Lens Types

Although there are many varieties of lenses, common lens types include telephoto, wideangle, zoom, and prime. All of these lenses perform the same basic function: they capture the reflective light from the subject and focus it on the image sensor. However, the way they transmit the light differs.
Note: Although there are several subcategories and hybrids of these lens types, these are the most basic.








Telephoto

A telephotolens is a lens with a long focal length that magnifies the subject. Telephoto lenses are typically used by sports and nature photographers who shoot their subjects from great distances. Telephoto lenses are also used by photographers who want greater control over limiting the depth of field (the area of an image in focus). The larger aperture settings, combined with the long focal lengths of telephoto lenses, can limit the depth of field to a small area (either the foreground, middle, or background of the image). Small aperture settings, combined with long focal lengths, make objects in the foreground and background seem closer together.


Wide-Angle

    A wide-angle lens is a lens with a short focal length that takes in a wide view. Wideangle lenses are typically used when the subject is in the extreme foreground and the photographer wants the background in focus as well. Traditionally, the focal length of a wide-angle lens is smaller than the image plane. However, in the digital photography age, the sizes of image sensors vary, and the lens multiplication factors of most DSLRs increase the focal length. Check the specifications of your camera to ascertain the size of your digital image sensor. If the size of your digital image sensor is 28 mm, you require a lens with a focal length less than 28 mm to achieve a wide-angle view.

Zoom

A zoom lens, also known as an optical 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. However, because of the movement between focal lengths, the f-stops aren’t always entirely accurate. 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. (See “Understanding Lens Speed” on page 15 for an explanation of lens speed.) Plus, 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.
Prime
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. For more information about lens speed, . Wider apertures allow for brighter images in low-light situations, as well as greater control over depth of field. Prime lenses are primarily used by portrait photographers. For more information on depth of field


Understanding Digital Zoom
The digital zoom feature offered by some camera models does not really zoom in
closer to the subject. Digital zoom crops into the center area of the captured frame, effectively enlarging the pixels. This results in a picture with a lower overall image quality. If you don’t have a telephoto or optical zoom lens and you want a close-up, physically move closer to the subject, if you can.


Understanding Lens Multiplication with DSLRs
Most interchangeable lenses were originally created and rated for the 35 mm film plane of traditional SLRs. If you compare the area of a 35 mm film plane with the area of most digital image sensors’ image planes, you’ll see that the area of most digital image sensors is a bit smaller. The focal length of a lens changes when it is put on a DSLR with a digital image sensor smaller than 35 mm. This smaller image plane effectively increases the focal length of the lens because more of the image circle coming out of the lens is cropped. For example, if you put a 100 mm lens on a DSLR that has a 24 mm digital image sensor, the focal length of the lens is multiplied by a factor of approximately 1.3. A 100 mm lens with a 1.3x multiplication factor effectively
becomes a 130 mm lens (100 mm multiplied by 1.3). Another reason to take lens multiplication into account is that shooting wide-angle images becomes increasingly difficult when using cameras with smaller digital image sensors. For example, if your digital image sensor is 24 mm, you require a lens with a focal length less than 24 mm to achieve a wide-angle view. Check your camera specifications for the size of your digital image sensor.