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Do You Know The Secret Of F Stops, Shutter Speeds, And Iso?
Do you know the secret formula of F Stops, Shutter Speeds and ISO?
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.
Before we discuss how the parts fit together, we will first describe each separate factor.
F-stops
No, that name is not derived from a vulgar term. The concept of F stops was invented by a man whose initial was F.
They are the diaphragm, or the opening of the lens. The F Stop determines the amount of light that will pass through the lens.
Shutter speed
With film cameras and digital cameras alike, the shutters may be of different designs, but they all have the same purpose, to control the amount of light hitting the film or the digital image capture device by controlling the amount of time the shutter is open.
ISO
When film was used, a standard was needed to determine how much or how little light is necessary to create an image on the film. Various “speeds” of films were produced which differed in their ability to capture light. The term for that standard was ASA, from American Standards Association. A new term, ISO (International Standards Association), became popular a few years ago.
Even though we don’t use film anymore, we do have the ability to set a “film speed” in our new digital cameras. My understanding of the particulars is that it is actually an electronic change to the DCD (my own term, there are CCD’s and other chips, but for this article their names are not important)
Later in this article we will discuss the use of the ISO to attain a particular result.
Focal length of Lenses
Those are the basics, now for pulling it all together so you can get the results you want based on the particulars of you photo assignment.
Example 1
We are outside- bright and sunny.
The subject is far away, and we will use a long telephoto lens to capture the image.
No tripod, hand hold the camera.
We need a fast shutter speed to keep the camera from shaking. You can’t totally depend on “stabilizer” lenses.
Setting ISO to 400 will usually allow Shutter Speed of 500-1000 with F Stop at F11 to F15.
In this next example, you might have problems taking pictures of your subject.
Example Two
Location: outdoors, not very bright.
Again we want to use a long, telephoto lens to capture the distant subject.
We still will not use a tripod, but hand hold the camera.
We need a fast shutter speed to keep the camera from shaking. You can’t totally depend on “stabilizer” lenses.
So now it’s time to make choices-
a. increase ISO to allow you to keep your shutter speed the same as in Example 1.
b. you can reduce your F Stop (open your lens) You sacrifice the amount of area in focus (Depth of Field)
Let’s explain relationships between all of these elements.
Increasing or decreasing F Stop one full stop would be 5.6 to 8, or 2.8 to 4, or vice versa.
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”.
Formula: Increasing F Stop from F8 to F11 = Losing 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.
To gain one full stop of light, double your ISO, such as from 400 to 800, or 800 to 1600.
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 Real Situations
For example, if your lens is at F8, with 1/250 second shutter speed, and you want to make your backgrounds out of focus, open your lens to F4 to reduce your Depth of Field and increase your shutter speed to 1/1000.
You opened your lens 2 “Stops”. When you increased your Shutter Speed to 1000, you doubled it from 250 to 500, and doubled it again to 1000.
In the above situation, if you had been using an ISO of 800, you would have been able to reduce the ISO to 400, which would reduce the light by 1/2, and then you could increase shutter speed just 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.
Though some “Photojournalistic” style photographers have at times thought I was criticizing their entire body of work, they misunderstand my viewpoint. I want them to realize that by incorporating the basic technical skills in their work, their work will jump to new heights of creativity.
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.
If friends and family tell someone that they take great pictures, that they have a good eye, that’s not enough of a qualification to succeed as a Professional Photographer. Are they creating the best images possible by just using their natural artistic or creative ability? Probably not. If we go to the barber, or the Dentist, or Physician, we expect expert treatment. As Professional Photographers, we should strive for expert achievement, too.
In our next chapter we will discuss how this all works with electronic flash.