Since the camera was invented people have been relying on it to preserve their special events. When I was a kid our Kodak Brownie sat in at all holidays, attended all birthday parties, and tagged along on summer vacations.
The majority of the shots were candid, but if it was a staged photo, the “ceremony” was always the same. Mom would line us up. Dad would look not at us but down through the viewfinder and he just might motion for us to get closer together, or ask us to change places. When the scene was to his liking we’d get the signal, “Say Cheese.” We’d look into the Brownie’s big round eye, smile our brightest smile and in a flash, the moment became part of family history.
Today, picture-taking is an everyday occurrence. People snap anything and everything with their Smartphone. Digital cameras, the more megapixels, the merrier, are popular too but in most cases are saved for special occasions; although their sleek compact size makes them as easy,if not easier, to stow away in a pocket.
As recently as the 90′s that pocket might have held an extra roll of film because no one wanted to chance being at Cousin Suzie’s wedding or Junior’s graduation and find she only had one exposure left on the roll. Today the pocket is available because the image sensors in today’s cameras have done away with the need for film (as well as the need for a trip to the drugstore to drop off the film).Image sensors have made every moment “a Kodak moment” as they used to say. (Kodak, anyway)
The Lens as Eye
One thing has remained constant though – the lens smack dab in the middle of the camera, and my childhood vision of the lens as being the eye of the camera turned out to be an apt analogy. In the center of the human eye is the pupil which dilates to admit light to the retina, allowing the eye to focus. In the middle of the lens is the aperture, whose shutter opens and closes to regulate the light which in the old days fell on the film plane, but now on the image sensor.
If we are to understand lenses there are a few terms we need to know. And in order to understand them, we need to be wearing our math caps.
Field of View
Field of view refers to both the area we include in our image and the degree of detail we wish to see. Determining a field of view is different with different cameras. It depends primarily on the focal length of the lens and the size of the camera’s image sensor.
The focal length as its name suggests has to do with the distance from the camera to the objects included in the field of view. It is also determines the amount of magnification. A picture taken from a greater distance needs more magnification. The longer the focal length of a lens, the more magnification it supplies.
The focal length is expressed in millimeters (mm). We’d choose a lens with a higher focal length (higher mm) for a scene taken from a distance since we would need a degree of magnification. Conversely if the object is closer we would use a shorter focal length (less mm) since we do not need much magnification.
Angle of View
The angle of view is linked to the lens as well. When using a lens of longer focal length (more magnification) we narrow our angle of view; and when using a lower focal length (less magnification) we widen the angle of view.
Lenses are classified by their angle of view, and this is determined by the relationship of the focal length to the diagonal measurement of the image sensor:
If the angle of view is about 50 degrees and its focal length is equal to the diagonal measure of the sensor it is classified as normal
If the angle of view is wider than 60 degrees and the focal length is shorter than the diagonal sensor, it is classified as wide angle and is used for close-up objects.
If the focal length is longer than the diagonal measure of the sensor, the lens is long-focus and is used for objects farther away. A telephoto lens is the most common form of long focus lens and uses special optical configurations to give the effects of a shorter lens.
Also known as the F-number, this term applies to the lens’ aperture, and governs how much light will be admitted to the image sensor. The f-stop, like the angle of view, depends on the focal length for its determination. We arrive at the f-stop by dividing the focal length by the size of the aperture.
Lenses with a smaller f-number have a wider aperture and a slower shutter speed, and since they admit more light, are the choice for low light conditions. The opposite is true for larger f-numbered lenses. Their apertures are smaller and let in less light, thus they have a faster lens speed. Besides being good in well-lit areas, they add field depth.
And so, although times have changed, with image sensors replacing film as the repository for light, the lens is still a force to be reckoned with – and that reckoning calls for mathematics.
Kintronics, Inc has expert knowledge of IP cameras. They don’t just sell surveillance cameras they listen to their customers, question them and learn the whole picture before recommending a surveillance system to fit their need. Customers include the military, hospitals, federal, state, and city governments, educational institutions as well as individuals and small businesses wishing to secure their premises.
Call Kintronics at 800-431-1658 or visit the website http://www.kintronics.com to fill out a request information form