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Do You Know How F Stops, Shutter Speeds, And Iso Are Related? |
By:
Bob Kahn |
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Do You Know How F Stops, Shutter Speeds, And Iso Are Related?
Bob Kahn
Do you know the secret formula of F Stops, Shutter Speeds and ISO?
When you think that the relationship between your F Stop and Shutter Speed, Focal length of your lens, and your ISO can make such a difference in the final image you create, it is surprising how few photographers actually understand the intricate relationships between them.
We will explain each part individually, then discuss how they interact.
F-stops
Although you might have heard rumors to the contrary, the origin of the term F Stop is based on the initial of the inventor.
How much light comes through the lens is determined by the F stop setting, which refers to the degree of opening of the lens diaphragm.
Shutter Speed
Film cameras utilized a variety of types of shutters that controlled the amount of light that hit the film by controlling the length of time the light was allowed in. Today the same principle applies, but with digital cameras the light hits the "Digital Image Capture" component in the camera.
ISO
With both film and digital cameras, a standard was needed to specify how much or how little light is necessary to create an image on the film or the Digital Image Capture device. With film, the term was ASA, and recently the standard used is ISO.
With films of different speeds, we used to have to set the "film speed" on our camera. In the new digital cameras, we still set a "film speed", but in this case it makes a change in the electronic setting of the digital capture device (CCD or other type of chip).
What does matter is that we can use the ISO to control our cameras to achieve a desired result we will discuss further in this article.
FOCAL LENGTH OF LENSES
What we will do in this article is show you how all of these elements come together to achieve desired effects depending on requirements of the assignment.
Example 1
We are outside- bright and sunny.
We want to use a long, telephoto lens to capture a subject far away.
We will hand hold the camera. No tripod.
Even though our camera lens has a stabilizer feature, it's not 100% effective, so we will need a fast shutter speed to prevent "shake".
Setting ISO to 400 will usually allow Shutter Speed of 500-1000 with F Stop at F11 to F15.
Next, we'll take up an example that may be more of a challenge.
Example 2
We are outside, cloudy, not very bright.
Our subject is still at a distance, and we want to use a long, telephoto lens to capture the shot.
No tripod. Hand held camera.
Since we can't depend on the stabilizer lens 100%, we need a fast shutter speed to prevent the camera shake effect in our image.
So now it's time to make choices-
a. if you want to maintain your shutter speed, you could increase the ISO.
b. you can reduce your F Stop (open your lens) You sacrifice the amount of area in focus (Depth of Field)
It's starting to get a bit complicated, so we'll explain how these elements relate to each other.
When you increase/decrease your F Stop one full stop- 5.6 to 8, or 2.8 to 4, reversed, these are full F Stops.
When you increase/decrease Shutter Speed, from 125th to 250th of a second, or 1000th to 2000th of a second, or reversed, are double, or if reversed, allow double the amount of light, or the amount of light that will effect your "film".
Equation: If you increase your F Stop from F8 to F11 you "Lose" one full stop of light.
Increasing shutter speed from 1/500 to 1/1000th of a second results in "losing" one full stop of light.
Doubling ISO from 400 to 800, or 800 to 1600, gains one full Stop of light.
Notice that when working with ISO, F Stops, or Shutter Speeds, we refer to the changes in values at "Stops of Light".
Relationships
Each of these elements can be used to control the camera settings. Control Depth of Field (amount of area in focus). Control movement, stop movement, allow movement to create effects. Use ISO for controlling amount of light.
In Practice
If you have your lens set at F8 and 250th of a second Shutter Speed and you need to open your lens to reduce your Depth of Filed, for the purpose of making your backgrounds out of focus, open your lens to F4, and increase your Shutter Speed to 1000.
In this example you opened your lens 2 stops, as well as increasing your Shutter Speed to 1000. From 250 to 500 doubled the Shutter Speed, then from 500 to 1000 doubled the Shutter Speed again.
If in the above scenario you were using an ISO of 800, you could reduce the ISO to 400, thus reducing the light by which would allow you to only increase your shutter speed once (double), from 250 to 500.
If you are taking pictures with your camera set on "Program" you are missing out on what the real creativity you are capable of with your "fully adjustable camera".
Learn what these settings can do for you and your "creative world" will explode.
At various times I have been thought of as a critic of "Photojournalistic Style" photographers. Believe me, I have nothing against them or any other "Professional" photographers who have not taken the time to learn the simple technical information I present here.
So many eager individuals, with a love of photography and some small successes, decide to jump into the business of Professional Photographer, before they know the basics of what it takes to create the beautiful pictures that become treasured records of their clients' life events.
Simply being told by friend and relatives that they "have a good eye", is simply not enough. There is not question, they achieve images, but are they achieving the best image they can achieve? When we get our haircut, or our visit our Dentist to remedy a painful toothache, we expect these people to do the best they are capable of, not just what they can get away with.
In our next chapter we will discuss how this all works with electronic flash.
You have the new camera, now what? Bob Kahn, Master Photographer, offers free lessons starting with basic technical elements, plus skills of posing, lighting, and composition, and how to put it all together to http://www.prophotohelpdesk.com/ become a successful professional photographer.
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Article Source: http://www.statssheet.com/articles/article70867.html |
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