F-Stop Tutorial

Author: John Honovich, Published on Oct 13, 2012

To understand low light surveillance, appreciating the importance and role of the f-stop metric is critical. In this tutorial, we explain:

Key Points

  • *** ********* *** ***** ***** **** ****** ******* ********* **** far ***** * *******
  • *** *** ***** ** * *** ******* *** *-**** / low ***** ***********
  • *** ********* *-**** ** ******** ***** ** ***** ** ********* and ******** ** **** **** ** ************
  • *** *-**** *** ** ********* *** ****************

*-**** ******** *** ******** ****** ** ***** **** * **** can ****. ************* *** ******'* ************ *** ** ****** ** the ****** *** * ****** (*, *, *, *, ***.), the **** ****** ** ***** **** ** **** (*.*., * is **** ***** **** *, *.* ** ***** **** *.*, etc.). ****'* * ****** ************ ** **** ******** ** * numbers:

fstop

***********, * **** ********* *** ****** ** *** **** *** the ******** ** *** **** (*.*., */*). ********** **** *****, the ****** *** **** (*** **** ******* ** ***), *** less ***** ****** *** *** ****** *** * ******. *********, smaller **** ******** (**** ** ***** ** ********* *******) ******* the ******* ****, ******** **** ***** ** ****, ********* ** higher * *******. **** ** ***** ******** ****** ********* ************ selection, ********** ** **** *** *********.

What * ******* **** ** **************

**** ****** / ******* ******* * *******, **** ****** ******* the ****** * ****** **** *** **** ******** **** *** iris ** *** *** *** ****. ********** *** ****** ***** **** *******. **** ********, *** * ****** **** ** ******. *******, once *** **** ** ****** *** *** ***, *** ******** limitation ** *** ***** ** *** **** ******. ** ** this ****** * ******, **** *** **** *** *** *** open, **** ** **** ******** **** ********* *** *** ***** capability ** * ****.

Low ***** ***** ***********

***** *** *** ***** *********** ************* *** ****** *-**** *** on ***********. ***** *** ***** *** * **** **** ********** of ***** ******.

** ~* ***, ** *** ******* *** * ******* ******** in ***** **********, **** ************************* * *.* *** ******.

** ***** *.** ***, ********** *** *-**** ******* ********* *** visibility ** *** *******, **** ***** ***** **** * *.* to * *.*. ** **** *****, * *.* *** ******, the ***** ** ********** ****.

*****:

  • ***** ********** * ******* ****** ******* *** ****** ** ***** passed, *** ******* *** ****** ******* **** ******* ** *** overall ***** *********** (*.*., * '****' ******* *** ***** ****** will ****** ******* ******* **** ****** **** * '***' ***).
  • **** *** **** ***** * ****** **** * * **** lens **** ****** ********** ********* * ******* ** ******** ******. This ****** ** **** **** '*******' **** **** ******* *** is ********* **** ******* ****** **** ****** ******* **** ********* do *** **** ******** ******.

Differences ** * *******

*** ********** ******* * ******* *** ** ********* *** **** bigger **** ** *** ******* * ******** **** ************. *** instance:

  • */*.* ***** ** **% **** ***** **** */*.*
  • */*.* ***** ** **** */**** *** ***** ** */*.*

*** ****'**-**** ************ *** *** ********.

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

***** ** ** ********* ** ** ***** ** *-**** *** the ****** ** *** ****:

  • ***** *********** ** * ******* (*.*., */*.* ** */*.*) ********* do *** ****** *** ***** *********** *************, ******** ** **** is ******** *********.********* **** ********** ***** ****** **** ***** ********** ****** ***** * ****** differences.
  • **** ************ ** *** ******* **** *-**** ******* ** *.* or *.*.
  • **** ***************** ******* *-**** *******, **** *** **** ***** *** ***** performance **** ** *** ****. *********** ** ******* ********** **** a ******** ********** **** ************* ***** ******* ******* ******.
  • *******, * **** ******* ** *.* ** ******* ***** ******** poor *** ***** ***********.
  • ************ ***** ***** **** ****** ******* ********* ******** ****, **** ****** **** *********, **** **** **** * numbers *** ********* ***** *** ***** *********** (*/*.* ** *******). For ********, **** **** **** ***** (***) **** * */*.* ***** ***** ********* (***) **** * */*.*, ******* *** ********* **** ** ~*/*** the ****** ** *** **** ***** ****.
  • ******** ****** ** *** *** ******* (*.*., **** ***** *******) typically **** **** * ******* *** **** *** ***** *********** since ******* *** ******** * **** ***** ****** (***** ** or ******) ** * **** * ****** (*/*.* ** ******* is ******). ****** **** ************* ** *** **** ******* ** ** ******** **** *** ******** ***** *** **** but *** ****** ** *** **** ** *********.

Depth ** ***** ******

***** **** * ******* *** *** *** *** *****, **** can ** ******* *** ********** *** ***** ** ******** *** ********* ** ************(*** ******** ** ***** ********). *** ****** *** * ******, ********* *** ******* *** depth ** *****. *** ***** ***** ************ ********* ********:

dof example

***** **** *** ** ******* *** ***********, ** ********* **** not **** * *** ********** ** ************. *****, ** *** destroy *** ******'* *** ***** ***********. *** *******, ******** ** f/1.4 ****** ** ************ *******, */*.* ***** ** ** ***** less *****. ** **** *** **** ** ** *****, ** a **** ***********, *** ****** ***** ********* ******* ******* ****** pure *********. ******, ** **** **** ****** ***** ***** */*.* to ** **** ** **** ********** ** ******* *** ********** to **** *** **** ** ***** ** ******** **** **** (i.e., ** *** **** *** * ******).

*** ************** ** ** *********** ** ***** ************ ****** *** **** ****** *********** ****** and *** ******* ** **** ******** **** ******* *** ******* performance *********** (**** ****** *** ***).

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

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

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