Do You Know The Secret Of F Stops, Shutter Speeds, And Iso?

F Stops, Shutter Speeds and ISO- How do they relate?

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

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

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

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.

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)

Now that you know that the ISO setting in your digital camera compares to the film speed setting in a film camera, we will describe the details of the effect that you can achieve with the ISO setting later in this article.

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

Location: outside, bright sun

The subject is far away, and we will use a long telephoto lens to capture the image.

Camera to be hand held, not using a 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".

Using a 400 ISO, we can normally set our Shutter Speed to 500-1000, and our F Stop at F11-F15.

In this next example, you might have problems taking pictures of your subject.

Example 2

Location: outdoors, 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.

Now you have to make choices-

a. increase ISO to allow you to keep your shutter speed the same as in Example 1.

b. If you reduce your F Stop (open your lens), you will sacrifice the total of area in focus (Depth of Field).

Now we will sort out the relationships among these factors.

Increasing or decreasing F Stop one full stop would be 5.6 to 8, or 2.8 to 4, or vice versa.

Increasing Shutter Speed, from 125th to 250th of a second, or 1000th to 2000th of a second allows half the amount of light that gets to your "film", and conversely, reducing Shutter Speed from 250th to 125th of a second, or 2000th to 1000th of a second doubles the amount of light that hits 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.

Important note: "Stops of Light" is the terminology we use whether we are discussing the effects of working with ISO, F Stops, or Shutter Speeds.

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

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.

Here you opened your lens 2 "Stops". The change in your Shutter Speed from 250 to 1000, in effect doubled from 250 to 500, and then doubled again from 500 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.

There are some in the photographic community who believed I was generally criticizing the "Photojournalistic Style" of photographers. However, that has not been my point. The basis of my criticism of the photojournalistic genre was that those who pursue that style, without learning the basic technical elements presented here, are shortchanging themselves and their customers. With the basics down pat, their pictures can be ever more beautiful and intriguing.

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.

Would you go to a Doctor whose credentials consist of letters of testimony from their friends and family that they always wanted to be a Doctor, and they seem to have natural abilities to help people? I think not. As a Professional Photographer you will serve your clients best by preparing and learning so that you provide expert service. Without basic skills, you may be doing the best you can, but is it good enough to be called a Professional?

Next chapter- How all of this works with your electronic flash

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Do you want to be a Professional Photographer? Bob Kahn, Master Photographer, offers free articles starting with basic technical elements, and techniques of posing, lighting, and composition, and how to put it all together to become a successful professional photographer.

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