A big advantage of using DSLR cameras is the ability to change lens. Different lenses serve different purposes and it’s important to pick the right lens for the right shot. There are many attributes of lens such as focal length, minimum focusing distance, aperture and others. Let’s get started with the most important of those – the focal length.

Focal Length

The focal length of a lens determines the magnification a lens provides for distant objects. A lens with a higher focal length magnifies the object more. The focal length is usually expressed in millimeters or mm. Full frame DSLRs have a sensor which has a diagonal of ~43mm. On such cameras, a 50mm lens is called a normal lens. Lenses with a shorter focal length like 18mm are called wide angle lenses, while lenses of longer focal length such as 200mm are called telephoto lenses. Wide angle lenses provide less magnification while telephoto lenses provide higher magnification. On cameras with smaller sensors, a lens with a smaller focal length provides the same magnification.

A telephoto lens will “zoom” into the object and magnify the object. A wide angle lens has a wide angle of view and makes the object a small part of the entire frame

Telephoto lenses are typically used to photograph wildlife or birds from a distance. They are also used for portraits. Wide angle lenses are often used in landscape photographs when one wants to capture the entire scene.

Zoom Lenses

Zoom lenses are lens with variable focal length. Zoom lenses can come in many ranges. You can get wide angle zoom lenses like a 10mm to 20mm or telephoto zoom lenses from 75mm to 300mm. Some manufacturers also build 28 to 200mm lenses. Zoom lenses provide the flexibility of shooting different kinds of photos without having to change lenses. However, this comes at the price of quality. In general, a fixed focal length lens, also known as a prime lens will have better quality than a zoom lens for the same price.

Speed/Aperture

The maximum aperture of a lens is another important thing to keep in mind while buying a lens. The bigger the aperture or opening of the lens, the more light it can let in. Since you can shoot with a higher shutter speed using lenses with a larger apertures, such lenses are known as fast lenses. The smallest end of the aperture range is usually useful when you want to take a long exposure even when there is lots of light.

Reading the Zoom, Aperture and Diameter of a Lens

Image Stabilization

Image Stabilization is a feature on some lenses. It helps to correct for motion blur caused by shaking of the camera while taking a photo with a slightly long exposure. Image stablelization helps to some extent, but don’t expect it to do magic. As a rough rule of thumb, maintain a shutter speed which is 1/focal length of the lens. For example, for a 18mm focal length, try to keep a maximum of 1/30th of a second exposure. Anything longer than that would cause a motion blur. With Image stabilization, maybe you could get the shot at 1/15th of a second, but definitely not at a 1 second exposure. Similarly, with the lens at 300mm, you’ll the the shutter speed to be at least 1/300th of a second.

Macro Lenses

Technically speaking, a macro shots is one where the subject is shot with a magnification such that the image on the sensor is as big or bigger than the subject in real life. So, it you are shooting a flower petal which is 10mm in length, it’s image on the sensor is also 10mm or bigger. This requires either than the lens have a very high magnification (like a telephoto lens) or that you go very close to the subject. However, every lens has a limit to how close you can get to the subject and still get it into focus. Macro lenses are lenses which allow you to focus a subject even when it is extremely close to the front of the lens.

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