The Camera Lens How to Find the Right Lens?

The possibility to change the lens is one of the main assets of the SLR digital cameras and hybrids. The user adapts it according to the cliché that it wants to achieve. This apparent flexibility is not without consideration: the objectives are bulky and expensive. Our tips on how to choose.

According to a2zcamerablog, SLRs and hybrid cameras are often delivered in kit with a versatile lens that will suit most users. But as soon as the photographer develops specific needs (picture animal, sports, portrait, etc.), it must adapt its equipment with the objectifadequat.


Focal Length And Opening

A goal is characterized by its focal length and its opening. The focal length, expressed in millimetres, determines the scope of the purpose associated with a given sensor. The opening reflects its brightness, which is the amount of light that enters the lens. It is indicated by numbers behind an “f” on the lens (f/1, f/1.4, f/2, f/2.8, etc.). Opening decreases as the number increases. It also determines the depth of field (sharpness of the photo area).

Equivalent Focal

The angle of coverage depends on the focal length, i.e. the distance between the sensor of the camera from the optical center of the lens. But it also depends on the size of the sensor of the camera. All cameras were operating with a 35 mm (24 × 36 mm) film. But in digital, the sensor size is not standard. The manufacturer of a goal doesn’t know in advance the size of the sensor of the device on which it will be used. So that the user is located, it indicates the focal length in 24 × 36. Each device has a coefficient with which one must multiply this focal length to get the equivalent focal length. It is 2 at Olympus and Panasonic, Canon 1.6, 1.5 at Nikon, Sony and Pentax. So a 50 mm on a digital Nikon or Pentax fit as a 75 mm on a film.

The Great Families Of Objectives

A standard lens is the angle of human vision; its focal length (in equivalent 24 × 36 mm) is 50 or 55 mm. It is suitable for ‘family’ use (vacation photos, group, etc.).

A telephoto lens has by definition of a long focal length (85 mm, 135 mm, 200 mm and more). More focal length gets longer, more the field covered by the objective is limited and the captured area reduced. It corresponds to an angle of vision less than the human eye. We use this type of goal to take portraits or distant details.

Conversely, a lens wide angle is short (less than 30 mm) focal length. It allows to cover wide angles of vision, and therefore is well suited to the shooting of landscapes. Some objectives to photograph on 180 °; These are the fisheyes (“fish eye”) whose focal length is usually 15 or 16 mm, sometimes less.

Finally, macro lenses allow to photograph very close to tiny subjects (flowers, insects, etc.).

Focal Length Fixed And Zoom

The objectives lens offer no magnification factor. The photographer must get away or move closer to his subject to change the captured area.

Zoom lenses allow, them to vary the focal length on a specific range (18-200 mm, 70-300 mm, etc.). Therefore, they are more versatile.


The objectives of a mark are generally not compatible with other devices: each manufacturer offers his own mount. Zoom Nikon cannot be fixed on a Canon camera, etc. There are however certain cases of rings that allow to adapt them. But they prevent some automatisms, such as autofocus operation.

Some manufacturers, such as Sigma or Tamron, propose objectives compatible with the devices of different manufacturers.

Focus Distance

All objectives specify the minimum distance to which to find a topic to be able to point on it. This distance is very variable from one goal to another, from a few centimeters to several meters for large telephoto lenses.


A 50 mm fixed lens weighs about 300 grams, the weight of a telephoto lens can easily reach several pounds. As say, a goal knows not to be forgotten. As soon as the photographer uses dedicated targets, he forced himself to carry heavy equipment. He must also stay in bags adapted (with reinforcements of protection) expensive.