Have you ever wondered if you meter is giving you the right exposure? Do you ever wonder how to figure out the proper exposure yourself? Well it is possible—with the f/16 rule.

The theory is simple. The basic exposure for a camera on a bright sunny day will be f/16 when the shutter speed matches the ISO. That is it … seriously!

If you have a great sunny day, set your ISO to 200 then set your shutter speed to 1/200 sec. The f/stop should be f/16. If you change the ISO then change the shutter speed accordingly. If weather conditions change, then you change the f/stop.

f/22- reflective sand or snow

f/16- bright sunny day

f/11- bright cloudy day

f/8- slightly overcast

f/5.6- heavy overcast or open shade

Now, this is to get a base exposure to work from. After you have your basic exposure you can make adjustments to fit the photograph you are creating.

In situations where you find that you are shooting with the sun on the back of your subject and their face in the shade (and assuming you are shooting a face on portrait), just make an adjustment by opening up two f/stops. So if the base exposure in the f/16 rule tells you that you should be shooting f/11, then open up two f/stops to f/5.6.

Even if you have a great light meter, there is some comfort in having the skills to know that your meter is in the right ball park. When you can work it out in your head, the chances between success and failure of a photograph is significantly reduced.

In a previous blog post, we talked about exposure and how f/stop affected exposure by adjusting the amount of light enters the camera. The f/stop adjusts the opening (the aperture) with a diaphragm (groups of leafs that adjust to make a larger or smaller aperture). However, that is not all that an f/stop does. There are three functions of an f/stop and we will discuss them here.

1)f/stops are half of the control of exposure (the shutter speed is the other half).

2)f/stops allow the photographer to adjust the aperture for the best definition of the lens.

3)f/stops control depth of field.

As we mentioned before, exposure is determined by the quantity of light (intensity) and the length of time light is allowed into the camera. The shutter speed adjusts the time and the f/stop adjusts the quantity.

f/stops are half of the control of exposure (the shutter speed is the other half).

We have also discussed that when light passes through a different medium it changes speed. This means that when light passes through glass it moves slower than when it moves through the atmosphere. If the glass is crafted properly, the light bends in a very predictable way and you can recreate the light to form a focused image on the film plane.

When the light does not directly focus on the film plane that part of the image is represented as fuzzy spots. These fuzzy circles will translate to the image as out of focus. If the lens is focused on a particular point of a scene, there will be an area in front of and behind that focus point which will represent itself as “in focus” and everything closer and farther away will be “out of focus.” The distance of area that is in focus is called “depth of field” or DOF.

What does this have to do with the f/stop? Well, the f/stop determines the angle light that comes into the lens. With a small aperture there is less competition for light to get into the lens, and that will increase the depth of field. The larger the aperture the more light can come into the lens and the shallower the depth of field.

Now remember that the larger the aperture, the smaller the f/stop number. So f/4 will be a larger aperture than f/8. That also means that if you are focused on a single object at f/8 and open up the aperture to f/4 you will cut your depth of field and less of the image will be in focus.

f/stops allow the photographer to adjust the aperture for the best definition of the lens.

Before I go into detail on depth of field, I want to address what I mean by best definition of a lens. While lenses may have an indicated range of f/2.8 to f/32, that doesn’t mean that the lens will perform at its best at all of those f/stops. Some lenses lose their quality when you go to their extremes. While it is not true of all lenses, a good rule of thumb is to close a lens down or open it up at least one stop to start getting the best performance from a lens.

There are some newer lenses that perform amazingly well opened wide open, but you will have to research which lenses these are. Some lenses are designed only to work at optimum performance wide open.

f/stops control depth of field.

Depth of field is defined as the distancefrom the nearest point of acceptably sharp focus to thefarthest point of acceptably sharp focus of a scene beingphotographed. The depth of field isn’t the same at all f/stops and it also changes as the focal length of the lens changes. When you shoot at f/4 on a 50mm lens and a 180mm lens, the depth of field will be different.

Depth of field also changes with distance. The farther the subject is from the camera, the larger the depth of field. There is a focus point (called the hyperfocal distance) when everything behind the focus point will be in focus for infinity.

The depth of field can be measured with a DOF calculator. CLICK HERE

Adjusting the depth of field is an important to photography. It gives you control over your environment and isolate or integrate your subject with its environment.

Using a large depth of field with 14mm wide angle to integrate the environment.

Using a shallow depth of field with an 85mm lens to separate the subject from the environment.

Understanding photography requires an understanding of art and science. The word photography comes from the Greek “to paint with light.” So in order to create art with photography means you have to understand how light works.

Light is a form of radiation that has been studied by scientists for hundreds of years. Two theories have been around for hundreds of years: quantum theory and wave theory. Quantum theory states that light moves in a single direction. Wave theory also believes that light has wave lengths like sounds. These wave lengths move in vary small oscillations (measured in nanometers). The visible light rang moves from 400-700nm.

Eventually, the two theories were reconciled into a unique quantum wave theory. This makes light unique in many ways.

Another characteristic of light is that, in a vacuum, light travels about 186,000 miles per second. I say “in a vacuum” because when light travels through different mediums, it changes speed. The best example I have is to imagine what it is like to walk through an empty room and then how much more difficult it is to walk through water.

When light moves through a camera lens, the speed of the light changes, and if the glass is given specific shapes it will bend as it moves through the glass. When the light re-enters normal air, it resumes it previous speed and continues on its way.

This is how a lens is able to bend the light (refraction) to capture the light on the focal plane (the flat area that captures the image on the film or computer chip).

The color of light is determined partially by the bandwidth frequency. The longer the wave length the warmer the color: Red sits closer to the 700nm wave lengths. Blues and violets are on the other end of the spectrum in the 400nm area. The color spectrum breaks out exactly like the colors of the rainbow (remember R.O.Y. G. B.I.V.?).Light spectrum chart courtesy of \

Light itself does not have a color. The band width frequency must first react with a material and then bounce back to the eye. Even the blue in the sky is a reaction of the moisture in the air that our eyes register.

The blue color has a tighter wave pattern and reaches our eyes with more energy than the slower frequencies of red. However, as the sun lowers to the horizon, the distance between the sun and our eyes has more atmospheres to work through. By the time the light hits our eyes only the lower frequencies meets our eyes and that is why we see a warm red, orange and pink sunsets.


When light hits a surface, the material will absorb certain frequencies and reflect others. So when you see a green cloth, you are really only seeing the light that is reflected. The red and blue light is absorbed by the cloth.

Light is effected by a medium in three ways: reflection, absorption and transmission.

Now that we understand that light is a linear wave length. It is time to start understanding how to a photography practically deals with light.

Color Balance—Each light source is transmitted at a different light frequency. That means that not all light is white. The sun at noon is about as white as you can get naturally. The sun at sunset is red. The light is different in incandescent light bulbs and fluorescent lights.

Photographers need to know how to measure the light in order to know how to deal with it. The most convenient way to describe color is by degrees Kelvin. Degrees Kelvin is a measurement of whiteness (i.e. the amount of pure light).

Kelvin is a measurement of heat. Zero degrees Kelvin is equal to -273 Celsius. If you are wondering why that number, well that is because at -273 Celsius is absolute zero. Nothing can get colder than zero degrees Kelvin. That also means that all light is absorbed and anything that is zero degrees Kelvin is absolute black.

If you have every seen a piece of metal heat up, you will notice that it changes color. The hotter it gets the more it starts to glow. At first it will glow red. Eventually it will glow blue and then white. That color can be measured in degrees Kelvin.

Daylight, or pure light, is approximately 5000-5500 degrees Kelvin. An incandescent bulb burns approximately 2000 degree Kelvin. Fluorescent lights can be 3500, 4500 and 6500 degrees Kelvin.

If your camera has precise color balance control, it will probably allow you to adjust both the default settings (incandescent bulb, fluorescents, daylight, cloudy day, and flash) AND your camera will also have the ability to adjust the specific Kelvin temperature.

Color Relationships—Color and Light can also be defined by its three qualities: hue, brightness and saturation.

Hue is the actual color (or wave length) reflected by an object. The primary colors are red, green, and blue (remember the rainbow?). There are also complimentary colors, which are even mixes of each of the primary colors. These colors are cyan, magenta, and yellow. Many photographers represent these colors in a wheel. This makes it easier to see the association of colors.

phtoographic color wheel

Brightness is the color of the light independent of its hue. This means you can have a bright blue and a dull blue. Think of adjusting the brightness on your monitor. Even though you can make the screen brighter and darker, the hue remains the same.

Saturation is the degree of black and white that is added to a hue. Think of it like mixing a color with paint (white and black).

Understanding these fundamentals are important to a photographer. It will allow you to learn how to adjust the color balance of your film or digital camera. Understanding how light works will also help you later on when you are crafting light for specific effects.