Basic Photography Article -#1 Exposure
I was asked to write a series of articles on some of the basics of photography for the PSC. So first I'll take a look at exposure, camera modes and camera controls over the next few articles. Then we'll move on to issues of sharpness, composition, lenses, and any other topics that I get requests for.
To make these articles as useful as possible, I'm including practice exercises at the end of each article.
How and why do we practice? First, I want to talk about a basic approach to improving your photography (or just about anything for that matter). There seems to be an amazing overlap between music and photography, so I'll use some music analogies to illustrate some ideas.
When I was in the school Jazz Band our director told us "If you're not happy with your playing, look at how you're practicing." If you're a musician, you practice scales, chords, and progressions. If you're a drummer, you practice rudiments, beats, time signatures and creating a groove. The purpose of practicing these basic skills is so that you can use them in performance without having to think about them. It's not always fun or exciting or glamorous, but it's necessary. Then you put these basics into practicing actual pieces of music. It is worth noting that practice involves repetition to learn specific skills. It doesn't mean just learning a couple of things that you enjoy and repeating that forever. There is a big difference between playing around and practicing, just as there's a big difference in practicing photography and just shooting. It means working on specific skills that you may not enjoy, but you know are necessary in the long run. Once you have those skills down, then performances follow, and then your performances hopefully get better and better. Eric Clapton or Mark Knopfler make playing guitar seem effortless. What you don't see are the countless hours they spent in a basement practicing the basics like scales, chord progressions and fingerings.
When Doc Severinsen, who is one of the world's best trumpet players was asked about practicing he replied " I practice at least two hours a day, because somewhere out there there's a kid practicing four hours a day so he can be better than me." This is in addition to his actual playing. So it is with photography. We practice to master the basics so we don't have to think about them when we are trying to create a picture that fits our vision. And none of us ever gets so good that we don't have to practice, at least not if we hope to keep getting better.
While we're at it, let's also talk about the difference between studying and practice. You can (and should) study by reading books, watching videos, and going to seminars on photography. But by themselves, these won't make you a better photographer any more than reading a book on guitar technique or watching an old Cream video makes you Eric Clapton. But if you take the concepts that you study, and actually pick up your instrument (whether it's a guitar or a camera) and physically practice using those concepts, then you will see your skills start to development. So, with these first few articles I'm going to give you some practice assignments to work on, so that you can use the basic skills to create better pictures.
And lastly, let's mention equipment. My band director didn't say go out and get a better instrument. Give Eric Clapton a cheap, basic guitar and he still plays like Clapton. Give Eric's guitar to a beginner and he won't suddenly sound like Clapton. It's easy to get excited about newer, better and more expensive camera gear (boy do I know about this), but it's not the camera that takes the picture. Sure, better gear makes it more convenient, maybe extends the possibilities, or helps you create a unique look, but without your skills, a camera is just an expensive box. So, the next time you tell yourself "I want to be a better photographer", think about what you need to practice and how you will practice, and plan to set aside time for practice.
The Exposure Triad
There are three basic things that control your photograph's exposure - aperture, shutter speed and ISO. We'll look each one, and then look at them in much greater depth in following articles.
Aperture is how wide the opening that lets through to the sensor (or film) in your lens is. The smaller the numerical value, the larger the opening is and the more light is allowed to pass through the lens. The larger the numerical value, the smaller the opening is and less light is allowed to pass through the lens. One term we use to describe the quantity of light is "stops". A change of 1 stop means we either double or half how much light passes through the lens. So for example at f/2.0 the lens allows twice as much light to pass through as it does at f/2.8. At f/4 only half as much light passes through as at f/2.8. The scale below shows whole stop intervals. Most digital single lens reflex cameras (DSLR's) and even many point and shoot cameras allow for an infinite adjustment between whole stops.
Lenses are often described in terms of their maximum aperture. A lens with a maximum aperture of f/2.8 lets in twice as much light when it is wide open as a lens that has a maximum aperture of f/4. The wider aperture can be useful in low light situations, but the trade off is cost. The wider the aperture, the higher the cost. You will see some zoom lenses that have two aperture values such as f/4-5.6 and are called variable aperture lenses. What this means is that the maximum aperture is wider at the short end of the zoom range than at the longer end. The reason is that it is easier and less expensive for the lens manufacturer to create a variable aperture lens. You can buy fixed aperture zoom lenses, but be prepared to spend (much) more. Once you move past the maximum aperture, there is little real variation in exposure between variable and fixed aperture zooms.
Besides controlling how much light passes through the lens, aperture or f stop has very important effects on the look of your photo, due how it affects depth of field, which is the area of a picture in acceptably sharp focus. That will be the subject of the next article in the series.
Shutter speed is how long the shutter is open, allowing light to strike the sensor (or film). The longer the shutter is open, the more light reaches the sensor. Doubling the time or cutting the time in half, changes light by one stop. Besides controlling exposure, shutter speed has major effects on how camera movement affects sharpness due to camera movement, and how subject movement appears in your picture. I'll cover shutter speed in the third article.
ISO is a measurement of how sensitive the sensor (or film) is to light. The higher the ISO number, the more sensitive the sensor and the less light it takes to create a good exposure. High ISO's allow faster shutter speeds or smaller apertures. The trade off is in image quality. Higher ISO's have more noise (or grain, if you use film), and generally less contrast and color saturation. But sometimes high ISO's are the only option for getting usable pictures in low light conditions. In general, you will want to select the lowest ISO that gives you the combination of aperture and shutter speed you need. Modern sensors are much more sensitive than film ever was. A huge advantage of digital over film is that we can change our ISO as light conditions change. With film, we would have to change to a different type of film, and sacrifice part of a roll if we hadn't used it all. As a result, many serious or pro photographers carried multiple bodies with different film in each.
A quick word on camera meters
I'll discuss metering in a later article, here is an introduction. Camera meters measure the light reflected from our subject into the camera. Initially camera meters just averaged all of the light entering the camera and adjusted the exposure so that the overall exposure would create a middle gray, which was what the "average scene" needed. But if your subject is predominately white or light colored, it will be reduced to a middle gray and be under exposed. If your subject is predominately black or dark, the camera will increase exposure to make it a middle gray and it will be overexposed. Likewise a bright background, bright back lighting, or a dark background may fool your meter. Modern cameras have gotten much smarter and have metering modes that try to correct for some of these situations, but they aren't foolproof.
As you're shooting, take a quick look at the camera's LCD and see if the exposure is too light or dark and make adjustments. If your exposure is too dark, you can dial in a "+" compensation or if it is too light you can dial in a "-" exposure compensation.
How the three controls combine for exposure
Proper exposure depends on the right amount of light hitting the sensor and the sensitivity of the sensor. So we can make the sensor more sensitive by setting a higher ISO, and it takes less light to make an image. If we decrease the ISO it takes more light. Slower shutter speeds allow more light to reach the sensor, but may cause blurring due to camera or subject movement. Higher shutter speeds allow less light to hit the sensor. We can adjust for that with wider apertures, higher ISO's or a combination of the two. Larger apertures (lower f numbers) allow more light to hit the sensor and we can use faster shutter speeds and/or lower ISO's. Smaller apertures allow less light to reach the sensor, but provide great depth of field. We can adjust by using slower shutter speeds or higher ISO, or a combination of the two.
If you have been following all of this, you will realize that we can get a correct exposure with any number of combinations of shutter speed, aperture, or ISO as in the chart below. So, which is the right combination, if they can all give a "correct exposure"? That's where your vision as a photographer comes into play. Is there subject movement and how do you want to show it? How much depth of field do you want? How steady can you hold the camera and at what shutter speeds do you see softness caused by camera movement? It's why two photographers can stand shoulder to shoulder, shoot the same subject, get good exposure, but very different looking pictures.
All DSLR's and even most point and shoot cameras have a number of exposure modes that you can select. The major difference in the modes is in which of the exposure controls you set, and which the camera sets.
Program-Generally you set the ISO, and the camera sets the shutter speed and aperture. It usually tries to maintain a fast enough shutter speed for handheld shooting, but that may not always be possible. Some cameras have a totally auto program mode where the camera controls ISO, shutter speed and aperture. Program modes are best when you need your camera to ready quickly to take a shot, but you don't care about having any creative control. Think of it as snapshot mode.
Aperture priority- You set the aperture and ISO and the camera sets an appropriate shutter speed. This is the mode to use when you want control over depth of field. Be aware of shutter speed as it may drop too low to handhold reliably.
Shutter Priority- You set the shutter speed and ISO and the camera selects an appropriate aperture. This is the mode to use when you want control over how motion is depicted. Fast shutter speeds to freeze action, slow shutter speeds for panning or blurring motion. Manual-You set ISO, aperture, and shutter speed. There is an exposure indicator in the viewfinder to show when you have set a correct exposure. This is the setting you would use with studio flash, or in light conditions that aren't changing rapidly and you want total control.
Practice Exercises - Reading this article was your "study". Now to really learn how to put this into use it's time for practice.
1) Get out your camera manual practice selecting aperture priority, shutter priority, program and manual modes. Practice adjusting aperture and shutter speeds. Learn how to change ISO and how to dial in exposure compensation.
2) Put your camera in aperture priority. Look through your viewfinder, set a wide aperture and notice the shutter speed the camera selects and shoot a picture. Set increasingly smaller apertures and notice how the shutter speed changes and shoot a picture at each aperture. Repeat the process at increasingly higher ISO's.
3) Put your camera in shutter priority. Look through your viewfinder, set a fast shutter speed and notice the aperture the camera selects and shoot a picture. Set increasingly slower shutter speeds and notice how the aperture changes and shoot a picture at each shutter speed. Repeat the process at increasingly higher ISO's.
4) Choose either aperture or shutter priority mode, go outside and photograph a scene. Now set your exposure compensation at -2 and reshoot the same scene, Repeat at -1, +1 and +2 compensation.
5) Always remember to turn exposure compensation back to"0" when you no longer need it.
6) Return your ISO back to a usably low setting after using very high ISO.
Some photographers recommend keeping your camera manual in your camera bag. That's not a bad idea, since there are always things I don't do often enough to remember without referring to the manual. If you are like me, it's also a good way to lose your manual. Almost every manufacturer allows you to download your camera manual in PDF format. You can then save that on your phone, and it's always available.