Back to Basics Photography: What is a STOP OF LIGHT?

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Back to Basics Photography: What is a STOP OF LIGHT?

In the upcoming months John J. Pacetti, CPP, AFP, will be writing a series of basic photography lessons.  To find them all just search “Back to Basics” on our blog. This is the seventh article in this series. John is a frequent visitor to the MCP Facebook Community Group. Make sure to join – it’s free and has so much great information.

What is “a stop of light” and why should I know this?

We’ve looked at ISO, F-Stop and last Shutter Speed. We looked at how each one has an effect on in the exposure triangle.  There is one more item I would like to touch on.

I’m sure you’ve heard the phrase “a stop of light.”  A stop of light is the difference in the amount of light that reaches the sensor between F-Stops.

One F-Stop:

If you move from F4 to F5.6 you decreased the amount of light reaching the sensor by 1 F-Stop.  Remember, the higher the F number the smaller the aperture opening.  Each time you move up one F-Stop you are cutting the amount of light reaching the sensor in half.  The reverse is true.  Remember, the lower the F number the larger the aperture opening.  Each time you move down one F-Stop you are increasing the amount of light reaching the sensor, doubling the light.

A Stop with ISO:

Your ISO works in a similar fashion.  Each move up or down in ISO setting is either an increase or decrease in light equaling one stop of light.  For example: 100 to 200 is one stop of light.  200 to 400 is one stop of light.  400 to 800, one stop, 800 to 1600, one stop.  So, if you move from ISO 100 to ISO 400, you increased you exposure by two stops.  (100 to 200 then 200 to 400).

A Stop with Shutter Speed:

Your Shutter Speed works in the same fashion also.  Each change in Shutter Speed is equal to a stop of light.  For example:  1/30 to 1/60 is one stop.  1/15 to 1/30 is one stop.  1/30 to 1/60 is one stop.  1/60 to 1/125 is one stop.  1/125 to 1/250 one stop, 1/250 to 1/500 one stop.   If you increase your Shutter Speed you’re cutting duration light reaches the sensor by one stop.  If you decrease the SS you are increasing the duration light reaches the sensor camera by one stop.

 

There are mathematic involved in all of this.  You really don’t need to know that, just know that each movement in any of the three parts of the exposure triangle is one stop of light, either increase or decrease.

Each change in any one of the three is compensated by a change in at least one of the other two.  Remember, count the stop changes.

  • *One stop change in ISO requires a one stop change in either SS or FStop to maintain the same exposure.
  • *One stop change in SS requires a one stop change in either ISO or FStop to maintain the same exposure.
  • *One stop change in F-Stop requires a one stop change in either SS or ISO to maintain the same exposure.

Here is an example:

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Confused yet?  I hope not.  Our next article will tie this all up for you.

 

John J. Pacetti, CPP, AFP   -   South Street Studios     www.southstreetstudios.com

2013 Instructor at MARS School- Photography 101, The Basics of Photography  www.marschool.com

If you have question, feel free to contact me at jjpacetti@live.com.  This email goes to my phone so am able to answer quickly.  I’ll be glad to help in any way I can.

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1 Comments and 0 Replies



  1. 1
    Jesse Rinka says:

    I think some may just need to be careful with the way their cameras are setup as far as step values are concerned. I can setup ISO to adjust in 1/3, 1/2 or 1 stop increments. The same goes for Shutter Speed.



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