The optical piece of equipment that sits in front of your camera is the single most important piece of gear that you own. It’s actually more important than the one that it attaches to – the camera. Ask 10 professional photographers what to do with the extra bit of cash that you are left with, after buying a camera and a kit lens and 9 out of them would suggest you to get a better piece of glass. The tenth one will suggest you sell off the kit lens to get a better lens!

What makes the lens so important? Well, simply put it controls light. Light gets focused after travelling through the lens barrel. The optical quality of the lens determines if there is going to be any aberrations (most do have in some quantities though). The lens also determines the angle of view as does the exposure settings that you can use.

This article might just be used as a buying guide for new lenses.But it is not intended as such. I would rather that you use this to get familiar with the lens that you own or the one that you intend to buy so that you can make better images.

Focal length

cannon lens

Focal length is the first determining aspect of a lens. It is denoted as a number such as 18mm, 24mm or 300mm. The distance in mm has nothing to do any sort of dimensional attributes. It denotes the distance between the point which is the optical center of the lens and the imaging media (sensor) when the lens is focusing at infinity. This is an optical mumbo-jumbo, this definition that is. However, all that you need to keep in mind is the focal length of the lens.

Focal length controls the angle of view of the lens. Angle of view means how much of the scene it is going to capture. Longer the focal length shorter is the angle of view. A 300mm f/2.8G ED VR II lens offers an angle of view of 8 ° 10’ on a full-frame Nikon DSLR. Conversely, a Nikkor 24mm f/2.8 lens offers an angle of view of 84 ° on a full-frame Nikon camera.

A lens that has a focal length of more than 50mm but less than 200mm is considered a short tele lens. Lenses such as the 105mm and the 135mm are widely considered as the best in the business for portraitures. Anything longer and it falls in the domain of proper tele-lens. Super tele lenses are those which are generally 300mm or longer.

On the other end of the spectrum are wide angle lenses. These are lenses which have a short focal length and consequently a wider angle of view. The widest among them are the fish-eye lenses such as the Nikkor 16mm AF f/2.8D. This baby can see 180 °, giving a true fish-eye perspective.


cannon tele lens

Another set of numbers and letters you will find on a lens reads like this f/2.8. This denotes the aperture f-stop. Speaking in a layman’s language aperture denotes the size of the opening at the front of the lens which lets light in. Aperture is denoted in f-stops. These can be expressed in full-stops or ½ stops or 1/3 stops.

The size of the aperture can be increased or decreased using a mechanical control operated via electronic connection through the lens mount. When the opening is increased we refer to it as a smaller f-stop (or a larger aperture). When it is decreased it is termed as a larger f-stop (or smaller aperture). Example of a small aperture is f/11. Example of a large aperture is f/2.8.


AF stands for auto-focus. This technology segregates from older manual focusing lenses that existed before auto-focusing lenses became a standard. There are some lenses which doesn’t have a built-in auto-focusing motor inside them. These are nevertheless sold as AF lenses. Such as the Nikkor 50mm f/1.8 D lens. These lenses autofocus on cameras that come with a built-in auto-focusing motor. Today all new lenses have built-in AF motor inside them.

Auto-focusing is a fantastic technology that automatically acquires focus by using either contrast or phase detection technology to detect the point of sharpest focus. Tiny adjustments are made in the focusing elements on the lens using motors inside till focus is locked.


With AF comes the other acronym MF. It stands for manual focusing. All lenses have the ability to focus manually. You just have to turn the focusing ring on the lens barrel to manually focus the lens. There are a large number of older lenses which focuses only manually. These are extremely sharp optical tools. The best thing is they are cheap if you can find them in the resale market.

Focusing technology

Focusing technology is basically the focusing motor that resides inside the lens. Older lenses have auto-focusing motors that are basically being phased out because of their noisy nature and slow performance. Canon, e.g., replaced the older micro-motor type USM’s with the new ring-type USM. Nikkor’s Silent Wave Motor (SWM) driven auto-focusing is yet another example. Canon recently launched the STM technology which stands for Stepping Motor. This is smoother and quieter and gives a more controlled auto-focusing experience when compared to older jerky type USM motors.

Image stabilization

lens stabilization

VR / IS / OS / O.I.S, no matter what it is called, image stabilization is a handy thing to have in your lens. It basically gives you the leverage to shoot at a shutter speed that is slower than the focal length you are shooting. This is something that is cardinal when it comes to shooting hand-held, especially when shooting in low light conditions.

Hope the above tips cleared some of your doubts. For more doubts mail us back and we can assist you with picking the right lens for the job. Also, watch out for the next article in this series – ‘A guide to choosing the right lens for the job’. Happy shooting.

Rajib Mukherjee

Rajib Mukherjee

Rajib’s love for the road is second only to his love for photography. Wanderlust at heart and a shutterbug who loves to document his travels via his lenses; his two passions compliment each other perfectly. He has been writing for over 6 years now, which unsurprisingly, revolve mostly around his two favourite pursuits.
Rajib Mukherjee