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#STOPSOFLIGHT - Understanding Stops of Light in Photography

If you’ve ever heard the phrase, ‘stops of light,’ and wondered, “what in the world that photographer was talking about?”, Then this article is for you.  Let me teach you what the phrase means as well as understand why it’s important to talk this way in photography.

What are Stops of Light in photography?

 
A stop of light deals with doubling or halving the amount of light in an image in photography.  A one-stop increase means the amount of light doubles.  A one-stop decrease means the amount of light is halved.
Take a look at the images below to see what I mean.

an engagement image of a girl snuggling looking over her grooms shoulder with correct exposure
This image is exposed properly.



an engagement image of a girl snuggling looking over her grooms shoulder over exposed one stop of light
This image is over exposed by one stop.



an engagement image of a girl snuggling looking over her grooms shoulder underexposed one stop of light
This image is underexposed by one stop.

With the above images, you can see how one stop of light can make a vast difference in your image.  Adding a stop of light doubles the amount of light in an image while decreasing a stop of light halves the amount of light in the image.

Why call it stops of light in photography?


This is an oft-asked question and a good one.  The answer lies in the face that you can add or subtract light in three ways in photography:
  1. with the aperture/f-stop
  2. with the shutter speed
  3. by adjusting the ISO
To learn more about any of these components of exposure, click the link.
To darken an image by one stop, you can drop the aperture or increase the shutter speed or lower the ISO.  All three will have the effect of darkening the image by one stop.
To lighten an image by one stop, you could do the opposite, increase the aperture or ISO, or lower the shutter speed.
Let’s say I show you the image below.  You might say, “Kelly, I like the image, but it seems too dark.  Try brightening it dropping your f-stop.”  Doesn’t that just sound weird?  You have no idea why I choose the settings that I did, and why would you arbitrarily tell me to drop my f-stop.  Why not tell me to raise my shutter speed?

This is where stops of light come into play.  It is so much easier to simply say, ‘the image looks one stop too dark.’  How I choose to raise the brightness is left to the photographer, and they may think it’s perfect at that brightness anyway.

Aperture stops and stops of light.

Stops of light also correspond to the f-stop numbers of the aperture.  There are full stops, which means you are doubling or halving the amount of light, as well as 1/2 stops and 1/4 stops.  Take a look at the chart below to see the full stop range of the aperture.

a chart that shows the stops of light for aperture




Dropping your f-stop from f2.0 to f1.4 adds one stop of light, or doubles the amount of light in the image.  Likewise, adjusting your f-stop from f4 to f5.6 removes one stop of light and halves the amount of light in the image.

Shutter speed stops and stops of light.

As with aperture, your shutter speed moves in stops of light.  Below is a chart that shows shutter speeds full stops of light.  Remember, shutter speed is in fractions of a second.


a chart showing the stops of light for shutter speed



Dropping your shutter speed from 1/4 to 1/2 adds one stop of light, or doubles the amount of light in the image.  Likewise, adjusting your shutter speed from 1/15th to 1/30th removes one stop of light and halves the amount of light in the image.

ISO and stops of light.

And finally, just as with aperture and shutter speed, ISO moves in stops of light.  Below is a chart showing the full stops of light with ISO.

chart showing stops of light with ISO



Increasing your ISO from 400 to 800 adds one stop of light, or doubles the amount of light in the image.  Likewise, dropping your ISO from 100 to 50 removes one stop of light and halves the amount of light in the image.

Adding and removing stops of light in photography.


Let’s talk about some real numbers. This can get confusing for some, so don’t feel like you have to memorize this part of the article.  But seeing how all three components of exposure work together to create the correct amount of light in the image can be very beneficial.

Adjusting two settings one stop of light but creating the same exposure.

If the perfect exposure of an image is:
 f5.6 at 1/125th @ 400 ISO
then by increasing the f-stop from f5.6 to f8 (adding one stop of light through the f-stop), and lowering the shutter speed from 1/125th to 1/60th (removing one stop of light through the shutter speed), my exposure (the amount of light) remains the same.
Thus:
f5.6 at 1/125th @ 400 ISO = f8 at 1/60th @ 400 ISO
Both of these exposure readings yield the same amount of light.  The only difference is, the first image has a more shallow depth of field and less chance for motion blur.  The second image has a larger depth of field and more of a chance for motion blur.

Adjusting two settings three stop of light but creating the same exposure.

For the next example, let’s move 3 stops.  The original exposure settings are:
f5.6 at 1/500th @ 1600 ISO
I will add three stops of light to my aperture, changing it from f5.6 to f2.0.  This now gives me a very shallow depth of field.  I added three stops to aperture, so I need to remove three stops from somewhere else to keep the same exposure.  I choose ISO and change it from 1600 ISO 200 ISO, which gives me a much cleaner image with less digital noise.
Thus:
f5.6 at 1/50th @ 1600 ISO = f2.0 at 1/500th @ 200 ISO
We could do this all day.  But this is how you add or remove stops of light to create the same exposure.

 Understanding stops of light in photography is necessary, particularly as you work to create the perfect image.  Reading about it is good, but the real learning will happen as you get out there and take some pictures.  Next time you’re out shooting, try adding one stop of light with one component of exposure while removing with another.  This will help you understand stops of light in photography.

Be safe, be classy, be an artist. 
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