The Basics of Digital Photography: The Exposure Triangle, Part 4

Digital photography is a science as well as an art. With today's fully programmable digital cameras, one can shoot good pictures right from the start even if one had never used a camera of any sort before but good pictures aren't the same thing as great pictures. To make great pictures one has to understand the science as well as the art of photography. "The Basics of Digital Photography," will teach you the science of digital photography.

Chapter one of The Basics of Digital Photography introduced you to the Exposure Triangle. As you may remember, the three corners of our Exposure Triangle are Shutter Speed, Aperture, and ISO. Part 1 of this chapter was devoted to lens aperture and introduced the student to the concepts of f-stop numbers, lens speed, and depth of field. Part 2 of his chapter introduced the student to the concept of shutter speed and how it related too lens aperture when calculating exposure. Part 3 of this chapter introduced the student to the concept of the three systems for rating film speed or the sensitivity of the digital camera sensor to light. The three system being known an ASA, ISO, and DIN systems. In this part, part 4, we will pull it all together and you will learn how to manipulate these three adjustments together to make great pictures when your camera is set to shoot using the "Aperture Priority" mode, the "Shutter Priority" mode, or the "Full Manual" mode.

In "Aperture Priority" Mode, the photographer manually selects the lens aperture computes and sets the shutter speed for proper exposure. In the "Aperture Priority" Mode the photographer can shoot with the ISO set on automatic, in which case the camera will select and set the sensors sensitivity level. In the "A" Mode, the "Aperture Priority" Mode, the photographer can also choose to manually select the ISO that he or she wants to shoot at.

In "S," or the "Shutter Priority" Mode, the photographer chooses the best shutter speed to shoot at while the camera computes and sets the lens aperture based on the lighting conditions and selected ISO setting. If the photographer chooses to dial in an ISO setting manually rather then set the ISO to automatic and let the camera compute and set the ISO, the onboard computer will consider this setting when selecting lens aperture.

In "M," the "Full Manual" Mode, the photographer has full control over the shutter speed, lens aperture, and ISO settings. In order to use the "M" Mode correctly one has to understand metering modes and how to select the proper one to use in different shooting scenarios. We will cover the three most common metering modes found on most digital cameras in the next chapter of "The Basics of Digital Photography."

As a new digital photographer you may choose to leave the ISO set to automatic at first while mastering the "A" and "S" modes of shooting. That is actually a good approach to take. The first thing I tell every new photographer is to make their daily goal to be to master one new feature that their camera has to offer them. I used that approach with my grand daughter who was inspired me to write these tutorials. Every time you take your camera out, make it your goal to learn how to use another of its many features.

The aperture f-stop setting and the shutter speed are inversely proportional, the larger the f-stop numbers (the smaller the aperture) the slower the shutter speed. The size of the actual aperture opening is directly related to shutter speed, the smaller the opening, the slower the shutter speed. The actual size of the lens aperture is inversely related to the f-stop numbers, the larger the numbers the smaller the opening.

The shutter speed determines how long the lens aperture remains open once the shutter release is tripped. The length of time that the lens aperture remains open is directly related to shutter speed, the faster the shutter speed the quicker the aperture shutter curtains open and closed. The length of time that the cameras sensor remains exposed to light is inversely proportional to the shutter speed setting, the higher the setting the less time the sensor remains exposed to light.

Shutter speed and lens aperture is directly related for any given lighting condition. If the ambient light remains constant and you increase the f-stop numbers by one full stop, the shutter speed will decrease by one full stop. The table below shows the relation ship between f-stop and shutter speed when the ambient light remains constant.

f-1.0 1/4000 sec

f-1.4 1/2000 sec

f-2.0 1/1000 sec

f-2.8 1/500 sec

f-4.0 1/250 sec

f-5.6 1/125 sec

f-8.0 1/60 sec

f-11.0 1 /30 sec

f-16.0 1/15 sec　

I haven't carried this table down to f-22.0, 32.0, 45.0, and 64.0 because it's not recommended that I try hand holding a camera below 1/60 second because of camera shake but this table should give you a good idea of what I was talking about. Each number in the f-stop column is considered one full stop, as is each number in the shutter speed column. One full stop is also referred to as 1 EV (Exposure Value.) here's a bit of photography trivia: we call f-stops stops because back in the film camera days, aperture settings and shutter speed settings were made by turning rings on the lens barrel. At each full stop, there was a notch that the ring clicks into, stopping it in the proper place for that aperture opening or shutter speed.

The easiest way to master the relationship between f-stop numbers and shutter speeds is to watch how one change in relationship to the other on your cameras LCD screen or in the viewfinder of a DSLR. When shooting in the "A" mode, watch how the camera adjusts the shutter speed as switch from one aperture setting to another. When shooting in the "S" Mode, watch how the camera adjusts the aperture as you switch from one shutter speed to another. Also, watch to see how the camera adjusts shutter speed and aperture settings when you switch to a higher or lower ISO setting. Simply put if you increase the ISO one full stop the effect is the same as opening the lens up one full stop or it has the same effect as shooting with a shutter speed one full stop slower.

I will expand further on what we have covered in this chapter when I cover metering modes in chapter two of The Basics of Digital Photography: metering modes and how to select the right metering mode to use. Until then practice the techniques we have covered in this chapter. I recommend spending one full day shooting in each of the modes that we covered in detail here, the aperture priority mode and the shutter priority mode, leave the full manual mode go until we cover metering modes in the next chapter because in the "M" Mode you will be selecting aperture, shutter speed, and ISO based on the meter reading that you will make.