|Posted by [email protected] on May 5, 2016 at 1:20 AM|
How to find the right target ?
The ability to change lenses is one of the main advantages of digital SLR cameras and hybrids. The user adapts according to the cliché that it wants to achieve . This apparent flexibility is not without its counterpart : the objectives are bulky and expensive. Our advice to choose well.
SLRs and hybrid devices are often delivered in kit with a versatile lens that will suit most users . But once the photographer develops specific needs ( wildlife photography , sports , portrait, etc. ), it must adapt its equipment with the proper lens.
Focal length and aperture
A target is characterized by its focal length and aperture. The focal length , in millimeters, determined the scope of the objective associated with a given sensor . The opening reflects its brightness, that is to say the amount of light entering the lens. It is indicated by numbers placed behind an "f" on the lens (f / 1, f / 1.4 , f / 2, f / 2.8 , etc.). The opening decreases as the number increases . It also determines the depth of field ( sharpness of the picture area).
Equivalent focal length
The angle covered field depends on the focal length , that is to say the distance from the camera 's sensor of lens optical center. But it also depends on the size of the camera sensor. All film cameras operated with a 35 mm film (24 × 36 mm). But in digital, the sensor size is not standard . The manufacturer of a goal does not know in advance the size of the camera sensor on which it will be used . For the user mark, it indicates the focal length 24 × 36. Each unit has a coefficient by which multiply the focal length to obtain the equivalent focal length. It is 2 in Olympus and Panasonic, Canon 1.6 , 1.5 , Nikon , Sony and Pentax . Thus a 50 mm on a digital Nikon or Pentax he will fit as a 75mm on a film
The major targets families
A standard lens is the angle of human vision; its focal length (equivalent to 24 × 36 mm) is 50 or 55 mm. It is suitable for a "family" use (holiday photos, group, etc.).
A telephoto lens has by definition a long focal length (85 mm, 135 mm, 200 mm and more). The longer the focal increases, so the scope of the objective is restricted and reduced the captured area. It corresponds to a viewing angle of less than the human eye. this type of lens is used for taking distant details or portraits.
Conversely, a wide angle lens of short focal length (less than 30 mm). It can cover wide viewing angles, and is therefore well suited to shooting landscapes. Some lenses allow to photograph 180 °; it is the fisheye ( "fish eye") whose focal length is generally 15 or 16 mm, sometimes less.
Finally, macro lenses allow to photograph closely tiny subjects (flowers, insects, etc.).
Fixed focus and zoom
fixed focal objectives offer no magnification. The photographer must move away from or closer to the subject to change the captured area.
Zoom lenses allow the student to vary the focal length on a specific range (18-200mm, 70-300mm, etc.). They are more versatile.
The objectives of a trademark is generally not compatible with devices of another: each manufacturer offers its own beast. Nikon zoom can not be attached to a Canon camera, etc. However, there are some cases in which the rings can therefore be adapted. But they prevent the operation of some automations like auto focus.
Some manufacturers such as Sigma or Tamron, propose objectives compatible with devices from different manufacturers.
All lenses provide the minimum distance that must be a subject to be able to update it. This distance varies from one objective to another, from a few centimeters to several meters for large telephoto lenses.
Weight / size
A fixed lens 50 mm weighs about 300 grams, the weight of a telephoto lens can easily reach several kilos. Both say, a goal does not know how to forget. Once the photographer is using dedicated objectives, it is forced to carry heavy equipment. He will also stay in suitable bags (with protective reinforcements) expensive.