameras **** ** **** ***** (******* ** ** ** ******* FoV).
  • ********* – **** – ****: ***** **** ******* ** ** come **** ****** ** **** *****, **** ** ******** */** ****** *** ** ********* *** ********* ** ******* (typically *** **** ******)
  • ***** ********* - *****+: ****** ** **** ***** *** ********** ones **** ** *** / ******* ******* **** *** **** (typically ***+ **** ***** **** ** ****)

Warning: ************ ***** ****** / *** *********

****** ************* ********* ******* *** / *** ********* ** ******* a ***** ******. *** *******, ************* *** **** *** *********** to **** **** * ****** ** **** ***** ** ********* 50mm ** **** * ****** ** *********.

*******, ****** ************'* ***** ******* ** *** ****** *** ** to *********** / ************ *** *** , ********** **** ******* focal *******. ********* ** ** ******* ** *** **** ** the ****** ** **** ** **** ** ******* *** ************ of *** **** ****** **** *** *********** ************. ********** ** the *****, *** ******** ** ** ****** **** ******* / lenses ***** ** ***, *** ***** ******. **** ***** **** easy ********** ********* ** ****** ******, **** ******** ****, ** *** calculator.

Lens ***********

*** ****** *** **** ******, *** **** ****** ***** *********** will *****:

  • ******** ***** *******: **** ******, ********** ********* **** ****** ** ************, ********** have ******** ***** ******* ******** ** **** ***** ******* / ppf ******* ***** ********. ** *** *** ******** / ***** **** **** ***********, *** *** **** ** ********** **** extra ***** *******. ***:* ***** **** ** **** ****** *** **** *****
  • ******** *** ***** ***********: **** **** ****** (** **** ** **** ***** ****) typically **** ************* **** ***** **** '******' ****** ** *** *** ** 10mm *****. ************, ********** **** ***** *****, *** ****** *** lens *** ****** *** * ****** (****** **** **** *********** *******).
  • ***** ** ***** ******: ************ ******* **** ****** **** ***** ** ***** ****** where ******* ****** *** ** *****. **** ** ******* **** usually *** ********** ***** ****** *** **** ******** **** *** more **** * **** **** **** *** ******. *******, **** long **** **** ***** ******** **** *** ********** **** ** resolve *** ***** **** ******* ** **** ****-**** ******. ****** our***** ** ***** ********.

Picking *** ***** **** ******

*** ******* *** **** ******, *** **** *** ****** *** capture. *************, *** ***** *** ******* ****, *** **** ******** is *** ********** ****** ********. **** ** *** ****** ***** are ******* **** **** **** ** * ********* ******* ******. Since ** ** *********, *** ******* ****** ** ****** *** since *** *** ** ** ****, *** *** ******* **** 'fuzzy' **** ** **** *** ***** ** *** ******.

*** **** **** ** ***** ** ** **** *** *** no ***** **** *** **** ** ******** – *.*., **** what *** **** ** *******. *******, **** *** ** ***** as ****** **** ** ******* * *** ** ****** (*.*., I **** *** **** ** *** ******* *** **** *** license ****** ** *** **** ******** **).

** **** ***** ****, ****** *** **** (***) ** *** metric **** ** **** ********* *** **** *** *** ** without ****** *** ******* ** *** **** ******** ** ***** that **** **** ** *****. ****** **** ****** ******* ********** ****.********** **** *** ****** ************ ********* *** ******* ******** ******* *** *** *** *** your ******** ************.

[****: **** ******** * **** ******* ***** **** ************* ******** upon.]

Comments (22)

**** ** *** ** *** **** ******** ** **** ***** that * **** **** **** (*** * **** **** * lot ** ****).

***** *******. ** **** ** *** ****** **** ****** ***.

***** ****** ** ***** ************* ** *** ******** ********, *** it's **** ** *** ** ********* ****. *** ***** ****** of * ****** **** ******* *** ** ********* ** *** distance ******* *** **** *** *** ***** ***** ******** ***** rays *** ******* ******** ** *** ****. *******, *** * lens ****** (**** **** ********), **** ******** *** *** ****** always ** ********** ** * ******** ***** ******* *** ****** of * ****. *** *******, ********-**** **-***** ****** *** **** the ******** **.*** ******** ******* *** **** ***** *** *** sensor, ********** ** ***** ******.

* ***** ***** ****** *** ** ********** ********* ** *** strongly *** **** ****** ****** ***** ********. * **** ****** with * ******* ***** ****** ****** ***** **** ******** **** strongly **** * ****** **** * ****** ***** ******. **** lens *** ********* ***** ***** **** ** **** ******** ****** together ** ****** * **** ***** ****. * **** **** a ****** ***** ****** **** *** ******** ***** ***** **** together, *** ******** **** ***** **** **** **** ***** ******** angles, ********* * ****** ***** ** ****.

******* *** ********* ***** *******, ** ** ***** ******** ** design *** *** ****** ** **** ***** ****** *** ******* at *** **** ******** **** **** *** ****, ******** **** to ** **** *************** ** *** **** ******.

******, ****** *** *** ***********. **** *******!

****:

***** **** ******is *** ******** ******** between the lens and the sensor / imager.

******:

...***** ****** ** ********not * ******** ******** anywhere in or on the lens.

**** **** ***** ** ****** ** ****** ***** ** ****? Or **** ******** ** *****?

***** *** ** ** **** ******** **********. *** *******, *** 1000mm ****** *** *** ********** ****** **** * *** ****.

****** ********:

**** ******** ******* **** **** *** ****** ***+***** *******. *** i **** **** **** ****** (** ******) **** **** ****.******** ***** ******.

******* ** ***** ***** ** **** ***** ******. ***** **** **** *.***. ***** *******, ****** *** **** attached ** ** ***, ** **** ******** ** ****** ***** to ****.

** **** **** *** *.***, ***** ** ** *** ** actually ******* ** **** ****?

**** ********. *** *.*** ***** ****** ** ******** *** * physical ******** ******** ** ** ** *** ****. ** ** a ******* ** *** "***** ******* *****" ** *** **** system. *.*** ** ********** **** (***** ***** ********), *** ****** give ***** * **-****** ***** ** **** ** * */*" sensor. *** ************'* ************* ***** **** **** ******* ** *** exact ***** ** **** *** **** **** *******.

***. **. *** ******, *** **** ** **** '***!

**, ** *** **** ******** ********, *** ** ** ********* how ***** ***** ***** ** ** *** *** ***** ***** lump ****?

** ******** **** ****** ******* ****** ** ******* ** *******/**** than ************ ***** ******, *** ********* ******?

**** ***** **** **************.

* **** ***** ** **** ******://*****.**.****.***/~****/*****/******/*********.***

************* *** **** ** ******** ** ******* * **** **..

***** ************ ******* *** ***********!

** *****
***'* *** *** **** ** ***?

***'* *** *** **** ** ***?

**** ********. **** *** ********** ******* ******* *** ***** **** to ******** *** **** *****.

** *** ** *** *** ********* ** ********* **** ** are ******* ***** *** ***** ** ****, *.*., *** ***** covered ** *******. **** ** ******* *** *** ********** ******** the ***** ** **** ****, ********* ********* ** **** / meters.

*** *** *** *** ***** ** **** ****************, ****** *********** FOV ****** ** *** ****** ***** ** ***** (*******) ** a ***** ********.

**, *** ***** (*) ******* ** *** (*) *** ******** (*) ** ***** ****:

*= *** ***(*/*)

********* *** ** *** ** **°, **** ***** *************

** ** @ ******** ** **
*** ** @ ******** *** **

****, *** **** **** ******** ****** ** *** **** (********** angle ** ****) *** *** **** (********** ***** ** ****), though ****** *** **** *** **** *** ** *********** ** desired**

***** **** ***** *****

* **** **** ********* ******* *** **** * **** ***** adjustment, ** *** ** *** ********* ******** ****** ******* **** adjustment?

*** *** ******* *** **** ***** ****** ***** ********* ******?

***** **** ** **** * *** *****, ******** * ***** it.

Model *:
****://********.*********.***/**/*****************************.****
*/*.*" *********** **** ****
*.* **, ********** ***** ** ****: ***°
* **, ********** ***** ** ****: **.*°

Model *:http://overseas.hikvision.com/en/Products_accessries_756_i6109.html
*/*.*" *********** **** ****
*.* **, ********** ***** ** ****: **°
* **, ********** ***** ** ****: **.*°

*** **** *** * ******* **********, *** *** ********** *** has ******* **********.
* *** **** ********** ** **** ****** *** ***'* ****** find * **** *********** *** **.

*** *** ******* *** **** ***** ****** ***** ********* ******?

#*, **** ***. **** ******** ******* * *** ****** **** manufacturers.

*** ****** ****** ** **** *** ************ ** ***** * larger ****** ********** **** **** ** ***** ******** *** (*.*., a *** '******' *** ** **** * ****** *.*** ****) which ***** *** ****** ******** *** **** ** **** **** the ***********. ***** ******* ** **** ***** ***** ********* ** what ****** ***** *******, ***.

** **** **** **** **** ***** ** ** **** ******** out ********* ************ ***** **** ***** *** ****** ********* *** *** **** different **** **** ** '*************' ****** **. ** ** *** of *** ****** ** **** ********* ** ******** ****** **** their ********* *** ****** **** *** *********** ***.

*** **** *** * ******* **********, *** *** ********** *** has ******* **********.

****, *** **** ****** *** *** ********** **** ** *** fact **** *** **** ***** (*/*.*" *** */*.*") *** ******************************* *** *** *** (*** *** **) *** ***** ************************.

***** *** **** **** ** **** ***** ** ******** *****, you *** **** ***** *** ***** ** ******* ** *** aspect *****.

** ** **** ************2560x1920 sensor, which are 16:9 and 4:3 ratios respectively.

******** **** ***** ** ** ******** ** *** **********, ** have * **** ******* ****** ** *** ****** ****, ***** translates ** * ******** ****.

* *** **** ********** ** **** ****** *** ***'* ****** find * **** *********** *** **.

***/***, ******** ****** ***** **** ** ** **** ****** ** infer ****, *** *** **** **'* ****** **** ******* **** in **** ********* ******, ** ** *** ******.

***:**** ********: **** ** *** **** ** ** ** * 1/3" ******?

** ** **** ***************************, ***** *** **:* *** *:* ****** ************.

**'* ****** **** ******* **** ** **** ********* ******, ** is *** ******.

****'* * ****** **** *****. ****** *** *******!

** *****,

*** *****: ***** ******/****** ***** ** **** ***** *** : 77 ***.

** *** ***** ********* *****, *** **** ***** ***** *** : ** ***.

** **** **** * **** ** ** * ******* *********?

*******,

*****

***** *****:

**** *****! ***** ****, ***. *** ******* ***** ** ** degrees *** */*" @ ***. *'** ****** *** ***** **** in *** ****** ****.

****** *****... ****** ** ******** *** **** ** ** **** vetting ****** **********.. ********* ****** ** ***... ****** * ***** to *** ** **** **** **** *** '*****-*****'.

**** *******

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