[nextpage title=”Introduction”]
The lens of a camera is truly the eye to the world in photography. It is the viewer through which the camera sees the shot you want to take. The lens is an essential element needed to take good photographs. So when you purchase a new camera, you should always check out the type and quality of the lens. Even a camera with a superior sensor and an adequate number of megapixels will not produce good photographs if the lens is of inferior quality.
Lenses can be made of glass or plastic or a combination of both. You will want to stick with glass lenses, if at all possible, since glass offers much better clarity. In fact, the lens is sometimes referred to quite simply as the “glass.”Small point-and-shoot, and mid-range cameras will come with a lens that is built into the camera. A digital SLR (Single Lens Reflux) camera will give you the ability to change the lenses and to use different lenses for different occasions. SLR cameras are sometimes available as a “body only” with no lens. Sometimes they come as a kit with one or two lenses to get you started. You can then purchase additional lenses as the need arises. The lenses for SLR cameras often cost more than the camera body itself. Truth be told, however, the lens, if handled correctly, will last longer than the camera itself. So most photographers look at the cost of lenses as an investment.Be aware that when you buy a digital SRL, you are basically buying into the line of lenses that will fit that particular camera. For instance, if you purchase a Canon camera body, you will need to use Canon lenses. The same is true of Nikon. Olympus uses lenses from Zuiko. One of the main differences is in the lens mount. This is the point of connection between the lens and the camera. Every manufacturer has its own type of lens mount. Some lenses manufacturers like Zeiss have different lines of lenses that will fit Nikon, Canon, and Samsung SLR cameras. They do this by creating each lens with the type of lens mount used by the different manufacturer. In some cases, digital camera lenses also have to coordinate with the size of the sensor. So a four-thirds camera may use different lenses than a full-frame digital camera.Lenses are created specifically for digital cameras. Those produced for 35 mm film cameras may mount on the bodies of a digital camera. However in most cases, the 35 mm lens is slightly larger and allows unwanted light into the camera body, causing an often unacceptable halo effect. Because most SLR sensors are smaller than the 35 mm format, there is usually also a cropping of the image when compared to the images from the film camera. These problems, in general are so severe that you will want to purchase lenses that were created specifically for a digital camera.There are several types of common lenses: wide angle, normal telephoto, prime, and zoom. In this tutorial we will cover some of the more important aspects of a lens, including the types of lenses, the lens focal length, and aperture.[nextpage title=”Focal Length”]
The focal length is an optical measurement that indicates how strongly the light converges or focuses. When parallel rays of light strike a lens focused at infinity, they converge to a point called the focal point. The focal length of the lens is the distance from the middle of the lens to that focal point. A simple way to think about it is that the focal length equals image distance for a far subject (infinity). To focus on anything closer than infinity the lens must be moved farther from the sensor. That is why the lens becomes longer when you turn the focusing ring.Simply put, the focal length is how much the camera can see. A focal length of around 50mm mimics what the human eye sees and gives the most “natural” view. A focal length of 35mm or less is considered wide angle which allows more of the subject to be seen. A focal length of 70mm or greater is considered telephoto with less of the subject showing. The table below put it in perspective.
|
Focal Length (35mm equivalent)
|
Lens |
| Less than 21 mm | Extreme wide angle |
| 21 mm – 35 mm | Wide angle |
| 35 mm – 70 mm | Normal |
| 70 mm – 135 mm | Telephoto |
| 135 mm – 300 mm | Extreme telephoto |
One other term that is common in photography and in lens descriptions is the f-number. Because of the letter “f,” you might think that this would refer to the focal length, but instead the f-number refers to the aperture of the lens as well as the focal length. The f-number is the ratio between the diameter of the aperture and the focal length of the lens. The f-number is usually written as something like f/8 which means the aperture diameter is 1/8th the focal length. It is often also written with a colon. So f/8 would be the same thing as 1:8.Aperture is another common photographic nomenclature. The aperture of a lens is the amount of light that the lens allows to reach the sensor. In SLR lens, the aperture is usually a range that indicates the smallest amount of light to the largest amount of light that the lens can open and/or close to accommodate. Contrary to what may seem logical to the amateur, larger apertures have lower f-numbers and smaller apertures have higher ones. Lenses with larger apertures are often referred to as faster because the shutter speed can be made faster for the same exposure. Smaller apertures mean that the objects can be focused over a wider range of distance which is also referred to as the depth of field.Here’s what you need to remember. Higher f-numbers have smaller aperture size, require slower shutter speeds and accommodate a wider depth of field. Lower f-numbers have larger apertures, require faster shutter speeds and have a narrower depth of field. The numbers you see on the side of a lens usually look similar to the Olympus lens shown in Figure 1. 14-42mm is the focal length. 1:3.5-5.8 is the aperture.
Figure 1: Markings on a Lens.
[nextpage title=”Types of Lenses”]
There are several different types of lenses. First there are two simple categories: prime and zoom.
A prime lens is one that has a fixed focal length that cannot be changed. Using a zoom lens, the photographer has the ability to vary its focal length within a predefined range. Since a zoom lens can give similar results to a telephoto or a wide-angle lens, they are very versatile and have become a standard in small point-and-shoot cameras. The zoom designations of 2X, 3x, etc. refer to the ratio between the longest and shortest focal lengths.Lenses are also categorized by the focal length. Those general categories are normal, wide-angle, and telephoto. Lenses are classified as normal lenses if they have a focal length of somewhere near 50mm. Since this mimics the average focal length of the human eye, it gives the most natural view. Wide angle lenses have small focal lengths and produce photos with elongated fields of view. Telephoto lenses have larger corresponding focal lengths. They make distant objects appear magnified. Different lenses like the wide angle and telephoto change the view. A wide angle lens makes distances seem greater than they really are while a telephoto lens makes far away objects seem closer than they are. Proper use of these lenses can greatly add to the photograph.Most small point-and-shoot and mid-range cameras today have zoom lenses. Some also have wide angle capabilities. Since you cannot change the lens on these smaller cameras, you need to check out the capabilities and quality of the lens carefully when you make your purch
ase.If you are purchasing a digital a SLR camera, choosing the camera body will be extremely important because that will determine which lenses you can purchase in the future. So you need to look at the quality and type of the available lenses. Sometimes several different lines of lenses are available. For instance, Canon has a line of average lenses and they also have an L-series which are more expensive because they have superior optical performance and professional quality construction.
When you purchase your first lens, you can’t go wrong with a normal lens with a good focal range. Later you can add other lenses, according to your needs.
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