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What Are “Stops” in A DSLR?
Probably one of the most misunderstood terms in beginner photography is “stop.” Imagine hearing, “I need three stops of brightness. Stop up the ISO 200 to 400, stop down the speed from 1/60 to 1/30, and stop up from (f-stop) 5.6 to 4.” It’s statements like this, and the mathematical explanation, that cause most people to leave their camera on Automatic mode and never venture into manual modes. The reality is that the math and “how it works” doesn’t really matter.
A 9 year-old can understand how to use a microwave, but 1 in 5,000 people (if that) understand, truly, how a microwave works. Many professional photographers have no idea about the inverse square law and how it functions to calculate aperture size. However, every single one of them understands how stops are used. On the other hand, there are quite a few nerds who can rattle off the math, but cannot control a camera whatsoever. The purpose of this article is NOT to explain how stops work, but instead explain how they are used to become a better photographer.
One of the main reasons that the term stop is so confusing is that has multiple meanings (only two of which are important for this article). This is going to be a bold statement and I’m probably going to get hate mail for saying this, but the only important thing that really matters about the word stop (as far as taking better pictures goes) is that it indicates that something is doubled or cut in half. At our photo studio in Nashville and Louisville, we have all kinds of books and charts which talk about stops, but at the end of the day, a stop really is just that simple.
Memorize this: A stop means doubled or halved. 1 stop up, means doubled. 1 stop down means cut in half. 2 stops of light up means four times the amount of light (double then double again) and 3 stops of light down means 1/8th the light (cut in half, then half again, then half for a third time).
As an example, imagine you are out in the sun and you need a pair of sunglasses that block exactly half of the sun hitting your eyes. You could say, “Hey. I need a pair of sunglasses that block 1 stop of light.” After you put them on, the sun is still too bright, so then you say, “Actually, I need a pair that only allow a quarter of the light in.” In other words, two stops down of light. The first stop cuts the light in half, and the second stop cuts that half into another half, which results in a quarter of the original. 1/8 is 3 stops down, 1/16 is 4 stops down, and 1/128 is 7 stops down.
In photography, this is exactly how we speak when talking about adjusting light. If we need to double the amount of light let into the camera, we “stop up” the light by one stop. If we need to cut the light in half, we “stop down” the light by one stop. If we want to allow in 16 times the amount of light that is already coming in, we need 4 stops of light (the first doubles it to 2x, then doubles it again to 4x, then 8x, then 16x). Remember, each stop either doubles or cuts the previous in half.
The main reason photographers use this terminology is to have a common language to measure light adjustments that everyone can agree on. (Again, I’m simplifying here, and will get more hate mail, but I’m not a purist and this is the easiest way to understand this).
How to actually apply a “stop”
There are three main controls on a camera: ISO (sensitivity), Speed, and Aperture. EACH ONE has different sets of numbers, but the one thing they have in common is that increasing or decreasing each one of these controls has the effect of doubling or cutting the final light in half. Tattoo this statement on your forehead and internalize it; this one concept will completely revolutionize your ability to understand how to control the light in your picture (let’s face it, without light, all of your pictures would be pitch black, and people would make fun of you).
The ISO is how sensitive the film or sensor on your camera is. It’s commonly measured in 100, 200, 400, 800, etc… Forget the technical of why these numbers exist, and just remember that going from 200 to 400 means 1 stop of light UP, and going from, say 1600 to 200 means 3 stops of light down (cutting your number in half 3 times from 1600 to 800 to 400 to 200).
The shutter speed is how fast the aperture opens and closes. So, 1/30 of a second is twice as long as 1/60th of a second. Because the aperture is open twice as long, it lets in twice as much light. Therefore, 1/30 is one stop up from 1/60. 1/240 is 4 stops down from 1/15. (Again we go from 1/15 to 1/30, then to 1/60 to 1).
The aperture is the opening in the camera which allows light in and it’s measured in what’s called f-stops and the numbers are displayed in a series like 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22. Again, forget for a moment why these numbers are in this series and just remember that 11 is two stops up from 22 (here a smaller numbers means a larger opening and more light). 5.6 is 4 stops down from 1.4.
Bringing it all together
Understanding that all three controls are in increments of “stops” is the key of enlightenment. If you take a picture at ISO200, 1/60, and f8 and you need the picture 4 times brighter, you now understand that there are three options: 2 stops up from ISO200 to ISO800, 2 stops up from 1/60 to 1/15, or 2 stops up from f8 to f4. Each of these decisions will have a creative visual effect, but they all will have one thing in common: Allowing four times the light into the final picture.
Callie Colleen Smith
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