Camera Lenses

Camera Lenses come in a variety of types and deciding which one to use is down to the types of objects in your images and the amount of time you have to shoot them.

Although there are different types of camera lenses, they all perform the same basic function: they capture the reflective light  from the subject and focus it on the image sensor . Where they differ is in the way they transmit the light.

Camera Lens Types

Most digital cameras have a fixed zoom camera lens that cannot be removed or replaced. One advantage is that the camera is sealed so no dust can get on the image sensor. On the other hank, digital SLR cameras have removable  lenses so you can change them as circumstances dictate.

Here are the main categories of camera lenses available :

Telephoto Lens

A telephoto lens is a lens with a long focal length that magnifies the subject. You can find this type of lenses called a telephoto, long focal length, long lens and zoom in but they all refer to the same thing - a lens that brings distant subjects closer. This is especially useful when you cannot get close to your subject— or you prefer not to.

Because of this property telephoto lenses are ideal for sports photography as it allows the photographer to shoot subjects that are at great distances.

It is also typically used in wildlife photography, as getting close to a subject might disturb it. The long focal length of the telephoto lens lets you keep your distance and still fill the viewfinder frame with the subject.

Telephoto lenses are also used by photographers who want greater control over limiting the depth of field (the area of an image in focus), typically in portrait photography.

When using larger aperture settings , combined with the long focal lengths of telephoto lenses, limits the depth of field to a small area (either the foreground, middle, or background of the image).

On the other hand using small aperture settings , together with long focal lengths, visually compresses space and makes objects in the foreground and background seem closer together than they actually are.

The primary drawback of a long lens is that most (but not all) such lenses have a smaller maximum aperture. This may force you to use a slower shutter speed. Also, since a long lens magnifies movement, just as it magnifies the subject, you may also have to use a tripod instead of hand-holding the camera.

Wide-Angle Lens

A wide-angle lens is a lens with a short focal length that takes in a wide view. This type of lenses can be called wide-angle, short focal length, short lens and zoom out but refer to the same thing - lenses that capture a wide expanse of a scene.

Wide-angle lenses are typically used when the subject is in the extreme foreground and the photographer wants the background in focus as well. This property can be used to create a dramatic effect and change the perspective in your images as objects very close to the camera loom much larger than those farther in the background.

Wide-angle lenses are thus ideal for photographing buildings, landscapes, interiors, and street photography.

When you are trying to shoot wide-angle images, it is important to know what is the image sensor size of your camera. If the image sensor is smaller than a frame of film, as many are, it captures a smaller area of the image, effectively increasing the lens' focal length by a factor of 1.5 x or so compared to the focal length indicated on the lens. For example, if your digital image sensor is 24mm, to achieve wide-angle view you need a lens with a focal length of less then 24mm.

The following table provides a overview of what focal lengths are required to be considered a wide angle or telephoto lens, in addition to their typical uses.

Lens Focal Lengths*	Lens Type	Photography Type
Less than 20mm	Extreme Wide Angle	Architecture
21mm - 35mm	Wide Angle	Landscape
35mm-70mm	Normal	Street and Documentary
80mm-135mm	Medium Telephoto	Portraiture
135mm-300mm	Telephoto	Sports and Wildlife
Greater than 300mm	Super Telephoto	Wildlife

*Note that the lens focal lengths are for 35 mm equivalent cameras. If you have a compact or digital SLR camera, then you likely have a different sensor size. To adjust the numbers for your camera, apply the appropriate lens multiplication factor.

Zoom Lens

A zoom lens has the mechanical capacity to change its focal length. A zoom lens can be extremely convenient, because many zoom lenses can change their focal lengths from wide-angle to standard and from standard to zoom. This eliminates the need to carry and change multiple lenses while shooting a subject or project.

One of the real advantages of using a zoom lens with an SLR camera is the fact that any changes in focal length, depth of field and image size  are all accurately seen in the viewfinder, thanks to the SLR camera's optical system.

Zoom camera lenses come in three varieties:

• An optical zoom actually changes the amount of the scene falling on the image sensor. Every pixel in the image contains unique data so the final photo is sharp and clear.

• Digital zoom, found on many fixed lens cameras, is produced by digitally increasing the size of the center portion of the image by adding new pixels to the image using interpolation. The interpolated image does not have as many unique pixels as one taken with an optical zoom so is inferior.

• Cropping zoom, called Smart Zoom by Sony, is just like digital zoom but it does not inflate the cropped image by adding pixels. It just uses some of the image sensors pixels to record an image and has exactly the same effect as cropping a picture in a photo-editing program.

Because of the movement between focal lengths , the f-stops are not always entirely accurate when using zoom lenses which is one of the major drawbacks of this lens type. To achieve a greater level of accuracy with apertures, many manufacturers have multiple minimum aperture values as the lens moves from a shorter focal length to a longer one. This makes the lens slower at longer focal lengths.

In addition, a zoom lens requires additional glass elements to correctly focus the light at different focal lengths. (It is desirable to have the light pass through the least amount of glass in order to obtain the highest-quality image possible) This makes zooms camera lenses generally be bigger and heavier than normal fixed focal length types.

Prime Lens

A prime lens , also known as a fixed lens, has a fixed focal length that is not modifiable. Prime lenses often have wider maximum apertures, making them faster. Wider apertures allow for brighter images in low-light situations, as well as greater control over depth of field.

Fixed lenses are primarily used by portrait photographers.

Marco Lens

Marco lenses or lenses with a macro mode are used for close up photography of insects or flowers. They have similar properties to a normal lens, but they are able to focus a lot closer to the subject. Macro lenses can produce images at a 1:1 ratio.

This is the universally accepted icon for macro mode.

The camera lenses with the longer focal lengths come in very handy for taking close ups of subjects that might otherwise be scared away. The optical quality of a macro lens is normally very high.

Fish-Eye Lens

Fish-eye lenses are at the fringe of wide angle lenses and offer a distorted perspective of the scene so that objects are magnified in the center and diminish in size and clarity in all directions in proportion to the lens' shape.

Their angle of view is typically a full 180% but some fisheye lenses produce an even greater field of view (as much as 220 degrees in some cases). Some would consider the distortion an error, but others would see it as art.

Lens Accessories

If your camera has a fixed lens, you may be able to use lens converters to decrease or increase its focal length. There are two popular accessories for cameras with interchangeable lenses. Both fit between the lens and the camera body.

• Extenders extend the range of the lens. For example, a 2x lens converter will make a 100mm lens into a 200mm lens.

• Extension tubes are used to increase magnification in macro close-up photography.

Considerations When Buying a Lens

The major things you need to consider when buying a lens fall into four categories:

• The optical quality of the lens: The better the lens, the better it can capture - resolve - fine details. In most cases, the optical quality of digital camera lenses go hand in hand with the price of the camera and the resolution of the sensor. At higher price levels, camera lenses have better-quality optics, which are necessary to keep up with the detailcapturing capabilities of higher megapixel image sensors.

• The speed of the lens: A lens' speed is determined by the maximum amount of light the lens is capable of transmitting—the largest f-stop value. Some camera lenses can capture larger amounts of light than others, generally because they have a greater diameter that can transmit more light. Think of a 1-inch-diameter pipe and a 2-inch-diameter pipe and visualize how much more water (or light) the wider pipe can conduct.
  
  Lens speed, in part, controls how low of a light level you can take pictures in and separates lenses into two categories - fast and slow. Fast camera lenses allow photographers to shoot at higher shutter speeds in low-light conditions. If you take many pictures in dim light, you will want a faster lens. For example, camera lenses with maximum f-stop values between 1.0 and 2.8 are considered fast

• The focusing range of the lens: The minimum focus distance of a lens determines how close you can get to a subject. If too close, the image will be blurry. Some camera lenses can focus closer than others. The ability to get up-close and personal with your subject can be very important in some types of photography.

• The magnification range of the lens: The zoom range determines how much or how little of a particular subject you can include in an image from a particular shooting distance. You might be able to take your basic image and double it in size (a 2:1 zoom ratio), triple it (a 3:1 zoom), or magnify it 12X or more (a 12:1 zoom). As you might expect, the ability to zoom enhances your creative options significantly. At the widest settings (wide-angle settings), you can take in broad sweeps of landscape, whereas in the narrowest view (telephoto), you can reach out and bring a distant object much closer.

Deciding What Lens to Use When

A normal (or "standard") lens for a 35mm camera usually refers to a fixed focal length lens of 50mm or a zoom lens zoomed in a little from its widest angle. The reason it is considered a standard lens is because a 50 mm lens is accepted as making the images of objects at different distances in a scene appear in about the same proportions as seen in real life.

Using a longer focal length lens (telephoto), everything appears closer than it actually is.

With a shorter focal length lens (wide-angle), everything looks farther away.

A normal-focal-length (50mm) lens is not necessarily the one photographers normally use. Deciding what camera lenses to use comes down to the types of objects in your photographs and the amount of time you have to shoot them.

• Shooting in low lighting conditions: The maximum apertures of f/3.5 to f/4.5 in the basic camera lenses are much too "slow" to be useful in low light levels. When shooting in such conditions, you will be looking to use zoom lenses with maximum aperture of f/2.8 or selecting a fixed focal length lens with an f/1.4 to f/2.0. You can invest in 28mm, 30mm, 35mm, 50mm, or 85mm f/1.4 lenses that can shoot under very dark conditions.

• Shooting sharper images: If you are after sharper images, you can often get better results with a special lens that was designed to produce sharper images. You might look into buy a close-up lens that is optimized for macro photography and produces especially sharp images at distances of a few inches or so.

• Shooting wider angle scenes: Using a wide-angle lens lets you take in a broader field of view, which can be useful when there is not enough room to move farther away from your subject.

• Shooting farther away: A telephoto lens lets you bring distant objects that much closer to your camera and makes it especially useful when you cannot get close to your subject.

• Shooting closer: An interchangeable lens you buy may be able to focus on subjects a lot closer to the lens, giving you valuable close-up or macro capabilities.

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