Welcome to the second article in the "How the Heck Does it Work" series. If you missed the last newsletter, let me explain my purpose in writing. I am one of those people who has a general idea of how certain technical appliances work.
Ok, Ok, for the sake of honesty, it's a fuzzy idea of how they work. OK! OK! OK! I usually feel like my brain is going to explode whenever I talk to an engineer. But I think I've figured out my problem. Like a house whose walls start to crack, my understanding is built on a very shaky foundation. It needs that strategically placed beam to shore it up. I suspect I am not the only one wandering around the world in this condition. And so this article is offered as a beacon to other "Sort of lost" souls. Come with me, as we seek understanding.
In this article I'd like to describe surveillance cameras. But, you know what? I'm not ready. You know why? I don't understand cameras - at all. I'm the type who never takes a camera on a trip. I figure Why bother? My friends always get duplicate copies of their photos.
As I sit here at my computer, trying to decide where to start, I find myself staring at the blank screen. My vision gets blurry, my eyes lose focus. And voila! I realize - That's it - focus, eyes , the eye of the camera - the lens. It has something to do with focus, doesn't it?
The earliest cameras did not use lenses. Leonardo da Vinci discovered that light passing through a small pinhole could project an image, the smaller the pinhole, the sharper the image. This camera obsura, as it was known, was the Nikon of the 17th century.
In 1826, a Frenchman named Joseph Niepce discovered that silver chloride could be used to make bitumen sensitive to light. Thus, images could be formed within the camera. But how can we control the light that gets to the film? Too much can be a bad thing.
What is a lens? Simply put, it's a piece of glass that serves two purposes. It lets us have a large hole to let in a lot of light and it allows us to focus light in an intended spot for the projected image. The bigger the lens, the more light can get in. But like a big powerful dog, it needs a strong handler. It needs two of them: the aperture and the shutter.
The aperture is a leaf-like piece of metal within the lens. It controls the size of the hole through which the light enters, thus determining how much light enters the camera. The shutter controls when light will enter and for how long. We will discuss how these two work together a little later in the article.
It could be said that the lens is the most important component on a camera. It is what allows you to get clear, focused shots amidst a clearly defined background. There are a number of lenses to choose from: normal, wide-angle, telephoto, and zoom. The normal lens will give the perspective most like that seen with the eye. A wide-angle lens broadens the perspective and comes in handy when you cannot back up to get the whole scene in. A telephoto lens, as its name implies, brings the image closer while narrowing the perspective. A zoom lens lets you dwell in all these worlds, offering a range which stretches from wide angle through normal and into telephoto. Having provided this simple explanation, I feel emboldened. I think I'm brave enough to delve into why these lenses are able to give us such different results. But I warn you, the f-word is involved, in fact, two of them: f-stop and focal length.
Focal length is defined as the distance between the lens and the point of focus. When using a standard 35mm camera, this point of focus will be the film (or in a digital camera, the image sensor). When this distance is about 50 mm, the image appears much as it does with our normal vision. 50 mm is the focal length of a normal lens.
As focal distance of a lens decreases to less than 50 mm, the angle of view grows larger, or wider. This is the wide angle lens. With a wide angle lens, the depth of field gets better and focus becomes less important. But the wide angle lens gives a distorted perspective. Objects close to the camera look much larger and closer than they really are. Conversely, objects far from the camera appear smaller and farther away. Sound familiar? That writing on the sideview mirrors of your car. “Warning, Objects seen in this mirror are closer than they appear." Those mirrors are wide angle mirrors. Try looking at your face close up.
Then, there's the telephoto lens. Time for reader participation - if the normal lens is 50 mm, and the wide angle is less than 50 mm, the telephotos must be.... that's right! It's greater than 50 mm. A telephoto lens focuses on a small central portion of the scene, magnifying that image. Like the wide angle, the telephoto distorts the perspective, objects seem to have less space between them. This effect is called compression. In contrast to the increased depth of field of the wide angle view, the telephoto, gives a very shallow depth of field, putting the background out of focus.
Nothing is exact, but you will be safe in assuming that if you use a lens with a focal length within the 50-55mm range, you will have a normal view, anything within the 18-35mm will result in a wide angle, and within the 80-500mm, a telephoto shot.
Enough! Remember, this is the simple section of the newsletter. But there is one more thing to consider, focus. And, for that, we need to know about speed control. No, not traffic lights, or speed bumps, I'm talking about apertures, shutter speeds and f-stops.
If you'll recall, the aperture controls how much light enters the camera. We also use it to control the depth of field of the image, how the background will look. If the background is ugly or distracting, we might want to make it less noticeable, to distract the eye with a softer focus. The aperture is the tool. When there is very little light we open the aperture to allow more light in. This reduces the depth of field so some objects may appear out of focus. Think of how some drivers suffer from night vision after dark. Objects far away are out of focus because their depth of field is compromised.
Conversely, if you want a clear sharp background, you need a deep focus. You need more light. Then you can close down the aperture and increase the depth of field. More things will be in focus. Think of how sharp everything appears on a crisp clear winter morning. Everything stands out, doesn't it? Are you with me so far? Good. The aperture isn't a lone agent it works hand in hand with the shutter.
Shutters can be set at a fast speed or a slow speed. A fast setting opens and shuts quickly, letting in only a small amount of light. A slower setting obviously is open longer, allowing more light to enter. Why is this important? The longer the shutter is open, the more likely motion will occur, blurring the image as it travels across the exposed film. In this case a fast setting is needed. But will the image suffer from this reduced light? Not if the aperture is set correctly. It needs to be open wide to counteract this, to permit more light to enter in a shorter time. In cases where the shutter is set at a slow speed, letting in more light the aperture must have a narrower opening or the film will be over exposed, resulting in a light fuzzy image.
So you see the relationship of the aperture and the shutter is one of partners at odds, but still working in sync. As with any type of relationship, each partner needs to know their boundaries. So do we, thus the need for understanding the controls and the numbers involved - the shutter speeds and the f-stops.
Bear with me please, I'll make this as simple as possible. I don't have any choice. Numbers are coming up, and when faced with numbers, my brain is in danger of exploding. The aperture can be adjusted, the larger the opening, the more light allowed inside. But also bear in mind that the larger the opening, the less sharp the final image will be. Aperture openings are identified as f-stops and measured at 1.4, 2, 4, 5.6, 8, 11, 16, 22, 32. Each is a fraction representing its ratio to the focal length of the lens, e.g.. 2 is 1/2 representing the ratio of the size of the aperture opening to the focal length of the lens. 32 is 1/32 the focal length. 8 is 1/8, and so on. Keep in mind that the numbers are deceiving, they actually decrease in size as they increase. Sigh, why do things have to be so complicated
1000, 500, 250, 125, 60, 30, 15, 8, 4, 2, 1
There they are, folks! Those are the speeds. HOWEVER -- It's not that easy,, like the F-stops, each speed is a fraction a second. So 1000 is 1/1000th of a second, 60 is 1/60th and 1 is a full second, etc. (Who thought up all of this?)
Nirvana: the secular definition as found in Webster's II New Collegiate Dictionary: "an ideal condition of perfect harmony and peace".
If we want a perfect picture, we need to reach image nirvana. We need the perfect balance between shutter speed and aperture setting. A fast shutter speed (high number) will let in a small amount of light. To counteract this, the aperture must be open wider (low number) to let in more light. And in the opposite case, if the aperture is set to let in a small amount of light (high number), the shutter speed must be slower (low number) to allow more time for the light to enter. The two work hand in hand, but coming from opposite directions. If one goes up to a larger setting, the other must come down if we want the same amount of light to enter.
Thanks Goodness in this day and age, almost all cameras have automatic settings, so we don't really have to think about it. But don't you feel smarter now that you know all this? I do!
If you would like to get smarter about our products, please contact us at 1-800-431-1658 or 914-944-3425.